The proc_open function in ext/standard/proc_open.c in PHP before 5.2.11 and 5.3.x before 5.3.1 does not enforce the (1) safe_mode_allowed_env_vars and (2) safe_mode_protected_env_vars directives, which allows context-dependent attackers to execute programs with an arbitrary environment via the env parameter, as demonstrated by a crafted value of the LD_LIBRARY_PATH environment variable.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A7256
http://www.securityfocus.com/bid/37138
http://www.php.net/ChangeLog-5.php
http://www.openwall.com/lists/oss-security/2009/11/23/15
http://www.mandriva.com/security/advisories?name=MDVSA-2009:303
http://www.itrc.hp.com/service/cki/docDisplay.do?docId=emr_na-c02512995
http://svn.php.net/viewvc/?view=revision&revision=286360
http://secunia.com/advisories/41490
http://secunia.com/advisories/41480
http://secunia.com/advisories/40262
http://marc.info/?l=oss-security&m=125897935330618&w=2