CWE-626 Null Byte Interaction Error (Poison Null Byte)

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.

• Integrity: Unexpected State

• [Implementation] Remove null bytes from all incoming strings.

• Automated Static Analysis: Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

• CVE-2005-4155: NUL byte bypasses PHP regular expression check • CVE-2005-3153: inserting SQL after a NUL byte bypasses allowlist regexp, enabling SQL injection