Postfix before 2.3.15, 2.4 before 2.4.8, 2.5 before 2.5.4, and 2.6 before 2.6-20080814, when the operating system supports hard links to symlinks, allows local users to append e-mail messages to a file to which a root-owned symlink points, by creating a hard link to this symlink and then sending a message. NOTE: this can be leveraged to gain privileges if there is a symlink to an init script.

Postfix 2.5 before 2.5.4 and 2.6 before 2.6-20080814 delivers to a mailbox file even when this file is not owned by the recipient, which allows local users to read e-mail messages by creating a mailbox file corresponding to another user's account name.

A heap-based buffer overread flaw was found in the way Postfix mail transport agent performed SASL handlers management for SMTP sessions, when the Cyrus SASL authentication was enabled. A remote attacker could use this flaw to cause Postfix smtpd server crash via specially-crafted SASL authentication request.

Note: The default configuration of Postfix mail transport agent, as shipped with Red Hat Enterprise Linux 4, 5, and 6 do not enable SASL support for SMTP authentication for mail clients (thus Postfix server instances using it are not vulnerable to this flaw).

Workaround: If your Postfix server configuration contains directive like:

smtpdsaslauthenable = yes

change 'yes' to 'no' or comment the whole line out not to be vulnerable to this flaw.

The STARTTLS implementation in Postfix 2.4.x before 2.4.16, 2.5.x before 2.5.12, 2.6.x before 2.6.9, and 2.7.x before 2.7.3 does not properly restrict I/O buffering, which allows man-in-the-middle attackers to insert commands into encrypted SMTP sessions by sending a cleartext command that is processed after TLS is in place, related to a "plaintext command injection" attack.