https://wiki.owasp.org/index.php?title=How_CSRFGuard_Works&feed=atom&action=historyHow CSRFGuard Works - Revision history2024-03-29T06:04:51ZRevision history for this page on the wikiMediaWiki 1.27.2https://wiki.owasp.org/index.php?title=How_CSRFGuard_Works&diff=177380&oldid=prevAzzeddine RAMRAMI at 18:54, 22 June 20142014-06-22T18:54:58Z<p></p>
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<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 18:54, 22 June 2014</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>== Overview ==</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>== Overview ==</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The core issue with CSRF attacks is that form submission can be imitated with forged requests. The application must be able to differentiate between legal requests and forged requests. Since all headers, cookies, and credentials will be submitted with both legal and forged requests, the only method of truly verifying the integrity of the request is with a uniquely identifiable token in the form of an HTTP parameter<del class="diffchange diffchange-inline">. When the user first visits the site, the application will generate and store a ''session specific'' unique request token. This session specific unique request token is then placed in each form and link of the HTML response, ensuring that this value will be submitted with the next request. For each subsequent request, the application must verify the existence of the unique token parameter and compare its value to that of the value stored in the user's session. The security of the approach is based on the fact that this unique token value is specific to a user's session and is ''hard to guess.'' Therefore, it is imperative that this value is large and cryptographically secure</del>.</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The core issue with CSRF attacks is that form submission can be imitated with forged requests. The application must be able to differentiate between legal requests and forged requests. Since all headers, cookies, and credentials will be submitted with both legal and forged requests, the only method of truly verifying the integrity of the request is with a uniquely identifiable token in the form of an HTTP parameter.  </div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">== Java EE Filters ==</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">OWASP CSRFGuard implements a variant of the synchronizer token pattern to mitigate the risk of CSRF attacks. In order to implement this pattern, CSRFGuard must offer the capability to place the CSRF prevention token within the HTML produced by the protected web application. CSRFGuard 3 provides developers more fine grain control over the injection of the token. Developers can inject the token in their HTML using either dynamic JavaScript DOM manipulation or a JSP tag library. CSRFGuard no longer intercepts and modifies the HttpServletResponse object as was done in previous releases. The currently available token injection strategies are designed to make the integration of CSRFGuard more feasible and scalable within current enterprise web applications. Developers are encouraged to make use of both the JavaScript DOM Manipulation and the JSP tag library strategies for a complete token injection strategy. The JavaScript DOM Manipulation strategy is ideal as it is automated and requires minimal effort on behalf of the developer. In the event the JavaScript solution is insufficient within a particular application context, developers should leverage the JSP tag library. The purpose of this article is to describe the token injection strategies offered by OWASP CSRFGuard 3.</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Java EE <del class="diffchange diffchange-inline">filters provide the ability to intercept, view, and modify both the request and associated response for the requesting client. </del>Filters <del class="diffchange diffchange-inline">are inserted </del>and <del class="diffchange diffchange-inline">executed by the Java EE container's deployment descriptor (web.xml) file. For example, if an HTTP request for a JSP page hits our Apache web server, the request is sent to Tomcat for processing. Before Tomcat executes the code inside of the JSP, the request must be passed along a chain of Java EE filters. The following snippet was taken from the [http://www.owasp.org/index.php/CSRFGuard_1.x_Installation OWASP CSRFGuard 1.x installation instructions] as it illustrates how to declare and map a filter to a particular URI-space in web.xml:</del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">== </ins>Java EE Filters <ins class="diffchange diffchange-inline">- Declare </ins>and <ins class="diffchange diffchange-inline">Configure JavaScriptServlet ==</ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>  <<del class="diffchange diffchange-inline">filter</del>></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">The JavaScript file used for token injection is dynamically generated by the JavaScriptServlet class using a template file. Ensure that the Owasp.CsrfGuard.jar file is found within the target application's classpath. Copy the Owasp.CsrfGuard.js template file from the OWASP CSRFGuard distribution folder to a non-publicly accessible directory within the target application. For the remainder of this section, we assume the Owasp.CsrfGuard.js template file was placed in the application's WEB-INF folder. Edit the deployment descriptor (web.xml) to declare the JavaScriptServlet class along with any associated initialization parameters. Consider the following configuration snippet taken from the [https://github.com/esheri3/OWASP-CSRFGuard/tree/master/Owasp.CsrfGuard.Test Owasp.CsrfGuard.Test] application:</ins></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">    </del><<del class="diffchange diffchange-inline">filter</del>-name><del class="diffchange diffchange-inline">CSRFGuard</del></<del class="diffchange diffchange-inline">filter</del>-name></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div> </div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">    </del><<del class="diffchange diffchange-inline">filter</del>-class>org.owasp.<del class="diffchange diffchange-inline">csrf</del>.<del class="diffchange diffchange-inline">CSRFGuard</del></<del class="diffchange diffchange-inline">filter</del>-class></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>  <<ins class="diffchange diffchange-inline">servlet</ins>></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">      </ins><<ins class="diffchange diffchange-inline">servlet</ins>-name><ins class="diffchange diffchange-inline">JavaScriptServlet</ins></<ins class="diffchange diffchange-inline">servlet</ins>-name></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">      </ins><<ins class="diffchange diffchange-inline">servlet</ins>-class>org.owasp.<ins class="diffchange diffchange-inline">csrfguard.servlet</ins>.<ins class="diffchange diffchange-inline">JavaScriptServlet</ins></<ins class="diffchange diffchange-inline">servlet</ins>-class<ins class="diffchange diffchange-inline">></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">      <init-param></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">          <param-name>source-file</param-name></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">          <param-value>WEB-INF/Owasp.CsrfGuard.js</param-value></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">      </init-param</ins>></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>       <init-param></div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>       <init-param></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">        </del><param-name><del class="diffchange diffchange-inline">error</del>-<del class="diffchange diffchange-inline">page</del></param-name></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">          </ins><param-name><ins class="diffchange diffchange-inline">inject</ins>-<ins class="diffchange diffchange-inline">into-forms</ins></param-name></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">        </del><param-value><del class="diffchange diffchange-inline">error.jsp</del></param-value></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">          </ins><param-value><ins class="diffchange diffchange-inline">true</ins></param-value></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>       </init-param></div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>       </init-param></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline"> </del></<del class="diffchange diffchange-inline">filter</del>></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">      <init-param></ins></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline"> </del></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">          <param-name>inject-into-attributes</param-name></ins></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline"> </del><<del class="diffchange diffchange-inline">filter</del>-<del class="diffchange diffchange-inline">mapping</del>></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">          <param-value>true</ins></<ins class="diffchange diffchange-inline">param-value</ins>></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">  </del><<del class="diffchange diffchange-inline">filter</del>-name><del class="diffchange diffchange-inline">CSRFGuard</del></<del class="diffchange diffchange-inline">filter</del>-name></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">      </init-param></ins></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">  </del><<del class="diffchange diffchange-inline">url</del>-<del class="diffchange diffchange-inline">pattern</del>>/<del class="diffchange diffchange-inline">*</del></<del class="diffchange diffchange-inline">url</del>-pattern></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">    </ins><<ins class="diffchange diffchange-inline">init</ins>-<ins class="diffchange diffchange-inline">param</ins>></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline"> </del></<del class="diffchange diffchange-inline">filter</del>-<del class="diffchange diffchange-inline">mapping</del>></div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">          </ins><<ins class="diffchange diffchange-inline">param</ins>-name><ins class="diffchange diffchange-inline">domain-strict</ins></<ins class="diffchange diffchange-inline">param</ins>-name></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div> </div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">          </ins><<ins class="diffchange diffchange-inline">param</ins>-<ins class="diffchange diffchange-inline">value</ins>><ins class="diffchange diffchange-inline">false<</ins>/<ins class="diffchange diffchange-inline">param-value></ins></div></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div> </div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">    </ins></<ins class="diffchange diffchange-inline">init-param></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">    <init-param></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">          <param-name>referer</ins>-pattern<ins class="diffchange diffchange-inline"></param-name</ins>></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">          <param-value>.*localhost.*</ins></<ins class="diffchange diffchange-inline">param</ins>-<ins class="diffchange diffchange-inline">value</ins>></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline">    </init-param></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins class="diffchange diffchange-inline"> </servlet></ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Implementing the CSRF Guard as a Java EE Filter gives us the ability to verify the integrity of the request before it ever hits our web application.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Implementing the CSRF Guard as a Java EE Filter gives us the ability to verify the integrity of the request before it ever hits our web application.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
</table>Azzeddine RAMRAMIhttps://wiki.owasp.org/index.php?title=How_CSRFGuard_Works&diff=89538&oldid=prevJmanico at 00:59, 19 September 20102010-09-19T00:59:05Z<p></p>
<table class="diff diff-contentalign-left" data-mw="interface">
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<tr style='vertical-align: top;' lang='en'>
<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 00:59, 19 September 2010</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l1" >Line 1:</td>
<td colspan="2" class="diff-lineno">Line 1:</td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">==Warning==</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;">CSRFGuard is a "reference implementation". Developers are encouraged to leverage more tightly integrated solutions for performance (ex: speed of parsing HTML) and technical (ex: AJAX requests) challenges.</ins></div></td></tr>
<tr><td colspan="2"> </td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div><ins style="font-weight: bold; text-decoration: none;"></ins></div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>== Overview ==</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>== Overview ==</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
</table>Jmanicohttps://wiki.owasp.org/index.php?title=How_CSRFGuard_Works&diff=22510&oldid=prevEsheridan at 21:07, 20 October 20072007-10-20T21:07:55Z<p></p>
<table class="diff diff-contentalign-left" data-mw="interface">
<col class='diff-marker' />
<col class='diff-content' />
<col class='diff-marker' />
<col class='diff-content' />
<tr style='vertical-align: top;' lang='en'>
<td colspan='2' style="background-color: white; color:black; text-align: center;">← Older revision</td>
<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 21:07, 20 October 2007</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l1" >Line 1:</td>
<td colspan="2" class="diff-lineno">Line 1:</td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>== <del class="diffchange diffchange-inline">How Does OWASP CSRFGuard Work? </del>==</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>== <ins class="diffchange diffchange-inline">Overview </ins>==</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The core issue with CSRF attacks is that form submission can be imitated with forged requests. The application must be able to differentiate between legal requests and forged requests. Since all headers, cookies, and credentials will be submitted with both legal and forged requests, the only method of truly verifying the integrity of the request is with a uniquely identifiable token in the form of an HTTP parameter. When the user first visits the site, the application will generate and store a ''session specific'' unique request token. This session specific unique request token is then placed in each form and link of the HTML response, ensuring that this value will be submitted with the next request. For each subsequent request, the application must verify the existence of the unique token parameter and compare its value to that of the value stored in the user's session. The security of the approach is based on the fact that this unique token value is specific to a user's session and is ''hard to guess.'' Therefore, it is imperative that this value is large and cryptographically secure.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The core issue with CSRF attacks is that form submission can be imitated with forged requests. The application must be able to differentiate between legal requests and forged requests. Since all headers, cookies, and credentials will be submitted with both legal and forged requests, the only method of truly verifying the integrity of the request is with a uniquely identifiable token in the form of an HTTP parameter. When the user first visits the site, the application will generate and store a ''session specific'' unique request token. This session specific unique request token is then placed in each form and link of the HTML response, ensuring that this value will be submitted with the next request. For each subsequent request, the application must verify the existence of the unique token parameter and compare its value to that of the value stored in the user's session. The security of the approach is based on the fact that this unique token value is specific to a user's session and is ''hard to guess.'' Therefore, it is imperative that this value is large and cryptographically secure.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">=</del>== Java EE Filters <del class="diffchange diffchange-inline">=</del>==</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>== Java EE Filters ==</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Java EE filters provide the ability to intercept, view, and modify both the request and associated response for the requesting client. Filters are inserted and executed by the Java EE container's deployment descriptor (web.xml) file. For example, if an HTTP request for a JSP page hits our Apache web server, the request is sent to Tomcat for processing. Before Tomcat executes the code inside of the JSP, the request must be passed along a chain of Java EE filters. The following snippet was taken from the [http://www.owasp.org/index.php/CSRFGuard_1.x_Installation OWASP CSRFGuard 1.x installation instructions] as it illustrates how to declare and map a filter to a particular URI-space in web.xml:</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Java EE filters provide the ability to intercept, view, and modify both the request and associated response for the requesting client. Filters are inserted and executed by the Java EE container's deployment descriptor (web.xml) file. For example, if an HTTP request for a JSP page hits our Apache web server, the request is sent to Tomcat for processing. Before Tomcat executes the code inside of the JSP, the request must be passed along a chain of Java EE filters. The following snippet was taken from the [http://www.owasp.org/index.php/CSRFGuard_1.x_Installation OWASP CSRFGuard 1.x installation instructions] as it illustrates how to declare and map a filter to a particular URI-space in web.xml:</div></td></tr>
<tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l24" >Line 24:</td>
<td colspan="2" class="diff-lineno">Line 24:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Implementing the CSRF Guard as a Java EE Filter gives us the ability to verify the integrity of the request before it ever hits our web application.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>Implementing the CSRF Guard as a Java EE Filter gives us the ability to verify the integrity of the request before it ever hits our web application.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">=</del>== Generating the Unique Request Token: Secure Random <del class="diffchange diffchange-inline">=</del>==</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>== Generating the Unique Request Token: Secure Random ==</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>When implementing the CSRF Guard, we must ensure that the unique request token is cryptographically strong. After all, our implementation relies on the principle that the unique token is difficult to guess. If the unique request token can be easily guessed then a CSRF attack can be executed.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>When implementing the CSRF Guard, we must ensure that the unique request token is cryptographically strong. After all, our implementation relies on the principle that the unique token is difficult to guess. If the unique request token can be easily guessed then a CSRF attack can be executed.</div></td></tr>
<tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l40" >Line 40:</td>
<td colspan="2" class="diff-lineno">Line 40:</td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     }</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>     }</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">=</del>== Implementation <del class="diffchange diffchange-inline">=</del>==</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>== Implementation ==</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The OWASP CSRF Java EE Filter will attempt to verify the integrity of the request by comparing the unique request token HTTP parameter value with that of the token stored in the session. If the two values do not match, then we assume the request is forged and we invalidate the existing session and redirect the user to an error page. If the parameter value equals the corresponding session attribute value, then we call doChain() and pass the request to the web application. Once the web application is finished processing the request, the filter will search the HTML response for forms and links and insert the appropriate unique token parameter value. Unfortunately, the dependency on an HTML response means that the current filter may not work with some Web 2.0 applications.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>The OWASP CSRF Java EE Filter will attempt to verify the integrity of the request by comparing the unique request token HTTP parameter value with that of the token stored in the session. If the two values do not match, then we assume the request is forged and we invalidate the existing session and redirect the user to an error page. If the parameter value equals the corresponding session attribute value, then we call doChain() and pass the request to the web application. Once the web application is finished processing the request, the filter will search the HTML response for forms and links and insert the appropriate unique token parameter value. Unfortunately, the dependency on an HTML response means that the current filter may not work with some Web 2.0 applications.</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div><del class="diffchange diffchange-inline">=</del>== Bypass CSRFGuard With Stored XSS <del class="diffchange diffchange-inline">=</del>==</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>== Bypass CSRFGuard With Stored XSS ==</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>There have been discussions suggesting that the unique request token can be compromised using JavaScript. This attack implies that the application also contains a stored cross-site scripting vulnerability, which is frequently a more severe issue than cross-site request forgery. The first MySpace worm worked in this manner where it used a Cross Site Scripting vulnerability to forge requests to update a user's profile, where the user profile update mechanism was protected with a CSRF defense mechanism similar to what is provided by this filter. If your application contains a stored cross-site scripting vulnerability, then the unique request token can be parsed from the HTML response to successfully forge form submissions.</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>There have been discussions suggesting that the unique request token can be compromised using JavaScript. This attack implies that the application also contains a stored cross-site scripting vulnerability, which is frequently a more severe issue than cross-site request forgery. The first MySpace worm worked in this manner where it used a Cross Site Scripting vulnerability to forge requests to update a user's profile, where the user profile update mechanism was protected with a CSRF defense mechanism similar to what is provided by this filter. If your application contains a stored cross-site scripting vulnerability, then the unique request token can be parsed from the HTML response to successfully forge form submissions.</div></td></tr>
</table>Esheridanhttps://wiki.owasp.org/index.php?title=How_CSRFGuard_Works&diff=22507&oldid=prevEsheridan at 15:31, 20 October 20072007-10-20T15:31:08Z<p></p>
<table class="diff diff-contentalign-left" data-mw="interface">
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<td colspan='2' style="background-color: white; color:black; text-align: center;">Revision as of 15:31, 20 October 2007</td>
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<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Java EE Filters ===</div></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"><div>=== Java EE Filters ===</div></td></tr>
<tr><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td><td class='diff-marker'> </td><td style="background-color: #f9f9f9; color: #333333; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #e6e6e6; vertical-align: top; white-space: pre-wrap;"></td></tr>
<tr><td class='diff-marker'>−</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Java EE filters provide the ability to intercept, view, and modify both the request and associated response for the requesting client. Filters are inserted and executed by the Java EE container's deployment descriptor (web.xml) file. For example, if an HTTP request for a JSP page hits our Apache web server, the request is sent to Tomcat for processing. Before Tomcat executes the code inside of the JSP, the request must be passed along a chain of Java EE filters. The following snippet illustrates how to declare and map a filter to a particular URI-space in web.xml:</div></td><td class='diff-marker'>+</td><td style="color:black; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Java EE filters provide the ability to intercept, view, and modify both the request and associated response for the requesting client. Filters are inserted and executed by the Java EE container's deployment descriptor (web.xml) file. For example, if an HTTP request for a JSP page hits our Apache web server, the request is sent to Tomcat for processing. Before Tomcat executes the code inside of the JSP, the request must be passed along a chain of Java EE filters. The following snippet <ins class="diffchange diffchange-inline">was taken from the [http://www.owasp.org/index.php/CSRFGuard_1.x_Installation OWASP CSRFGuard 1.x installation instructions] as it </ins>illustrates how to declare and map a filter to a particular URI-space in web.xml:</div></td></tr>
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</table>Esheridanhttps://wiki.owasp.org/index.php?title=How_CSRFGuard_Works&diff=22504&oldid=prevEsheridan: New page: == How Does OWASP CSRFGuard Work? == The core issue with CSRF attacks is that form submission can be imitated with forged requests. The application must be able to differentiate between l...2007-10-20T15:28:22Z<p>New page: == How Does OWASP CSRFGuard Work? == The core issue with CSRF attacks is that form submission can be imitated with forged requests. The application must be able to differentiate between l...</p>
<p><b>New page</b></p><div>== How Does OWASP CSRFGuard Work? ==<br />
<br />
The core issue with CSRF attacks is that form submission can be imitated with forged requests. The application must be able to differentiate between legal requests and forged requests. Since all headers, cookies, and credentials will be submitted with both legal and forged requests, the only method of truly verifying the integrity of the request is with a uniquely identifiable token in the form of an HTTP parameter. When the user first visits the site, the application will generate and store a ''session specific'' unique request token. This session specific unique request token is then placed in each form and link of the HTML response, ensuring that this value will be submitted with the next request. For each subsequent request, the application must verify the existence of the unique token parameter and compare its value to that of the value stored in the user's session. The security of the approach is based on the fact that this unique token value is specific to a user's session and is ''hard to guess.'' Therefore, it is imperative that this value is large and cryptographically secure.<br />
<br />
=== Java EE Filters ===<br />
<br />
Java EE filters provide the ability to intercept, view, and modify both the request and associated response for the requesting client. Filters are inserted and executed by the Java EE container's deployment descriptor (web.xml) file. For example, if an HTTP request for a JSP page hits our Apache web server, the request is sent to Tomcat for processing. Before Tomcat executes the code inside of the JSP, the request must be passed along a chain of Java EE filters. The following snippet illustrates how to declare and map a filter to a particular URI-space in web.xml:<br />
<br />
<filter><br />
<filter-name>CSRFGuard</filter-name><br />
<filter-class>org.owasp.csrf.CSRFGuard</filter-class><br />
<init-param><br />
<param-name>error-page</param-name><br />
<param-value>error.jsp</param-value><br />
</init-param><br />
</filter><br />
<br />
<filter-mapping><br />
<filter-name>CSRFGuard</filter-name><br />
<url-pattern>/*</url-pattern><br />
</filter-mapping><br />
<br />
<br />
Implementing the CSRF Guard as a Java EE Filter gives us the ability to verify the integrity of the request before it ever hits our web application.<br />
<br />
=== Generating the Unique Request Token: Secure Random ===<br />
<br />
When implementing the CSRF Guard, we must ensure that the unique request token is cryptographically strong. After all, our implementation relies on the principle that the unique token is difficult to guess. If the unique request token can be easily guessed then a CSRF attack can be executed.<br />
<br />
The following code snippet generates a BASE64 encoded string of 'size' bytes:<br />
<br />
private String generateCSRFToken(int size) throws NoSuchAlgorithmException {<br />
SecureRandom sr = null;<br />
byte[] random = new byte[size];<br />
BASE64Encoder encoder = new BASE64Encoder();<br />
<br />
sr = SecureRandom.getInstance("SHA1PRNG");<br />
sr.nextBytes(random);<br />
return encoder.encode(random);<br />
}<br />
<br />
=== Implementation ===<br />
<br />
The OWASP CSRF Java EE Filter will attempt to verify the integrity of the request by comparing the unique request token HTTP parameter value with that of the token stored in the session. If the two values do not match, then we assume the request is forged and we invalidate the existing session and redirect the user to an error page. If the parameter value equals the corresponding session attribute value, then we call doChain() and pass the request to the web application. Once the web application is finished processing the request, the filter will search the HTML response for forms and links and insert the appropriate unique token parameter value. Unfortunately, the dependency on an HTML response means that the current filter may not work with some Web 2.0 applications.<br />
<br />
=== Bypass CSRFGuard With Stored XSS ===<br />
<br />
There have been discussions suggesting that the unique request token can be compromised using JavaScript. This attack implies that the application also contains a stored cross-site scripting vulnerability, which is frequently a more severe issue than cross-site request forgery. The first MySpace worm worked in this manner where it used a Cross Site Scripting vulnerability to forge requests to update a user's profile, where the user profile update mechanism was protected with a CSRF defense mechanism similar to what is provided by this filter. If your application contains a stored cross-site scripting vulnerability, then the unique request token can be parsed from the HTML response to successfully forge form submissions.</div>Esheridan