USN-8502-1: GnuTLS vulnerabilities

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 obtain sensitive information, or cause a
denial of service. This issue only affected Ubuntu 20.04 LTS.
(CVE-2026-33845)

Haruto Kimura, Oscar Reparaz, and Zou Dikai discovered that GnuTLS did
not properly validate DTLS handshake fragment lengths in certain cases.
A remote attacker could possibly use this issue to cause GnuTLS to
crash, resulting in a denial of service, or execute arbitrary code.
(CVE-2026-33846)

Joshua Rogers discovered that GnuTLS did not properly order DTLS packets
with duplicate sequence numbers in certain cases. A remote attacker
could possibly use this issue to cause GnuTLS to crash, resulting in a
denial of service. (CVE-2026-42009)

Joshua Rogers discovered that GnuTLS did not properly handle usernames
containing NUL characters in certain RSA-PSK configurations. A remote
attacker could possibly use this issue to bypass authentication and gain
unintended access to services. This issue only affected Ubuntu 20.04
LTS. (CVE-2026-42010)