Double free vulnerability in the unserializer in PHP 4.4.5 and 4.4.6 allows context-dependent attackers to execute arbitrary code by overwriting variables pointing to (1) the GLOBALS array or (2) the session data in _SESSION. NOTE: this issue was introduced when attempting to patch CVE-2007-1701 (MOPB-31-2007).

PHP 4 before 4.4.5, and PHP 5 before 5.2.1, when register_globals is enabled, allows context-dependent attackers to execute arbitrary code via deserialization of session data, which overwrites arbitrary global variables, as demonstrated by calling session_decode on a string beginning with "_SESSION|s:39:".