Improper Sanitization of Script-Related HTML Tags in a Web Page (Basic XSS)
Weakness ID: 80 (Weakness Variant)Status: Incomplete
+ Description

Description Summary

The software receives input from an upstream component, but it does not sanitize or incorrectly sanitizes special characters such as "<", ">", and "&" that could be interpreted as web-scripting elements when they are sent to a downstream component that processes web pages.

Extended Description

This may allow such characters to be treated as control characters, which are executed client-side in the context of the user's session. Although this can be classified as an injection problem, the more pertinent issue is the failure to convert such special characters to respective context-appropriate entities before displaying them to the user.

+ Time of Introduction
  • Implementation
+ Applicable Platforms

Languages

All

+ Likelihood of Exploit

High to Very High

+ Demonstrative Examples

Example 1

In the following example, a guestbook comment isn't properly sanitized for script-related tags before being displayed in a client browser.

(Bad Code)
Example Language: JSP 
<% for (Iterator i = guestbook.iterator(); i.hasNext(); ) {
Entry e = (Entry) i.next(); %>
<p>Entry #<%= e.getId() %></p>
<p><%= e.getText() %></p>
<%
} %>
+ Observed Examples
ReferenceDescription
CVE-2002-0938XSS in parameter in a link.
CVE-2002-1495XSS in web-based email product via attachment filenames.
CVE-2003-1136HTML injection in posted message.
CVE-2004-2171XSS not quoted in error page.
+ Potential Mitigations

Carefully check each input parameter against a rigorous positive specification (white list) defining the specific characters and format allowed. All input should be sanitized, not just parameters that the user is supposed to specify, but all data in the request, including hidden fields, cookies, headers, the URL itself, and so forth. A common mistake that leads to continuing XSS vulnerabilities is to validate only fields that are expected to be redisplayed by the site. We often encounter data from the request that is reflected by the application server or the application that the development team did not anticipate. Also, a field that is not currently reflected may be used by a future developer. Therefore, validating ALL parts of the HTTP request is recommended.

This involves "HTML Entity Encoding" all non-alphanumeric characters from data that was received from the user and is now being written to the request.

With Struts, you should write all data from form beans with the bean's filter attribute set to true.

Additionally, to help mitigate XSS attacks against the user's session cookie, set the session cookie to be HttpOnly. In browsers that support the HttpOnly feature (such as Internet Explorer), this attribute prevents the user's session cookie from being accessed by client-side scripts, including scripts inserted due to a XSS attack.

+ Weakness Ordinalities
OrdinalityDescription
Primary
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness BaseWeakness Base79Failure to Preserve Web Page Structure ('Cross-site Scripting')
Development Concepts (primary)699
Research Concepts (primary)1000
MemberOfViewView630Weaknesses Examined by SAMATE
Weaknesses Examined by SAMATE (primary)630
+ Causal Nature

Explicit

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERBasic XSS
+ Related Attack Patterns
CAPEC-IDAttack Pattern Name
(CAPEC Version: 1.4)
18Embedding Scripts in Nonscript Elements
+ White Box Definitions

A weakness where the code path has:

1. start statement that accepts input from HTML page

2. end statement that publishes a data item to HTML where

a. the input is part of the data item and

b. the input contains XSS syntax

+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Sean EidemillerCigitalExternal
added/updated demonstrative examples
2008-07-01Eric DalciCigitalExternal
updated Time of Introduction
2008-08-01KDM AnalyticsExternal
added/updated white box definitions
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Taxonomy Mappings, Weakness Ordinalities
2008-10-14CWE Content TeamMITREInternal
updated Description
2009-05-27CWE Content TeamMITREInternal
updated Demonstrative Examples, Description, Name
2009-07-17KDM AnalyticsExternal
Improved the White Box Definition
2009-07-27CWE Content TeamMITREInternal
updated White Box Definitions
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Basic XSS
2009-05-27Failure to Sanitize Script-Related HTML Tags in a Web Page (Basic XSS)
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