USN-8710-1: libevent vulnerabilities

Alexis Challande discovered that libevent incorrectly handled certain empty output buffers. An attacker could possibly use this issue to trigger a use-after-free, resulting in a denial of service or arbitrary code execution. This issue only affected Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 26.04 LTS.