The PHP Group Information for VU#903934

Hash table implementations vulnerable to algorithmic complexity attacks



Vendor Statement

No statement is currently available from the vendor regarding this vulnerability.

Vendor Information

According to the n.runs AG advisory:
"PHP 5 uses the DJBX33A (Dan Bernstein's times 33, addition) hash function and parses POST form data into the $_POST hash table. Because of the structure of the hash function, it is vulnerable to an equivalent substring attack."

From the Workarounds section:
"The easiest way to reduce the impact of such an attack is to reduce the CPU time that a request is allowed to take. For PHP, this can be configured using the max_input_time parameter."

PHP 5.4.0 RC4 has been released which adds a max_input_vars directive to help mitigate hash collision attacks. Please note that this is a release candidate, not a stable release.

Vendor References


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