Updated postfix packages that fix two security issues are now available for Red Hat Enterprise Linux 4 and 5.
The Red Hat Security Response Team has rated this update as having moderate security impact. Common Vulnerability Scoring System (CVSS) base scores, which give detailed severity ratings, are available for each vulnerability from the CVE links in the References section.
Postfix is a Mail Transport Agent (MTA), supporting LDAP, SMTP AUTH (SASL), and TLS.
It was discovered that Postfix did not flush the received SMTP commands buffer after switching to TLS encryption for an SMTP session. A man-in-the-middle attacker could use this flaw to inject SMTP commands into a victim's session during the plain text phase. This would lead to those commands being processed by Postfix after TLS encryption is enabled, possibly allowing the attacker to steal the victim's mail or authentication credentials. (CVE-2011-0411)
It was discovered that Postfix did not properly check the permissions of users' mailbox files. A local attacker able to create files in the mail spool directory could use this flaw to create mailbox files for other local users, and be able to read mail delivered to those users. (CVE-2008-2937)
Red Hat would like to thank the CERT/CC for reporting CVE-2011-0411, and Sebastian Krahmer of the SuSE Security Team for reporting CVE-2008-2937. The CERT/CC acknowledges Wietse Venema as the original reporter of CVE-2011-0411.
Users of Postfix are advised to upgrade to these updated packages, which contain backported patches to resolve these issues. After installing this update, the postfix service will be restarted automatically.