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CVE Record

CVE-2026-42009: Gnutls: gnutls: denial of service via dtls packet reordering vulnerability

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.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-42009 is a remotely reachable denial-of-service flaw in GnuTLS DTLS packet handling. An unauthenticated attacker may be able to disrupt affected services by triggering unstable packet ordering. The impact is availability only, but the affected Red Hat footprint is broad across RHEL 7 ELS, 8, 9, and 10 streams.

Executive priority

Treat as a high-priority availability risk, not a data-theft issue. Patch affected Red Hat systems on normal emergency or accelerated maintenance timelines, starting with externally reachable DTLS-dependent services and systems supporting critical business processes.

Technical view

The flaw is in GnuTLS DTLS packet reordering logic. A comparator used to order DTLS packets by sequence number mishandles duplicate sequence numbers, causing unstable ordering or undefined behavior and possible denial of service. CVSS 3.1 is 7.5, AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Likely exposure

Exposure is most likely on Red Hat systems running affected gnutls packages, especially where applications use DTLS over reachable network paths. The bundle lists affected RHEL 10, 10.0 EUS, 9, 9.4 SAP, 8, 8.4, 8.6, 8.8 SAP/TUS, and 7 ELS package streams.

Exploitation context

The source bundle does not show CISA KEV listing or confirmed active exploitation. The vulnerability is still operationally important because it is network reachable, requires no authentication or user interaction, and targets availability of services using affected DTLS handling.

Researcher notes

The provided evidence identifies duplicate DTLS sequence numbers as the logic edge case and CWE-475 as the weakness. It does not provide proof-of-concept details, exploit telemetry, or fixed version mapping beyond Red Hat advisory references, so validation should stay package- and service-inventory focused.

Mitigation direction

  • Apply the relevant Red Hat security advisory updates for affected systems.
  • Check Red Hat guidance for exact fixed package versions in each supported stream.
  • Prioritize internet-facing or partner-facing services that use DTLS via GnuTLS.
  • Reduce untrusted DTLS exposure where patching cannot happen immediately.
  • Monitor affected services for crashes, restarts, or availability degradation.

Validation and detection

  • Inventory installed gnutls and listed libtasn1 package versions on Red Hat hosts.
  • Map applications linked to GnuTLS and confirm whether they use DTLS.
  • Verify the applicable RHSA has been installed for each RHEL stream.
  • Confirm exposed DTLS services are patched or temporarily access-restricted.
  • Review service logs and monitoring for denial-of-service symptoms.
Prepared
Confidence
high
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-475: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
description · low confidence lookup

Container behavior lookup

The affected technology mentions containers, so container-specific ATT&CK technique review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-42009 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
7Timeline events
2ADP providers
24Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-42009Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. Source timelineredhat

    Made public.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. Source timelineredhat

    Reported to Red Hat.

  6. CVE publishedCVE Program

    The CVE record was published.

  7. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPgnutls: gnutls: Denial of Service via DTLS packet reordering vulnerability
other:Red Hat severity ratingcvssV3_1
  • 2026-05-06T16:32:32.382Z: Reported to Red Hat.
  • 2026-04-29T00:00:00.000Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Red HatRed Hat Enterprise Linux 10gnutls, 0:3.8.10-4.el10_2affected
Red HatRed Hat Enterprise Linux 10.0 Extended Update Supportgnutls, 0:3.8.9-9.el10_0.19affected
Red HatRed Hat Enterprise Linux 7 Extended Lifecycle Supportgnutls, 0:3.3.29-9.el7_9.1affected
Red HatRed Hat Enterprise Linux 8gnutls, 0:3.6.16-8.el8_10.6affected
Red HatRed Hat Enterprise Linux 8gnutls, 0:3.6.16-8.el8_10.6affected
Red HatRed Hat Enterprise Linux 8.4 Advanced Mission Critical Update Supportgnutls, 0:3.6.14-10.el8_4.1affected
Red HatRed Hat Enterprise Linux 8.4 Advanced Mission Critical Update Supportlibtasn1, 0:4.13-3.el8_4.1affected
Red HatRed Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-Ongnutls, 0:3.6.14-10.el8_4.1affected
Red HatRed Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-Onlibtasn1, 0:4.13-3.el8_4.1affected
Red HatRed Hat Enterprise Linux 8.6 Advanced Mission Critical Update Supportgnutls, 0:3.6.16-5.el8_6.5affected
Red HatRed Hat Enterprise Linux 8.6 Advanced Mission Critical Update Supportlibtasn1, 0:4.13-3.el8_6.2affected
Red HatRed Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-Ongnutls, 0:3.6.16-5.el8_6.5affected
Red HatRed Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-Onlibtasn1, 0:4.13-3.el8_6.2affected
Red HatRed Hat Enterprise Linux 8.8 Telecommunications Update Servicegnutls, 0:3.6.16-7.el8_8.4affected
Red HatRed Hat Enterprise Linux 8.8 Telecommunications Update Servicelibtasn1, 0:4.13-4.el8_8.1affected
Red HatRed Hat Enterprise Linux 8.8 Update Services for SAP Solutionsgnutls, 0:3.6.16-7.el8_8.4affected
Red HatRed Hat Enterprise Linux 8.8 Update Services for SAP Solutionslibtasn1, 0:4.13-4.el8_8.1affected
Red HatRed Hat Enterprise Linux 9gnutls, 0:3.8.10-4.el9_8affected
Red HatRed Hat Enterprise Linux 9gnutls, 0:3.8.10-4.el9_8affected
Red HatRed Hat Enterprise Linux 9.4 Update Services for SAP Solutionsgnutls, 0:3.8.3-4.el9_4.6affected
Red HatRed Hat Enterprise Linux 9.6 Extended Update Supportgnutls, 0:3.8.3-6.el9_6.4affected
Red HatRed Hat OpenShift Container Platform 4.20rhcos, 4.20.9.6.202607010620-0affected
Red HatRed Hat OpenShift Container Platform 4.21rhcos, 4.21.9.6.202607011303-0affected
Red HatRed Hat OpenShift Container Platform 4.22rhcos, 4.22.9.8.202606230855-0affected
Red HatRed Hat AI Inference Server 3.2rhaiis/model-opt-cuda-rhel9, 1782951051affected
Red HatRed Hat AI Inference Server 3.2rhaiis/vllm-cuda-rhel9, 1782951012affected
Red HatRed Hat AI Inference Server 3.2rhaiis/vllm-rocm-rhel9, 1782951244affected
Red HatRed Hat Discovery 2discovery/discovery-server-rhel9, 1782159791affected
Red HatRed Hat Discovery 2discovery/discovery-ui-rhel9, 1782166952affected
Red HatRed Hat Hardened Imagesgnutls-main, 3.8.13-1.hum1affected
Weakness

CWE details

CWE-475

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.