Interpretation Conflict
Weakness ID: 436 (Weakness Base)Status: Incomplete
+ Description

Description Summary

Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.

Extended Description

This is generally found in proxies, firewalls, anti-virus software, and other intermediary devices that allow, deny, or modify traffic based on how the client or server is expected to behave.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms



+ Observed Examples
CVE-2005-1215Bypass filters or poison web cache using requests with multiple Content-Length headers, a non-standard behavior.
CVE-2002-0485Anti-virus product allows bypass via Content-Type and Content-Disposition headers that are mixed case, which are still processed by some clients.
CVE-2002-1978FTP clients sending a command with "PASV" in the argument can cause firewalls to misinterpret the server's error as a valid response, allowing filter bypass.
CVE-2002-1979FTP clients sending a command with "PASV" in the argument can cause firewalls to misinterpret the server's error as a valid response, allowing filter bypass.
CVE-2002-0637Virus product bypass with spaces between MIME header fields and the ":" separator, a non-standard message that is accepted by some clients.
CVE-2002-1777AV product detection bypass using inconsistency manipulation (file extension in MIME Content-Type vs. Content-Disposition field).
CVE-2005-3310CMS system allows uploads of files with GIF/JPG extensions, but if they contain HTML, Internet Explorer renders them as HTML instead of images.
CVE-2005-4260Interpretation conflict allows XSS via invalid "<" when a ">" is expected, which is treated as ">" by many web browsers.
CVE-2005-4080Interpretation conflict (non-standard behavior) enables XSS because browser ignores invalid characters in the middle of tags.
+ Other Notes

The classic multiple interpretation flaws were reported in a paper that described the limitations of intrusion detection systems. Ptacek and Newsham (see references below) showed that OSes varied widely in their behavior with respect to unusual network traffic, which made it difficult or impossible for intrusion detection systems to properly detect certain attacker manipulations that took advantage of the OS differences. Another classic multiple interpretation error is the "poison null byte" described by Rain Forest Puppy (see reference below), in which null characters have different interpretations in Perl and C, which have security consequences when Perl invokes C functions. Similar problems have been reported in ASP (see ASP reference below) and PHP. Some of the more complex web-based attacks, such as HTTP request smuggling, also involve multiple interpretation errors.

A comment on a way to manage these problems is in David Skoll in the reference below.

Manipulations are major factors in multiple interpretation errors, such as doubling, inconsistencies between related fields, and whitespace.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class435Interaction Error
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant86Failure to Sanitize Invalid Characters in Identifiers in Web Pages
Research Concepts1000
ParentOfWeakness BaseWeakness Base115Misinterpretation of Input
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base437Incomplete Model of Endpoint Features
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base444Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling')
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant626Null Byte Interaction Error (Poison Null Byte)
Development Concepts699
Research Concepts1000
ParentOfWeakness VariantWeakness Variant650Trusting HTTP Permission Methods on the Server Side
Research Concepts (primary)1000
PeerOfWeakness BaseWeakness Base351Insufficient Type Distinction
Research Concepts1000
PeerOfWeakness BaseWeakness Base434Unrestricted Upload of File with Dangerous Type
Research Concepts1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERMultiple Interpretation Error (MIE)
WASC27HTTP Response Smuggling
+ Related Attack Patterns
CAPEC-IDAttack Pattern Name
(CAPEC Version: 1.4)
33HTTP Request Smuggling
105HTTP Request Splitting
+ References
Steve Christey. "On Interpretation Conflict Vulnerabilities". Bugtraq. 2005-11-03.
Thomas H. Ptacek and Timothy N. Newsham. "Insertion, Evasion, and Denial of Service: Eluding Network Intrusion Detection". January 1998. <>.
Brett Moore. "0x00 vs ASP file upload scripts". 2004-07-13. <>.
Rain Forest Puppy. "Poison NULL byte". Phrack.
David F. Skoll. "Re: Corsaire Security Advisory - Multiple vendor MIME RFC2047 encoding". Bugtraq. 2004-09-15. <>.
+ Content History
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time of Introduction
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Other Notes, Taxonomy Mappings
2008-10-14CWE Content TeamMITREInternal
updated Description
2009-05-27CWE Content TeamMITREInternal
updated Related Attack Patterns
2009-10-29CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Multiple Interpretation Error (MIE)