A critical security update addresses multiple OpenVPN vulnerabilities, including a buffer overrun in NTLMv2 proxy handling (CVE-2026-11771), two use-after-free flaws in ack_write_buf and tls_wrap_reneg handling (CVE-2026-12996, CVE-2026-13117), an information disclosure in tls-crypt-v2 key extraction (CVE-2026-12932), a denial of service via invalid authentication tokens (CVE-2026-13122), and a resource exhaustion memory leak with tls-crypt-v2 keys (CVE-2026-13698). Several of these issues, which can lead to denial of service, information disclosure, or arbitrary code execution, specifically affect Ubuntu 24.04 LTS and Ubuntu 26.04 LTS. Administrators should apply the relevant distribution security patches immediately.
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)