CVE-2026-42009
It was discovered that GnuTLS had a timing side-channel when processing malformed ciphertexts in RSA-PSK ClientKeyExchange. A remote attacker could possibly use this issue to recover sensitive information. This issue only affected Ubuntu 18.04 LTS. (CVE-2024-0553) Bing Shi discovered that GnuTLS incorrectly handled decoding certain DER-encoded certificates. A remote attacker could possibly use this issue to cause GnuTLS to consume resources, leading to a denial of service. This issue only affected Ubuntu 18.04 LTS. (CVE-2024-12243) Luigino Camastra discovered that GnuTLS incorrectly handled certain PKCS11 token labels. A remote attacker could use this issue to cause GnuTLS to crash, resulting in a denial of service, or possibly execute arbitrary code. The default compiler options for affected releases should reduce the vulnerability to a denial of service. (CVE-2025-9820) Tim Scheckenbach discovered that GnuTLS incorrectly handled malicious certificates containing a large number of name constraints and subject alternative names. A remote attacker could possibly use this issue to cause GnuTLS to consume resources, resulting in a denial of service. This issue only affected Ubuntu 18.04 LTS and Ubuntu 20.04 LTS. (CVE-2025-14831) Oleh Konko and Joshua Rogers discovered that GnuTLS did not properly handle case-insensitive name constraints in certain cases. A remote attacker could possibly use this issue to bypass certificate validation, leading to a machine-in-the-middle attack. (CVE-2026-3833) Joshua Rogers discovered that GnuTLS did not properly handle very short premaster secrets in certain RSA key exchange cases with PKCS#11-backed server keys. A remote attacker could possibly use this issue to obtain sensitive information. This issue only affected Ubuntu 18.04 LTS and Ubuntu 20.04 LTS. (CVE-2026-5260) Joshua Rogers discovered that GnuTLS did not properly handle malformed DTLS handshake fragments in certain cases. A remote attacker could possibly use this issue to ob
CSIRTS triage
- What
- Multiple vulnerabilities could lead to information disclosure, denial of service, or arbitrary code execution.
- Who is affected
- Users of GnuTLS on Ubuntu 18.04 LTS.
- Urgency
- Remediation is important due to the severity of the vulnerabilities.
- Action
- Apply the latest security updates for GnuTLS.
AI-assisted analysis generated from the source advisory — verify against the original.
⚡ Watch CVE-2026-42009
Get an email if CVE-2026-42009 is added to CISA KEV, gains public exploit code, or a new advisory cites it — max one per day, one-click unsubscribe.
Exploitation outlook
- Moderate exploitation risk1.3% 30-day exploitation probability. Patch within normal cadence, watch for KEV listing. Riskier than 68% of all EPSS-scored CVEs.
Advisory coverage (2)
- high[UPDATE] [high] GnuTLS: Multiple vulnerabilitiescert-bund · 2026-07-10
- unknownUSN-8502-1: GnuTLS vulnerabilitiesubuntu · 2026-07-06
External references
Embed the live status
— this badge updates automatically when the KEV or exploit status changes. How to embed it →
[](https://www.csirts.com/cve/CVE-2026-42009)