Null Byte Interaction Error (Poison Null Byte)
Weakness ID: 626 (Weakness Variant)Status: Draft
+ Description

Description Summary

The product does not properly handle null bytes or NUL characters when passing data between different representations or components.

Extended Description

A null byte (NUL character) can have different meanings across representations or languages. For example, it is a string terminator in standard C libraries, but Perl and PHP strings do not treat it as a terminator. When two representations are crossed - such as when Perl or PHP invokes underlying C functionality - this can produce an interaction error with unexpected results. Similar issues have been reported for ASP. Other interpreters written in C might also be affected.

+ Time of Introduction
  • Implementation
+ Applicable Platforms





+ Observed Examples
CVE-2005-4155NUL byte bypasses PHP regular expression check
CVE-2005-3153inserting SQL after a NUL byte bypasses whitelist regexp, enabling SQL injection
+ Potential Mitigations

Remove null bytes from all incoming strings

+ Other Notes

The poison null byte is frequently useful in path traversal attacks by terminating hard-coded extensions that are added to a filename. It can play a role in regular expression processing in PHP.

There are not many CVE examples, because the poison NULL byte is (1) a design limitation, which typically is not included in CVE by itself; and (2) it is typically used as a facilitator manipulation to widen the scope of potential attacks against other vulnerabilities.

Current (2007) usage of "poison null byte" is typically related to this C/Perl/PHP interaction error, but the original term in 1998 was applied to an off-by-one buffer overflow involving a null byte.

+ Weakness Ordinalities
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class20Improper Input Validation
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfWeakness BaseWeakness Base436Interpretation Conflict
Development Concepts699
Research Concepts1000
+ References
Rain Forest Puppy. "Poison NULL byte". Phrack 55. <>.
Brett Moore. "0x00 vs ASP file upload scripts". <>.
ShAnKaR. "ShAnKaR: multiple PHP application poison NULL byte vulnerability". <>.
+ Content History
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time of Introduction
2008-09-08CWE Content TeamMITREInternal
updated Applicable Platforms, Description, Relationships, Observed Example, Other Notes, Weakness Ordinalities