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CVE Record

CVE-2026-42010: Gnutls: gnutls: authentication bypass via nul character in username

A flaw was found in gnutls. Servers configured with RSA-PSK (Rivest–Shamir–Adleman – Pre-Shared Key) wrongfully matched usernames containing a NUL character with truncated usernames. A remote attacker could exploit this by sending a specially crafted username, leading to an authentication bypass. This vulnerability allows an attacker to gain unauthorized access by circumventing the authentication process.

HighCVSS 7.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This is an authentication bypass in GnuTLS when a server uses RSA-PSK authentication. A specially formed username containing a NUL character can be matched as a shorter username, potentially letting an attacker access protected services as another identity.

Executive priority

Treat as a high-priority patching item where GnuTLS RSA-PSK protects sensitive or externally reachable services. It is not currently documented as exploited in the provided sources, but authentication bypass against confidentiality-sensitive systems warrants prompt action.

Technical view

GnuTLS servers configured for RSA-PSK can compare usernames incorrectly when a NUL byte is present, causing truncation-style matching. The issue is tracked as CWE-170 and CWE-626, with CVSS 3.1 score 7.1. Red Hat lists affected gnutls packages across RHEL 8, 9, 10, and selected EUS/AUS/TUS/SAP streams.

Likely exposure

Exposure is most likely on Linux services using Red Hat-packaged GnuTLS with RSA-PSK authentication enabled. Systems with GnuTLS installed but not serving RSA-PSK authentication are less directly exposed based on the provided evidence.

Exploitation context

The bundle describes remote exploitation with low privileges and no user interaction. CISA KEV is false, and the supplied sources do not claim active exploitation or public exploit availability.

Researcher notes

Focus validation on actual RSA-PSK server configurations rather than GnuTLS presence alone. The affected list is Red Hat-centric and includes multiple lifecycle streams. Evidence does not establish impact for every upstream or downstream consumer beyond the supplied affected package data.

Mitigation direction

  • Apply the relevant Red Hat security advisory updates for each affected RHEL stream.
  • Prioritize internet-facing or sensitive services that use GnuTLS RSA-PSK authentication.
  • If updates are delayed, check vendor guidance for supported temporary mitigations.
  • Review non-Red Hat distributions against their own vendor advisories before assuming exposure or fixes.

Validation and detection

  • Inventory systems running affected RHEL streams and gnutls package versions.
  • Identify services configured to use GnuTLS RSA-PSK authentication.
  • Compare installed package versions against the affected versions and RHSA advisories.
  • Confirm remediation by verifying updated package versions after patching.
  • Review authentication logs for unusual failed or unexpected username patterns.
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-170: 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
cwe · low confidence lookup

CWE-626: 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

Credential and access behavior lookup

The CVE wording references authentication or credential exposure, so valid-account and credential-access review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program 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-2026-42010 mapping review

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

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.1 (3.1)
Known Exploited
No
Published

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

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
23Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical 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
7.1CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N2.84.2redhat
7.1CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N2.84.2redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.1High
CVSS 3.1 vector shape for CVE-2026-42010Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

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: Authentication Bypass via NUL Character in Username
other:Red Hat severity ratingcvssV3_1
  • 2026-05-06T16:57:37.044Z: 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 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, 4.22.9.8.202606301732-0affected
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
Red HatRed Hat Update Infrastructure 5rhui5/cds-rhel9, 1781525684affected
Weakness

CWE details

CWE-170CWE-626

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

CWE-170 · source CWE mapping

Improper Null Termination

Improper Null Termination represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-626 · source CWE mapping

Null Byte Interaction Error (Poison Null Byte)

Null Byte Interaction Error (Poison Null Byte) represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs