CWE-626 Detail

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

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.

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.

Modes Of Introduction

Implementation

Applicable Platforms

Language

Name: PHP (Undetermined)
Name: Perl (Undetermined)
Name: ASP.NET (Undetermined)

Common Consequences

Observed Examples

Potential Mitigations

Phases : Implementation
Remove null bytes from all incoming strings.

Vulnerability Mapping Notes

Justification : This CWE entry is at the Variant level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Comment : Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

NotesNotes

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

References

REF-514

Poison NULL byte
Rain Forest Puppy.
https://insecure.org/news/P55-07.txt

REF-515

0x00 vs ASP file upload scripts
Brett Moore.
http://www.security-assessment.com/Whitepapers/0x00_vs_ASP_File_Uploads.pdf

REF-516

ShAnKaR: multiple PHP application poison NULL byte vulnerability
ShAnKaR.
https://seclists.org/fulldisclosure/2006/Sep/185

Submission

Modifications