The product does not properly handle null bytes or NUL characters when passing data between different representations or components.
View on MITREA 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.
Remove null bytes from all incoming strings.
No detection method information available for this CWE.
inserting SQL after a NUL byte bypasses allowlist regexp, enabling SQL injection
View DetailsCWE-626: Null Byte Interaction Error (Poison Null Byte) is a Common Weakness Enumeration (CWE) entry maintained by MITRE. 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.
If exploited, CWE-626 (Null Byte Interaction Error (Poison Null Byte)) it can compromise Integrity, leading to outcomes such as Unexpected State.
Recommended mitigations for CWE-626 include: Remove null bytes from all incoming strings.
CWE-626 commonly affects PHP, Perl and ASP.NET. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.
MITRE documents real CVEs mapped to CWE-626, including CVE-2005-4155 and CVE-2005-3153. You can look up the full details of each CVE, including CVSS scores and remediation guidance, on our CVE Lookup tool.
A CWE (Common Weakness Enumeration) like CWE-626 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.