Libcontainer and Docker Engine before 1.6.1 opens the file-descriptor passed to the pid-1 process before performing the chroot, which allows local users to gain privileges via a symlink attack in an image.

References

• https://nvd.nist.gov/vuln/detail/CVE-2015-3627
• moby/moby@d5ebb60
• https://groups.google.com/forum/#!searchin/docker-user/1.6.1/docker-user/47GZrihtr-4/nwgeOOFLexIJ
• https://groups.google.com/forum/#%21searchin/docker-user/1.6.1/docker-user/47GZrihtr-4/nwgeOOFLexIJ
• https://lists.opensuse.org/opensuse-updates/2015-05/msg00023.html
• https://packetstormsecurity.com/files/131835/Docker-Privilege-Escalation-Information-Disclosure.html
• https://seclists.org/fulldisclosure/2015/May/28