fopen_wrappers.c in PHP 4.4.0, and possibly other versions, does not properly restrict access to other directories when the open_basedir directive includes a trailing slash, which allows PHP scripts in one directory to access files in other directories whose names are substrings of the original directory.
http://www.vupen.com/english/advisories/2005/2254
http://www.vupen.com/english/advisories/2005/1862
http://www.securityfocus.com/bid/14957
http://www.php.net/release_4_4_1.php
http://www.mandriva.com/security/advisories?name=MDKSA-2005:213
http://www.gentoo.org/security/en/glsa/glsa-200511-08.xml
http://secunia.com/advisories/17557
http://secunia.com/advisories/17510
http://secunia.com/advisories/17371
http://secunia.com/advisories/17229
http://lists.trustix.org/pipermail/tsl-announce/2005-October/000354.html