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Ubuntu Security Notice USN-6591-2
January 31, 2024

postfix update

A security issue affects these releases of Ubuntu and its derivatives:

• Ubuntu 23.10
• Ubuntu 22.04 LTS
• Ubuntu 20.04 LTS
• Ubuntu 18.04 LTS (Available with Ubuntu Pro)
• Ubuntu 16.04 LTS (Available with Ubuntu Pro)
• Ubuntu 14.04 LTS (Available with Ubuntu Pro)

Summary:

Postfix could allow bypass of email authentication if it received
specially crafted network traffic.

Software Description:

• postfix: High-performance mail transport agent

Details:

USN-6591-1 fixed vulnerabilities in Postfix. A fix with less risk of
regression has been made available since the last update. This update
updates the fix and aligns with the latest configuration guidelines
regarding this vulnerability.

We apologize for the inconvenience.

Original advisory details:

Timo Longin discovered that Postfix incorrectly handled certain email line
endings. A remote attacker could possibly use this issue to bypass an email
authentication mechanism, allowing domain spoofing and potential spamming.

Please note that certain configuration changes are required to address  

this issue. They are not enabled by default for backward compatibility.
Information can be found athttps://www.postfix.org/smtp-smuggling.html.

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 23.10:
postfix 3.8.1-2ubuntu0.2

Ubuntu 22.04 LTS:
postfix 3.6.4-1ubuntu1.3

Ubuntu 20.04 LTS:
postfix 3.4.13-0ubuntu1.4

Ubuntu 18.04 LTS (Available with Ubuntu Pro):
postfix 3.3.0-1ubuntu0.4+esm3

Ubuntu 16.04 LTS (Available with Ubuntu Pro):
postfix 3.1.0-3ubuntu0.4+esm3

Ubuntu 14.04 LTS (Available with Ubuntu Pro):
postfix 2.11.0-1ubuntu1.2+esm3

After a standard system update, you need to set
“smtpd_forbid_bare_newline = normalize” in your configuration and reload
it to make all the necessary changes.

References:
https://ubuntu.com/security/notices/USN-6591-2
https://ubuntu.com/security/notices/USN-6591-1
CVE-2023-51764,https://bugs.launchpad.net/ubuntu/+source/postfix/+bug/2049337,https://bugs.launchpad.net/ubuntu/+source/postfix/+bug/2050834

Package Information:
https://launchpad.net/ubuntu/+source/postfix/3.8.1-2ubuntu0.2
https://launchpad.net/ubuntu/+source/postfix/3.6.4-1ubuntu1.3
https://launchpad.net/ubuntu/+source/postfix/3.4.13-0ubuntu1.4