Race condition in the symlink function in PHP 5.1.6 and earlier allows local users to bypass the open_basedir restriction by using a combination of symlink, mkdir, and unlink functions to change the file path after the open_basedir check and before the file is opened by the underlying system, as demonstrated by symlinking a symlink into a subdirectory, to point to a parent directory via .. (dot dot) sequences, and then unlinking the resulting symlink.

References

• https://nvd.nist.gov/vuln/detail/CVE-2006-5178
• https://exchange.xforce.ibmcloud.com/vulnerabilities/29340
• http://lists.grok.org.uk/pipermail/full-disclosure/2006-October/049850.html
• http://secunia.com/advisories/22235
• http://secunia.com/advisories/22424
• http://securityreason.com/securityalert/1692
• http://securitytracker.com/id?1016977
• http://www.hardened-php.net/advisory_082006.132.html
• http://www.mandriva.com/security/advisories?name=MDKSA-2006:185
• http://www.neosecurityteam.net/index.php?action=advisories&id=26
• http://www.securityfocus.com/archive/1/447649/100/0/threaded
• http://www.securityfocus.com/archive/1/448020/100/0/threaded
• http://www.securityfocus.com/archive/1/448953/100/0/threaded
• http://www.securityfocus.com/bid/20326
• http://www.turbolinux.com/security/2006/TLSA-2006-38.txt
• http://www.vupen.com/english/advisories/2006/3901