Difference between pages "Top 10 2010-A1-Injection" and "Top 10 2010-A2-Cross-Site Scripting (XSS)"

Revision as of 15:54, 22 April 2010

NOTE: THIS IS NOT THE LATEST VERSION. Please visit the OWASP Top 10 project page to find the latest edition.

A3-Broken Authentication and Session Management →

Threat Agents	Attack Vectors	Security Weakness		Technical Impacts	Business Impacts
______	Exploitability AVERAGE	Prevalence VERY WIDESPREAD	Detectability EASY	Impact MODERATE	______
Consider anyone who can send untrusted data to the system, including external users, internal users, and administrators.	Attacker sends text- based attack scripts that exploit the interpreter in the browser. Almost any source of data can be an attack vector, including internal sources such as data from the database.	XSS is the most prevalent web application security flaw. XSS flaws occur when an application includes user supplied data in a page sent to the browser without properly validating or escaping that content. There are three known types of XSS flaws: 1) Stored, 2) Reflected, and 3) DOM based XSS. Detection of most XSS flaws is fairly easy via testing or code analysis.		Attackers can execute scripts in a victim’s browser to hijack user sessions, deface web sites, insert hostile content, redirect users, hijack the user’s browser using malware, etc.	Consider the business value of the affected system and all the data it processes. Also consider the business impact of public exposure of the vulnerability.

Am I Vulnerable to XSS?

You need to ensure that all user supplied input sent back to the browser is verified to be safe (via input validation), and that user input is properly escaped before it is included in the output page. Proper output encoding ensures that such input is always treated as text in the browser, rather than active content that might get executed.

Both static and dynamic tools can find some XSS problems automatically. However, each application builds output pages differently and uses different browser side interpreters such as JavaScript, ActiveX, Flash, and Silverlight, which makes automated detection difficult. Therefore, complete coverage requires a combination of manual code review and manual penetration testing, in addition to any automated approaches in use.

Web 2.0 technologies, such as AJAX, make XSS much more difficult to detect via automated tools.

How Do I Prevent XSS?

Preventing XSS requires keeping untrusted data separate from active browser content.

The preferred option is to properly escape all untrusted data based on the HTML context (body, attribute, JavaScript, CSS, or URL) that the data will be placed into. Developers need to include this escaping in their applications unless their UI framework does this for them. See the OWASP XSS Prevention Cheat Sheet for more information about data escaping techniques.
Positive or “whitelist” input validation with appropriate canonicalization and decoding is also recommended as it helps protect against XSS, but is not a complete defense as many applications require special characters in their input. Such validation should, as much as possible, decode any encoded input, and then validate the length, characters, format, and any business rules on that data before accepting the input.

Example Attack Scenarios

The application uses untrusted data in the construction of the following HTML snippet without validation or escaping:

The attacker modifies the ‘CC’ parameter in their browser to:

This causes the victim’s session ID to be sent to the attacker’s website, allowing the attacker to hijack the user’s current session.

Note that attackers can also use XSS to defeat any automated CSRF defense the application might employ. See A5 for info on CSRF.

References

OWASP

External

← A1-Injection

Top 10 Introduction
Top 10 Risks

A3-Broken Authentication and Session Management →

@@ Line 1: / Line 1: @@
-{{Top_10_2010:TopTemplate|usenext=2010NextLink|next=A2-Cross-Site Scripting (XSS)|useprev=2010PrevLink|prev=Main}}
+{{Top_10_2010:TopTemplate|useprev=2010PrevLink|usenext=2010NextLink|prev=A1-Injection|next=A3-Broken Authentication and Session Management}}
 <center>
 {| style="align:center; text-align:center; border:2px solid #4F81BD; background-color:#F2F2F2; padding=2;"
@@ Line 9: / Line 10: @@
 |-
 | style="background-color: #D9D9D9; color: #000000;" | ______
-| style="background-color: #FF0000; color: #000000;" | '''Exploitability<br>EASY'''
+| style="background-color: #FFB200; color: #000000;" | '''Exploitability<br>AVERAGE
-| style="background-color: #FFB200; color: #000000;" | '''Prevalence<br>COMMON'''
+| style="background-color: #FF00FF; color: #000000;" | '''Prevalence<br>VERY WIDESPREAD
-| style="background-color: #FFB200; color: #000000;" | '''Detectability<br>AVERAGE'''
+| style="background-color: #FF0000; color: #000000;" | '''Detectability<br>EASY
-| style="background-color: #FF0000; color: #000000;" | '''Impact<br>SIMPLE'''
+| style="background-color: #FFB200; color: #000000;" | '''Impact<br>MODERATE
 | style="background-color: #D9D9D9; color: #000000;" | ______
 |-
-| style="text-align: left; border: 2px solid #FFFFFF;" |Consider anyone who can send untrusted data to the system, including external users, internal users, and administrators.
+| style="text-align: left; border: 2px solid #FFFFFF;" | Consider anyone who can send untrusted data to the system, including external users, internal users, and administrators.
-| style="text-align: left; border: 2px solid #FFFFFF;" | Attacker sends simple text-based attacks that exploit the syntax of the targeted interpreter. Almost any source of data can be an injection vector, including internal sources.
+| style="text-align: left; border: 2px solid #FFFFFF;" | Attacker sends text- based attack scripts that exploit the interpreter in the browser. Almost any source of data can be an attack vector, including internal sources such as data from the database.
-| colspan="2" style="text-align: left;border: 2px solid #FFFFFF;" | Injection flaws occur when an application sends untrusted data to an interpreter. Injection flaws are very prevalent, particularly in legacy code, often found in SQL queries, LDAP queries, XPath queries, OS commands, program arguments, etc. Injection flaws are easy to discover when examining code, but more difficult via testing. Scanners and fuzzers can help attackers find them.
+| colspan="2" style="text-align: left;border: 2px solid #FFFFFF;" | [[Cross-site_Scripting_(XSS) | XSS]] is the most prevalent web application security flaw. XSS flaws occur when an application includes user supplied data in a page sent to the browser without properly validating or escaping that content. There are three known types of XSS flaws: 1) [[Cross-site_Scripting_(XSS)#Stored_XSS_Attacks | Stored]], 2) [[Cross-site_Scripting_(XSS)#Reflected_XSS_Attacks | Reflected]], and 3) [[DOM_Based_XSS | DOM based XSS]].
-| style="text-align: left; border: 2px solid #FFFFFF;" | Injection can result in data loss or corruption, lack of accountability, or denial of access. Injection can sometimes lead to complete host takeover.
-| style="text-align: left; border: 2px solid #FFFFFF;" | Consider the business value of the affected data and the platform running the interpreter. All data could be stolen, modified, or deleted. Could your reputation be harmed?
+Detection of most XSS flaws is fairly easy via testing or code analysis.
+| style="text-align: left; border: 2px solid #FFFFFF;" | Attackers can execute scripts in a victim’s browser to hijack user sessions, deface web sites, insert hostile content, redirect users, hijack the user’s browser using malware, etc.
+| style="text-align: left; border: 2px solid #FFFFFF;" | Consider the business value of the affected system and all the data it processes.
+Also consider the business impact of public exposure of the vulnerability.
 |}
 </center>
+{{Top_10_2010:SubsectionVulnerableTemplate|XSS|
+You need to ensure that all user supplied input sent back to the browser is verified to be safe (via input validation), and that user input is properly escaped before it is included in the output page. Proper output encoding ensures that such input is always treated as text in the browser, rather than active content that might get executed.
-{{Top_10_2010:SubsectionVulnerableTemplate|Injection|
+Both static and dynamic tools can find some XSS problems automatically. However, each application builds output pages differently and uses different browser side interpreters such as JavaScript, ActiveX, Flash, and Silverlight, which makes automated detection difficult. Therefore, complete coverage requires a combination of manual code review and manual penetration testing, in addition to any automated approaches in use.
-The best way to find out if an application is vulnerable to injection is to verify that all use of interpreters clearly separates untrusted data from the command or query. For SQL calls, this means using bind variables in all prepared statements and stored procedures, and avoiding dynamic queries.
-Checking the code is a fast and accurate way to see if the application uses interpreters safely. Code analysis tools can help a security analyst find the use of interpreters and trace the data flow through the application. Manual penetration testers can confirm these issues by crafting exploits that confirm the vulnerability.
+Web 2.0 technologies, such as AJAX, make XSS much more difficult to detect via automated tools.
+}}
-Automated dynamic scanning which exercises the application may provide insight into whether some exploitable injection problems exist. Scanners cannot always reach interpreters and can have difficulty detecting whether an attack was successful.
+{{Top_10_2010:SubsectionPreventionTemplate|XSS|
+Preventing XSS requires keeping untrusted data separate from active browser content.
+# The preferred option is to properly escape all untrusted data based on the HTML context (body, attribute, JavaScript, CSS, or URL) that the data will be placed into. Developers need to include this escaping in their applications unless their UI framework does this for them. See the [[XSS_(Cross_Site_Scripting)_Prevention_Cheat_Sheet | OWASP XSS Prevention Cheat Sheet]] for more information about data escaping techniques.
+# Positive or “whitelist” input validation with appropriate canonicalization and decoding is also recommended as it helps protect against XSS, but is <u>not a complete defense</u> as many applications require special characters in their input. Such validation should, as much as possible, decode any encoded input, and then validate the length, characters, format, and any business rules on that data before accepting the input.
 }}
-{{Top_10_2010:SubsectionPreventionTemplate|Injection|
+{{Top_10_2010:SubsectionExampleTemplate|XSS|}}
-Preventing injection requires keeping untrusted data separate from commands and queries.
+The application uses untrusted data in the construction of the following HTML snippet without validation or escaping:
+:[[File:Xss-snippet-1.png]]
+The attacker modifies the ‘CC’ parameter in their browser to:
+:[[File:Xss-snippet-2.png]]
+This causes the victim’s session ID to be sent to the attacker’s website, allowing the attacker to hijack the user’s current session.
-#The preferred option is to use a safe API which avoids the use of the interpreter entirely or provides a parameterized interface. Beware of APIs, such as stored procedures, that appear parameterized, but may still allow injection under the hood.
+Note that attackers can also use XSS to defeat any automated CSRF defense the application might employ. See A5 for info on CSRF.
-#If a parameterized API is not available, you should carefully escape special characters using the specific escape syntax for that interpreter. [[ESAPI | OWASP's ESAPI]] has some of these [http://owasp-esapi-java.googlecode.com/svn/trunk_doc/latest/org/owasp/esapi/Encoder.html escaping routines].
-#Positive or "whitelist" input validation with appropriate canonicalization also helps protect against injection, but is '''not''' a complete defense as many applications require special characters in their input. [[ESAPI | OWASP's ESAPI]] has an extensible library of [http://owasp-esapi-java.googlecode.com/svn/trunk_doc/latest/org/owasp/esapi/Validator.html white list input validation routines].
-}}
-{{Top_10_2010:SubsectionExampleTemplate|Injection|}}
-The application uses untrusted data in the construction of the following vulnerable SQL call:
-:<b><span style="color:red;">String query = "SELECT * FROM accounts WHERE custID='" + request.getParameter("id") +"'";</span></b>
-The attacker modifies the 'id' parameter in their browser to send: ' or '1'='1. This changes the meaning of the query to return all the records from the accounts database, instead of only the intended customer's.
-:<b><nowiki>http://example.com/app/accountView?id='</nowiki> or <span style="color: red;">1'='1</span></b>
-In the worst case, the attacker uses this weakness to invoke special stored procedures in the database, allowing a complete takeover of the database host.
-{{Top_10_2010:SubsectionReferencesTemplate|Injection}}
+{{Top_10_2010:SubsectionReferencesTemplate|XSS}}
 {{Top_10_2010:SubSubsectionOWASPReferencesTemplate}}
-* [[SQL_Injection_Prevention_Cheat_Sheet | OWASP SQL Injection Prevention Cheat Sheet]]
+* [[XSS_(Cross_Site_Scripting)_Prevention_Cheat_Sheet | OWASP XSS Prevention Cheat Sheet]]
-* [[Command_Injection | OWASP Injection Flaws Article]]
+* [[Cross-site_Scripting_(XSS) | OWASP Cross-Site Scripting Article]]
+* [[ESAPI | ESAPI Project Home Page]]
 * [http://owasp-esapi-java.googlecode.com/svn/trunk_doc/latest/org/owasp/esapi/Encoder.html ESAPI Encoder API]
-* [http://owasp-esapi-java.googlecode.com/svn/trunk_doc/latest/org/owasp/esapi/Validator.html ESAPI Input Validation API]
+* [http://www.owasp.org/index.php/ASVS#tab=Downloads ASVS: Output Encoding/Escaping Requirements (V6)]
-* [[ASVS#tab=Download | ASVS: Output Encoding/Escaping Requirements (V6)]]
+* [http://www.owasp.org/index.php/ASVS#tab=Downloads ASVS: Input Validation Requirements (V5)]
-* [[Testing_for_SQL_Injection_(OWASP-DV-005) | OWASP Testing Guide: Chapter on SQL Injection Testing]]
+* [[Testing_for_Data_Validation | Testing Guide: 1st 3 Chapters on Data Validation Testing]]
-* [[Reviewing_Code_for_SQL_Injection | OWASP Code Review Guide: Chapter on SQL Injection]]
+* [[Reviewing_Code_for_Cross-site_scripting | OWASP Code Review Guide: Chapter on XSS Review]]
-* [[Reviewing_Code_for_OS_Injection | OWASP Code Review Guide: Command Injection]]
 {{Top_10_2010:SubSubsectionExternalReferencesTemplate}}
-* [http://cwe.mitre.org/data/definitions/77.html CWE Entry 77 on Command Injection]
+* [http://cwe.mitre.org/data/definitions/79.html CWE Entry 79 on Cross-Site Scripting]
-* [http://cwe.mitre.org/data/definitions/89.html CWE Entry 89 on SQL Injection]
+* [http://ha.ckers.org/xss.html RSnake's XSS Attack Cheat Sheet]
-{{Top_10_2010:BottomTemplate|usenext=2010NextLink|next=A2-Cross-Site Scripting (XSS)|useprev=2010PrevLink|prev=Main}}
+{{Top_10_2010:BottomTemplate|useprev=2010PrevLink|usenext=2010NextLink|prev=A1-Injection|next=A3-Broken Authentication and Session Management}}

Difference between pages "Top 10 2010-A1-Injection" and "Top 10 2010-A2-Cross-Site Scripting (XSS)"

Revision as of 15:54, 22 April 2010

Am I Vulnerable to XSS?

How Do I Prevent XSS?

Example Attack Scenarios

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