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Weakness (CWE)

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

Variant Draft

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

More detail

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.

How to prevent it (1 mitigation)

  1. Implementation

    Remove null bytes from all incoming strings.

Source: MITRE CWE-626

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    CVE-2019-17137 Public exploit

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