CVE-2020-14396: 
NixOS vulnerability analysis and mitigation

An issue was discovered in LibVNCServer before version 0.9.13 where libvncclient/tls_openssl.c had a NULL pointer dereference vulnerability. The vulnerability was discovered and disclosed on June 17, 2020 (NVD, CVE).

The vulnerability occurs in the TLS handling code specifically in libvncclient/tls_openssl.c where a NULL pointer is dereferenced during anonymous TLS connections. The issue happens in anonTLS mode where the credential pointer (cred) is NULL but is still accessed (GitHub Commit). The vulnerability has a CVSS v3 severity score of 7.5 (High) (Ubuntu).

If exploited, this vulnerability could cause LibVNCServer to crash, resulting in a denial of service condition. The issue specifically affects systems running LibVNCServer in configurations that use anonymous TLS connections (Ubuntu Notice).

The vulnerability can be triggered remotely by an attacker during the TLS connection setup process when anonymous TLS mode is enabled. The issue requires no special privileges or user interaction to exploit (NVD).

The vulnerability was fixed in LibVNCServer version 0.9.13. Users should upgrade to this version or later to address the issue. For Ubuntu systems, security updates were released for Ubuntu 20.04 LTS (libvncclient1 - 0.9.12+dfsg-9ubuntu0.2), Ubuntu 18.04 LTS, and Ubuntu 16.04 LTS. After updating, all LibVNCServer applications need to be restarted to apply the changes (Ubuntu Notice).