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GnuTLS CVE-2026-42009

| EUVDEUVD-2026-30769 HIGH
Undefined Behavior for Input to API (CWE-475)
2026-05-18 secalert@redhat.com GHSA-9gx7-g5hv-xjjj
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7.5
CVSS 3.1 · Vendor: redhat
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Severity by source

Vendor (redhat) PRIMARY
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
SUSE
HIGH
qualitative
Red Hat
7.5 HIGH
qualitative

Primary rating from Vendor (redhat).

CVSS VectorVendor: redhat

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

1
Analysis Generated
May 18, 2026 - 13:30 vuln.today

DescriptionCVE.org

A flaw was found in gnutls. A remote attacker could exploit an issue in the Datagram Transport Layer Security (DTLS) packet reordering logic. The comparator function, responsible for ordering DTLS packets by sequence numbers, did not correctly handle packets with duplicate sequence numbers. This could lead to unstable packet ordering or undefined behavior, resulting in a denial of service.

AnalysisAI

Denial of service in GnuTLS affects the Datagram Transport Layer Security (DTLS) packet reordering logic, where the comparator function fails to correctly handle packets with duplicate sequence numbers. Remote unauthenticated attackers can send specially crafted DTLS packet sequences to trigger unstable ordering or undefined behavior, causing service disruption. No public exploit identified at time of analysis, and the issue is rated CVSS 7.5 (High) for availability impact only.

Technical ContextAI

GnuTLS is a widely deployed open-source implementation of the TLS and DTLS protocols, used as a TLS library by GNOME applications, CUPS, Wireshark, FFmpeg, and many Linux distributions as an alternative to OpenSSL. The flaw resides in DTLS-specific code that reorders out-of-order datagrams before passing them to the application layer - DTLS, unlike TLS, runs over UDP and must tolerate reordering and loss. CWE-475 (Undefined Behavior for Input to API) applies because the comparator function passed to the sorting routine violates strict weak ordering when two records share the same sequence number, which is undefined behavior in C library sort implementations (qsort/mergesort) and can yield inconsistent state, infinite loops, or memory corruption depending on the implementation.

RemediationAI

No vendor-released patch identified at time of analysis from the supplied references - monitor https://access.redhat.com/security/cve/CVE-2026-42009 and https://bugzilla.redhat.com/show_bug.cgi?id=2467279 for the fixed GnuTLS package versions and apply distribution updates (dnf/yum/apt) once published. As compensating controls until a patched build is available, restrict DTLS endpoints to trusted network segments via firewall rules on the UDP port in use (typically 443, 4433, or application-specific), rate-limit inbound DTLS handshakes and records at the network edge to blunt high-volume DoS attempts, and where feasible disable DTLS in favor of TLS-over-TCP for the affected service (trade-off: loses DTLS latency benefits and breaks UDP-based VPN/voice workloads). Switching the application's TLS backend to OpenSSL or another library is a heavier mitigation that may not be viable for distribution-packaged software.

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Same weakness CWE-475 – Undefined Behavior for Input to API

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Same technique Denial Of Service

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Vendor StatusVendor

SUSE

Severity: High
Product Status
openSUSE Tumbleweed Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Affected
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Affected

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CVE-2026-42009 vulnerability details – vuln.today
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