[USN-7542-1] Kerberos vulnerability

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Ubuntu Security Notice USN-7542-1
May 28, 2025

krb5 vulnerability
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 24.04 LTS
- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS
- Ubuntu 14.04 LTS

Summary:

Kerberos could be made to expose sensitive information over the network.

Software Description:
- krb5: MIT Kerberos Network Authentication Protocol

Details:

It was discovered that Kerberos allowed the usage of weak cryptographic
standards. An attacker could possibly use this issue to expose sensitive
information.

This update introduces the allow_rc4 and allow_des3 configuration options,
and disables the usage of RC4 and 3DES ciphers by default. Users are
advised to discontinue their usage and upgrade to stronger encryption
protocols. If the use of the insecure RC4 and 3DES algorithms is necessary,
they can be enabled with the aforementioned configuration options.

Update instructions:

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

Ubuntu 24.04 LTS
libk5crypto3 1.20.1-6ubuntu2.6
libkrb5-3 1.20.1-6ubuntu2.6

Ubuntu 22.04 LTS
libk5crypto3 1.19.2-2ubuntu0.7
libkrb5-3 1.19.2-2ubuntu0.7

Ubuntu 20.04 LTS
libk5crypto3 1.17-6ubuntu4.11
libkrb5-3 1.17-6ubuntu4.11

Ubuntu 18.04 LTS
libk5crypto3 1.16-2ubuntu0.4+esm5
Available with Ubuntu Pro
libkrb5-3 1.16-2ubuntu0.4+esm5
Available with Ubuntu Pro

Ubuntu 16.04 LTS
libk5crypto3 1.13.2+dfsg-5ubuntu2.2+esm7
Available with Ubuntu Pro
libkrb5-3 1.13.2+dfsg-5ubuntu2.2+esm7
Available with Ubuntu Pro

Ubuntu 14.04 LTS
libk5crypto3 1.12+dfsg-2ubuntu5.4+esm7
Available with Ubuntu Pro
libkrb5-3 1.12+dfsg-2ubuntu5.4+esm7
Available with Ubuntu Pro

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

References:
https://ubuntu.com/security/notices/USN-7542-1
CVE-2025-3576

Package Information:
https://launchpad.net/ubuntu/+source/krb5/1.20.1-6ubuntu2.6
https://launchpad.net/ubuntu/+source/krb5/1.19.2-2ubuntu0.7
https://launchpad.net/ubuntu/+source/krb5/1.17-6ubuntu4.11