Improper Certificate ValidationWeakness · CWE-295

CVE-2026-42012

HIGH · 7.1 CVSS v3.1 Published 2026-05-26

Mitigation only

No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.

See remediation →

78/100

Remediation priority · High

Remotely reachable No privileges

Official description

NVD · unedited

A flaw was found in gnutls. A remote attacker could exploit this vulnerability by presenting a specially crafted certificate that contains Uniform Resource Identifier (URI) or Service (SRV) Subject Alternative Names (SANs). This could cause the certificate validation process to incorrectly fall back to checking DNS hostnames against the Common Name (CN), potentially allowing the attacker to spoof legitimate services or intercept sensitive information.

Technical summary

dbcve analysis · moderate confidence

A vulnerability in GnuTLS allows remote attackers to exploit certificate validation by presenting specially crafted certificates containing URI or SRV Subject Alternative Names. The flaw causes the validation process to incorrectly fall back to checking DNS hostnames against the Common Name (CN) field instead of properly validating the SANs, enabling potential spoofing and man-in-the-middle attacks.

MitigationUpdate GnuTLS to the latest patched version. For systems that cannot immediately update, implement certificate pinning or additional validation controls to ensure certificates are properly checked against their declared Subject Alternative Names before trusting the connection.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown

From the vector

Attack vector: Network
Complexity: Low
Privileges: None
User interaction: Required
Scope: Unchanged
Confidentiality: Low
Integrity: High
Availability: None

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

Am I affected?

dbcve checks

Work through these to decide whether this CVE applies to you.

Identify GnuTLS installation

Check for GnuTLS libraries on the system. On Linux, run 'ldconfig -p | grep gnutls' or look for libgnutls files in /usr/lib/. On systems with pkg-config, run 'pkg-config --modversion gnutls'.

Affected if GnuTLS libraries are found on the system
Determine installed GnuTLS version

Run 'gnutls-cli --version' or 'gnutls-serv --version' if available. Alternatively, check the library file version with 'rpm -q gnutls' (RHEL) or 'dpkg -l libgnutls*' (Debian).

Affected if The installed version falls within an affected but unpatched range (compare your version against any GnuTLS security advisories for this CVE)
Identify applications using GnuTLS for TLS

Review running services and applications that perform TLS/SSL certificate validation. Check configuration files for applications that specify GnuTLS as their TLS backend (common in web servers, mail servers, and VPN daemons).

Affected if Critical services rely on GnuTLS for certificate validation and are accessible over network
Verify SAN validation is in use

Examine certificate configurations for services using GnuTLS. Look for certificates containing URI or SRV Subject Alternative Names (SANs) by running 'openssl x509 -in <cert.pem> -noout -text' and checking the SAN extension field.

Affected if Services present certificates with URI or SRV SANs to clients, and those clients use GnuTLS for validation

You are likely affected if GnuTLS is installed, you use an unpatched version, and your environment relies on GnuTLS to validate certificates containing URI or SRV Subject Alternative Names.

Generated from the published advisory. Verify against your own configuration.

Remediation

From vendor data

Mitigation available No clean upgrade yet — mitigate in the meantime

Mitigation

Update GnuTLS to the latest patched version. For systems that cannot immediately update, implement certificate pinning or additional validation controls to ensure certificates are properly checked against their declared Subject Alternative Names before trusting the connection.

Have this fixed Scoped from the published advisory

Consultation2.0 h
Implementation8.0 h
Testing4.0 h
Review / QA2.0 h

16.0 hours of engineering $2,800

Get help mitigating

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,480.

Scan for this in your stack

Free · runs locally

dbcve dependency scanner

Check whether your project pulls in CVE-2026-42012 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-42012 in production — separate from our analysis above.

Notes0 Guidelines

Know something about CVE-2026-42012?

The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.

The version that genuinely resolved it — not the one the vendor claimed
A config change or rule that shut the vector down
A gotcha in the upgrade path that cost you an afternoon

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here

Verified mitigations, workarounds, and config changes
Version or environment caveats, and links to real fixes
No weaponised exploit code, or anything meant to cause harm
No spam, self-promotion, credentials, or personal data

At a glance

A fix existsA vendor remedy is published

Severity 7.1 High

Exploit likelihood EPSS, next 30 days 0.4%

Remediation

A high-priority fix

Have this fixed 16 hrs · Moderate

Typical engagement from $2,800

Get a fix See the full breakdown ↓

A high-priority vulnerability. Send your environment and a specialist will scope CVE-2026-42012 and return a fixed quote and timeline.

You’ll deal with our team directly and deploy the reviewed fix to staging first — never straight to production.

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

Check your environment

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

Scan for this in your stack

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Practitioner notes

No notes yet

Official description

Technical summary

CVSS breakdown

Am I affected?

Remediation

References