Directory traversal vulnerability in the posix_access function in PHP 5.2.6 and earlier allows remote attackers to bypass safe_mode restrictions via a .. (dot dot) in an http URL, which results in the URL being canonicalized to a local filename after the safe_mode check has successfully run.
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.