Software Engineering Institute

Postfix is an mail transport agent (MTA) that is used by several Unix-like operating systems. Symbolic links and hard links are types of files that reference other files. Unlike hard links, symbolic links can point to directories and use relative pathnames.

On some non-POSIX.1-2001 and X/Open XPG4v2 compliant systems, users can hardlink symlinks which are owned by the root user. Postfix allows root-owned symlinks to be used as a mail destination folder. A hard link to a Postfix root-owned symlink could point to a file that can be overwritten by Postfix, regardless of the permissions of the destination file.

A local, authenticated attacker may be able to overwrite arbitrary files, possibly gaining elevated privileges.

Upgrade
See http://article.gmane.org/gmane.mail.postfix.announce/110 for information about obtaining updated software. Users who do not compile Postfix from source should see the systems affected section below for a partial list of affected vendors.

Set mailbox permissions

Making the system mail spool directory root-owned may mitigate this vulnerability. See http://article.gmane.org/gmane.mail.postfix.announce/110 for specific information about this and other workarounds.