USN-8540-1: OpenVPN vulnerabilities

It was discovered that OpenVPN had a 1-byte buffer overrun when handling
NTLMv2 proxy responses. An attacker could use this issue to cause a denial
of service or possibly execute arbitrary code. This issue only affected
Ubuntu 24.04 LTS and Ubuntu 26.04 LTS. (CVE-2026-11771)

It was discovered that OpenVPN incorrectly handled metadata when extracting
tls-crypt-v2 client keys. An attacker could possibly use this issue to
obtain sensitive information. (CVE-2026-12932)

It was discovered that OpenVPN had a use-after-free in the ack_write_buf
handling. An attacker could use this issue to cause OpenVPN to crash,
resulting in a denial of service, or possibly execute arbitrary code.
(CVE-2026-12996)

It was discovered that OpenVPN had a use-after-free in the tls_wrap_reneg
handling. An attacker could use this issue to cause OpenVPN to crash,
resulting in a denial of service, or possibly execute arbitrary code. This
issue only affected Ubuntu 24.04 LTS and Ubuntu 26.04 LTS. (CVE-2026-13117)

It was discovered that OpenVPN incorrectly validated authentication tokens
when external authentication was enabled. A remote attacker could possibly
use this issue to cause OpenVPN to crash, resulting in a denial of service.
This issue only affected Ubuntu 24.04 LTS and Ubuntu 26.04 LTS.
(CVE-2026-13122)

It was discovered that OpenVPN had a memory leak when handling tls-crypt-v2
client keys. A remote attacker with a valid tls-crypt-v2 client key could
possibly use this issue to cause OpenVPN to consume excessive resources,
leading to a denial of service. (CVE-2026-13698)