Cross-site Scripting (XSS) - Revision history

ErezYalon: Fixed typos

2018-06-05T08:30:52Z

Fixed typos

Jmanico: Undo revision 237086 by Hblankenship (talk) since it breaks the page on mobile and small screens - please add donation link to bottom

2018-03-06T20:52:20Z

Undo revision 237086 by Hblankenship (talk) since it breaks the page on mobile and small screens - please add donation link to bottom

Hblankenship: Added donate to OWASP button per OWASP Donation Initiative

2018-01-27T14:37:32Z

Added donate to OWASP button per OWASP Donation Initiative

Imifos: Removed the Java association since it's much broarder than Java

2016-06-04T13:18:46Z

Removed the Java association since it's much broarder than Java

Imifos: Category correction

2016-02-02T14:30:10Z

Category correction

Imifos at 13:06, 1 December 2015

2015-12-01T13:06:08Z

Jeff Knutson: Added anchor section for Stored and Reflected XSS Attacks to reference from .NET_AntiXSS_Library page

2014-04-23T04:07:49Z

Added anchor section for Stored and Reflected XSS Attacks to reference from .NET_AntiXSS_Library page

Jmanico: flagged as popular so it gets extra care.

2014-04-12T23:15:40Z

flagged as popular so it gets extra care.

Jmanico: abridged xss cheatsheet merged into main cheatsheet

2014-04-06T20:24:36Z

abridged xss cheatsheet merged into main cheatsheet

Andrew Smith: Addition of link to content spoofing

2014-04-01T18:57:14Z

Addition of link to content spoofing

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-{{template: Attack}}<br>
+{{template: Attack}}
 [[Category:OWASP ASDR Project]]
 Last revision (mm/dd/yy): '''{{REVISIONMONTH}}/{{REVISIONDAY}}/{{REVISIONYEAR}}'''
 [[Category:Security Focus Area]]
 __NOTOC__
 ==Overview==
-Cross-Site Scripting (XSS) attacks are a type of injection, in which malicious scripts are injected into otherwise benign and trusted web sites. XSS attacks occur when an attacker uses a web application to send malicious code, generally in the form of a browser side script, to a different end user. Flaws that allow these attacks to succeed are quite widespread and occur anywhere a web application uses input from a user within the output it generates without validating or encoding it.
+Cross-Site Scripting (XSS) attacks are a type of injection, in which malicious scripts are injected into otherwise benign and trusted websites. XSS attacks occur when an attacker uses a web application to send malicious code, generally in the form of a browser side script, to a different end user. Flaws that allow these attacks to succeed are quite widespread and occur anywhere a web application uses input from a user within the output it generates without validating or encoding it.
 An attacker can use XSS to send a malicious script to an unsuspecting user. The end user’s browser has no way to know that the script should not be trusted, and will execute the script. Because it thinks the script came from a trusted source, the malicious script can access any cookies, session tokens, or other sensitive information retained by the browser and used with that site. These scripts can even rewrite the content of the HTML page. For more details on the different types of XSS flaws, see: [[Types of Cross-Site Scripting]].
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 ===[[#Stored and Reflected XSS Attacks|Stored and Reflected XSS Attacks]]===
-XSS attacks can generally be categorized into two categories: stored and reflected. There is a third, much less well known type of XSS attack called [[DOM Based XSS |DOM Based XSS]] that is discussed seperately [[DOM Based XSS |here]].
+XSS attacks can generally be categorized into two categories: stored and reflected. There is a third, much less well-known type of XSS attack called [[DOM Based XSS |DOM Based XSS]] that is discussed separately [[DOM Based XSS |here]].
 ====Stored XSS Attacks====
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 ====Reflected XSS Attacks====
-Reflected attacks are those where the injected script is reflected off the web server, such as in an error message, search result, or any other response that includes some or all of the input sent to the server as part of the request. Reflected attacks are delivered to victims via another route, such as in an e-mail message, or on some other web site. When a user is tricked into clicking on a malicious link, submitting a specially crafted form, or even just browsing to a malicious site, the injected code travels to the vulnerable web site, which reflects the attack back to the user’s browser. The browser then executes the code because it came from a "trusted" server.  Reflected XSS is also sometimes referred to as Non-Persistent or Type-II XSS.
+Reflected attacks are those where the injected script is reflected off the web server, such as in an error message, search result, or any other response that includes some or all of the input sent to the server as part of the request. Reflected attacks are delivered to victims via another route, such as in an e-mail message, or on some other website. When a user is tricked into clicking on a malicious link, submitting a specially crafted form, or even just browsing to a malicious site, the injected code travels to the vulnerable web site, which reflects the attack back to the user’s browser. The browser then executes the code because it came from a "trusted" server.  Reflected XSS is also sometimes referred to as Non-Persistent or Type-II XSS.
 ===Other Types of XSS Vulnerabilities===
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 ====XSS Attack Consequences====
-The consequence of an XSS attack is the same regardless of whether it is stored or reflected ([[DOM Based XSS |or DOM Based]]). The difference is in how the payload arrives at the server. Do not be fooled into thinking that a “read only” or “brochureware” site is not vulnerable to serious reflected XSS attacks. XSS can cause a variety of problems for the end user that range in severity from an annoyance to complete account compromise. The most severe XSS attacks involve disclosure of the user’s session cookie, allowing an attacker to hijack the user’s session and take over the account. Other damaging attacks include the disclosure of end user files, installation of Trojan horse programs, redirect the user to some other page or site, or modify presentation of content. An XSS vulnerability allowing an attacker to modify a press release or news item could affect a company’s stock price or lessen consumer confidence. An XSS vulnerability on a pharmaceutical site could allow an attacker to modify dosage information resulting in an overdose. For more information on these types of attacks see [[Content_Spoofing]].
+The consequence of an XSS attack is the same regardless of whether it is stored or reflected ([[DOM Based XSS |or DOM Based]]). The difference is in how the payload arrives at the server. Do not be fooled into thinking that a “read-only” or “brochureware” site is not vulnerable to serious reflected XSS attacks. XSS can cause a variety of problems for the end user that range in severity from an annoyance to complete account compromise. The most severe XSS attacks involve disclosure of the user’s session cookie, allowing an attacker to hijack the user’s session and take over the account. Other damaging attacks include the disclosure of end user files, installation of Trojan horse programs, redirect the user to some other page or site, or modify presentation of content. An XSS vulnerability allowing an attacker to modify a press release or news item could affect a company’s stock price or lessen consumer confidence. An XSS vulnerability on a pharmaceutical site could allow an attacker to modify dosage information resulting in an overdose. For more information on these types of attacks see [[Content_Spoofing]].
 ===How to Determine If You Are Vulnerable===
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 The primary defenses against XSS are described in the [[XSS_(Cross_Site_Scripting)_Prevention_Cheat_Sheet |OWASP XSS Prevention Cheat Sheet]].
-Also, it's crucial that you turn off HTTP TRACE support on all webservers. An attacker can steal cookie data via Javascript even when document.cookie is disabled or not supported on the client. This attack is mounted when a user posts a malicious script to a forum so when another user clicks the link, an asynchronous HTTP Trace call is triggered which collects the user's cookie information from the server, and then sends it over to another malicious server that collects the cookie information so the attacker can mount a session hijack attack. This is easily mitigated by removing support for HTTP TRACE on all webservers.
+Also, it's crucial that you turn off HTTP TRACE support on all web servers. An attacker can steal cookie data via Javascript even when document.cookie is disabled or not supported by the client. This attack is mounted when a user posts a malicious script to a forum so when another user clicks the link, an asynchronous HTTP Trace call is triggered which collects the user's cookie information from the server, and then sends it over to another malicious server that collects the cookie information so the attacker can mount a session hijack attack. This is easily mitigated by removing support for HTTP TRACE on all web servers.
 The [[ESAPI |OWASP ESAPI project]] has produced a set of reusable security components in several languages, including validation and escaping routines to prevent parameter tampering and the injection of XSS attacks. In addition, the [[:Category:OWASP WebGoat Project|OWASP WebGoat Project]] training application has lessons on Cross-Site Scripting and data encoding.
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 <pre>
 <b onmouseover=alert('Wufff!')>click me!</b>
-</prE>
+</pre>
 onerror
 <pre>
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 == Examples ==
-Cross-site scripting attacks may occur anywhere that possibly malicious users are allowed to post unregulated material to a trusted web site for the consumption of other valid users.
+Cross-site scripting attacks may occur anywhere that possibly malicious users are allowed to post unregulated material to a trusted website for the consumption of other valid users.
-The most common example can be found in bulletin-board web sites which provide web based mailing list-style functionality.
+The most common example can be found in bulletin-board websites which provide web based mailing list-style functionality.
 ===Example 1===
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 The code in this example operates correctly if eid contains only standard alphanumeric text. If eid has a value that includes meta-characters or source code, then the code will be executed by the web browser as it displays the HTTP response.
-Initially this might not appear to be much of a vulnerability. After all, why would someone enter a URL that causes malicious code to run on their own computer? The real danger is that an attacker will create the malicious URL, then use e-mail or social engineering tricks to lure victims into visiting a link to the URL. When victims click the link, they unwittingly reflect the malicious content through the vulnerable web application back to their own computers. This mechanism of exploiting vulnerable web applications is known as Reflected XSS.
+Initially, this might not appear to be much of a vulnerability. After all, why would someone enter a URL that causes malicious code to run on their own computer? The real danger is that an attacker will create the malicious URL, then use e-mail or social engineering tricks to lure victims into visiting a link to the URL. When victims click the link, they unwittingly reflect the malicious content through the vulnerable web application back to their own computers. This mechanism of exploiting vulnerable web applications is known as Reflected XSS.
 ===Example 2===
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 </pre>
-As in Example 1, this code functions correctly when the values of name are well-behaved, but it does nothing to prevent exploits if they are not. Again, this code can appear less dangerous because the value of name is read from a database, whose contents are apparently managed by the application. However, if the value of name originates from user-supplied data, then the database can be a conduit for malicious content. Without proper input validation on all data stored in the database, an attacker can execute malicious commands in the user's web browser. This type of exploit, known as Stored XSS, is particularly insidious because the indirection caused by the data store makes it more difficult to identify the threat and increases the possibility that the attack will affect multiple users. XSS got its start in this form with web sites that offered a "guestbook" to visitors. Attackers would include JavaScript in their guestbook entries, and all subsequent visitors to the guestbook page would execute the malicious code.
+As in Example 1, this code functions correctly when the values of name are well-behaved, but it does nothing to prevent exploits if they are not. Again, this code can appear less dangerous because the value of name is read from a database, whose contents are apparently managed by the application. However, if the value of name originates from user-supplied data, then the database can be a conduit for malicious content. Without proper input validation on all data stored in the database, an attacker can execute malicious commands in the user's web browser. This type of exploit, known as Stored XSS, is particularly insidious because the indirection caused by the data store makes it more difficult to identify the threat and increases the possibility that the attack will affect multiple users. XSS got its start in this form with websites that offered a "guestbook" to visitors. Attackers would include JavaScript in their guestbook entries, and all subsequent visitors to the guestbook page would execute the malicious code.
 As the examples demonstrate, XSS vulnerabilities are caused by code that includes unvalidated data in an HTTP response. There are three vectors by which an XSS attack can reach a victim:
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 === Attack Examples ===
-'''Example 1 : Cookie Grabber'''
+'''Example 1: Cookie Grabber'''
 If the application doesn't validate the input data, the attacker can easily steal a cookie from an authenticated user. All the attacker has to do is to place the following code in any posted input(ie: message boards, private messages, user profiles):

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 Last revision (mm/dd/yy): '''{{REVISIONMONTH}}/{{REVISIONDAY}}/{{REVISIONYEAR}}'''
 [[Category:Security Focus Area]]
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 * XSSed - Cross-Site Scripting (XSS) Information and Mirror Archive of Vulnerable Websites http://www.xssed.com
 <br>
 [[Category:Injection]]

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 Last revision (mm/dd/yy): '''{{REVISIONMONTH}}/{{REVISIONDAY}}/{{REVISIONYEAR}}'''
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 * XSSed - Cross-Site Scripting (XSS) Information and Mirror Archive of Vulnerable Websites http://www.xssed.com
 <br>
 [[Category:Injection]]

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 [[Category:Injection]]
 [[Category:OWASP Top Ten Project]]
 [[Category:Code Snippet]]
 [[Category:Security Focus Area]]
 [[Category:Attack]]
 [[Category:Popular]]

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 [[Category:Injection]]
 [[Category:OWASP Top Ten Project]]
-[[Category:OWASP Java Project]]
+[[Category:Java]]
 [[Category:Code Snippet]]
 [[Category:Security Focus Area]]
 [[Category:Attack]]
 [[Category:Popular]]

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 The malicious content sent to the web browser often takes the form of a segment of JavaScript, but may also include HTML, Flash, or any other type of code that the browser may execute. The variety of attacks based on XSS is almost limitless, but they commonly include transmitting private data, like cookies or other session information, to the attacker, redirecting the victim to web content controlled by the attacker, or performing other malicious operations on the user's machine under the guise of the vulnerable site.
-===Stored and Reflected XSS Attacks===
+===[[#Stored and Reflected XSS Attacks|Stored and Reflected XSS Attacks]]===
 XSS attacks can generally be categorized into two categories: stored and reflected. There is a third, much less well known type of XSS attack called [[DOM Based XSS |DOM Based XSS]] that is discussed seperately [[DOM Based XSS |here]].

← Older revision		Revision as of 23:15, 12 April 2014
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	[[Category:Attack]]		[[Category:Attack]]
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← Older revision		Revision as of 20:24, 6 April 2014
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	See the [[XSS (Cross Site Scripting) Prevention Cheat Sheet]]		See the [[XSS (Cross Site Scripting) Prevention Cheat Sheet]]
−
−	~~See the [[Abridged XSS Prevention Cheat Sheet]]~~

	See the [[DOM based XSS Prevention Cheat Sheet]]		See the [[DOM based XSS Prevention Cheat Sheet]]