The postfix.postinst script in the Debian GNU/Linux and Ubuntu postfix 2.5.5 package grants the postfix user write access to /var/spool/postfix/pid, which might allow local users to conduct symlink attacks that overwrite arbitrary files.

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.

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.