Postfix is a Mail Transport Agent , supporting LDAP, SMTP AUTH , 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. Red Hat would like to thank the CERT/CC for reporting CVE-2011-0411. The CERT/CC acknowledges Wietse Venema as the original reporter. Users of Postfix are advised to upgrade to these updated packages, which contain a backported patch to resolve this issue. After installing this update, the postfix service will be restarted automatically.