Important Security Update for Postfix Users

Attention: A new vulnerability has been identified in Postfix (CVE-2023-51764), which may compromise your email server’s security if not addressed!

To all system administrators and IT professionals using Postfix for handling emails, an urgent update is necessary due to a recent security disclosure. Postfix, a widely-used open-source mail transfer agent that helps in routing and delivering electronic mail, is currently at risk of SMTP smuggling if not configured with certain settings.

The CVE identified (CVE-2023-51764) has a medium severity score of 5.3. It exposes a security loophole in versions up to 3.8.5, which can allow attackers to inject spoofed email messages that bypass SPF protection mechanisms. SPF, or Sender Policy Framework, is a path verification system that prevents spam by detecting email spoofing.

The vulnerability manipulates how line terminations are handled, specifically instances of line-feeds () followed by a carriage-return and line-feed sequence (). This mismatch in protocols between Postfix and other popular email servers creates an opportunity for attackers aiming to misuse the email communication system.

To secure your systems against this vulnerability, it is recommended to update to at least one of these Postfix versions: 3.5.23, 3.6.13, 3.7.9, 3.8.4, or 3.9. Additionally, configuring your Postfix server with the setting `smtpd_data_restrictions=reject_unauth_pipelining` and `smtpd_discard_ehlo_keywords=chunking` will further restrain unauthorized email injections.

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