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Ubuntu Security Notice USN-6611-1
January 29, 2024

exim4 vulnerability

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)

Summary:

Exim could be made to bypass an SPF protection mechanism if it received
a specially crafted request.

Software Description:

• exim4: Exim is a mail transport agent

Details:

It was discovered that Exim incorrectly handled certain requests.
A remote attacker could possibly use a published exploitation technique
to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass
of an SPF protection mechanism.

Update instructions:

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

Ubuntu 23.10:
exim4 4.96-17ubuntu2.2
exim4-base 4.96-17ubuntu2.2
eximon4 4.96-17ubuntu2.2

Ubuntu 22.04 LTS:
exim4 4.95-4ubuntu2.5
exim4-base 4.95-4ubuntu2.5
eximon4 4.95-4ubuntu2.5

Ubuntu 20.04 LTS:
exim4 4.93-13ubuntu1.10
exim4-base 4.93-13ubuntu1.10
eximon4 4.93-13ubuntu1.10

Ubuntu 18.04 LTS (Available with Ubuntu Pro):
exim4 4.90.1-1ubuntu1.10+esm3
exim4-base 4.90.1-1ubuntu1.10+esm3
eximon4 4.90.1-1ubuntu1.10+esm3

Ubuntu 16.04 LTS (Available with Ubuntu Pro):
exim4 4.86.2-2ubuntu2.6+esm6
exim4-base 4.86.2-2ubuntu2.6+esm6
eximon4 4.86.2-2ubuntu2.6+esm6

In general, a standard system update will make all the necessary changes.

References:
https://ubuntu.com/security/notices/USN-6611-1
CVE-2023-51766

Package Information:
https://launchpad.net/ubuntu/+source/exim4/4.96-17ubuntu2.2
https://launchpad.net/ubuntu/+source/exim4/4.95-4ubuntu2.5
https://launchpad.net/ubuntu/+source/exim4/4.93-13ubuntu1.10