CWE

Common Weakness Enumeration

A Community-Developed Dictionary of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors Common Weakness Scoring System
Common Weakness Risk Analysis Framework
Home > CWE List > CWE- Individual Dictionary Definition (2.6)  

Presentation Filter:

CWE-86: Improper Neutralization of Invalid Characters in Identifiers in Web Pages

 
Improper Neutralization of Invalid Characters in Identifiers in Web Pages
Weakness ID: 86 (Weakness Variant)Status: Draft
+ Description

Description Summary

The software does not neutralize or incorrectly neutralizes invalid characters or byte sequences in the middle of tag names, URI schemes, and other identifiers.

Extended Description

Some web browsers may remove these sequences, resulting in output that may have unintended control implications. For example, the software may attempt to remove a "javascript:" URI scheme, but a "java%00script:" URI may bypass this check and still be rendered as active javascript by some browsers, allowing XSS or other attacks.

+ Time of Introduction
  • Implementation
+ Applicable Platforms

Languages

All

+ Common Consequences
ScopeEffect
Confidentiality
Integrity
Availability

Technical Impact: Read application data; Execute unauthorized code or commands

+ Observed Examples
ReferenceDescription
CVE-2004-0595XSS filter doesn't filter null characters before looking for dangerous tags, which are ignored by web browsers. Multiple Interpretation Error (MIE) and validate-before-cleanse.
+ Potential Mitigations

Phase: Implementation

Strategy: Output Encoding

Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component.

The problem of inconsistent output encodings often arises in web pages. If an encoding is not specified in an HTTP header, web browsers often guess about which encoding is being used. This can open up the browser to subtle XSS attacks.

Phase: Implementation

Strategy: Identify and Reduce Attack Surface

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 more recent versions of Internet Explorer and Firefox), this attribute can prevent the user's session cookie from being accessible to malicious client-side scripts that use document.cookie. This is not a complete solution, since HttpOnly is not supported by all browsers. More importantly, XMLHTTPRequest and other powerful browser technologies provide read access to HTTP headers, including the Set-Cookie header in which the HttpOnly flag is set.

Effectiveness: Defense in Depth

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness BaseWeakness Base79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfWeakness BaseWeakness Base436Interpretation Conflict
Research Concepts1000
ChildOfCategoryCategory896SFP Cluster: Tainted Input
Software Fault Pattern (SFP) Clusters (primary)888
PeerOfWeakness BaseWeakness Base184Incomplete Blacklist
Research Concepts1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERInvalid Characters in Identifiers
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Description, Name, Relationships, Other_Notes, Taxonomy_Mappings
2009-10-29CWE Content TeamMITREInternal
updated Description, Other_Notes
2010-04-05CWE Content TeamMITREInternal
updated Description, Name, Related_Attack_Patterns
2010-06-21CWE Content TeamMITREInternal
updated Potential_Mitigations
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2012-05-11CWE Content TeamMITREInternal
updated Related_Attack_Patterns, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
Previous Entry Names
Change DatePrevious Entry Name
2008-09-09Invalid Characters in Identifiers
2010-04-05Failure to Sanitize Invalid Characters in Identifiers in Web Pages
Page Last Updated: February 18, 2014