Ubuntu Security Notice USN-5034-2
August 10, 2021

c-ares vulnerability

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

- Ubuntu 16.04 ESM


c-ares could be made to return wrong domains.

Software Description:
- c-ares: library for asynchronous name resolution


USN-5034-1 fixed a vulnerability in c-ares. This update provides
the corresponding update for Ubuntu 16.04 ESM.

Original advisory details:

 Philipp Jeitner and Haya Shulman discovered that c-ares incorrectly
 validated certain hostnames returned by DNS servers. A remote attacker
 could possibly use this issue to perform Domain Hijacking attacks.

Update instructions:

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

Ubuntu 16.04 ESM:
  libc-ares2                      1.10.0-3ubuntu0.2+esm1

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