Failure to Handle URL Encoding (Hex Encoding)
Weakness ID: 177 (Weakness Variant)Status: Draft
+ Description

Description Summary

The software does not properly handle when all or part of an input has been URL encoded.
+ Time of Introduction
  • Implementation
+ Applicable Platforms



+ Observed Examples
CVE-2000-0900Hex-encoded path traversal variants - "%2e%2e", "%2e%2e%2f", "%5c%2e%2e"
CVE-2005-2256Hex-encoded path traversal variants - "%2e%2e", "%2e%2e%2f", "%5c%2e%2e"
CVE-2004-2121Hex-encoded path traversal variants - "%2e%2e", "%2e%2e%2f", "%5c%2e%2e"
CVE-2004-0280"%20" (encoded space)
CVE-2003-0424"%20" (encoded space)
CVE-2001-0693"%20" (encoded space)
CVE-2001-0778"%20" (encoded space)
CVE-2002-1831Crash via hex-encoded space "%20".
CVE-2000-0671"%00" (encoded null)
CVE-2004-0189"%00" (encoded null)
CVE-2002-1291"%00" (encoded null)
CVE-2002-1031"%00" (encoded null)
CVE-2001-1140"%00" (encoded null)
CVE-2004-0760"%00" (encoded null)
CVE-2002-1025"%00" (encoded null)
CVE-2002-1213"%2f" (encoded slash)
CVE-2004-0072"%5c" (encoded backslash) and "%2e" (encoded dot) sequences
CVE-2004-0847"%5c" (encoded backslash)
CVE-2002-1575"%0a" (overlaps CRLF)
+ Potential Mitigations

Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.

Phase: Architecture and Design

Assume all input is malicious. Use a standard input validation mechanism to validate all input for length, type, syntax, and business rules before accepting the data to be displayed or stored. Use an "accept known good" validation strategy.

Use and specify a strong output encoding (such as ISO 8859-1 or UTF 8).

Do not rely exclusively on blacklist validation to detect malicious input or to encode output. There are too many variants to encode a character; you're likely to miss some variants.

Inputs should be decoded and canonicalized to the application's current internal representation before being validated. Make sure that your application does not decode the same input twice. Such errors could be used to bypass whitelist schemes by introducing dangerous inputs after they have been checked.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class172Encoding Error
Development Concepts (primary)699
Research Concepts (primary)1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERURL Encoding (Hex Encoding)
+ Related Attack Patterns
CAPEC-IDAttack Pattern Name
(CAPEC Version: 1.4)
64Using Slashes and URL Encoding Combined to Bypass Validation Logic
72URL Encoding
+ Content History
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Potential Mitigations, Time of Introduction
Suggested OWASP Top Ten 2004 mapping
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Observed Example, Taxonomy Mappings
2009-07-27CWE Content TeamMITREInternal
updated Potential Mitigations
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11URL Encoding (Hex Encoding)