CVE-2026-42013 | Gnutls: gnutls: certificate validation bypass due to oversized subject alternative name

A flaw was found in gnutls. When validating certificates, an oversized Subject Alternative Name (SAN) could cause the validation process to incorrectly fall back to checking the Common Name (CN) field. This could allow a remote attacker to bypass proper certificate validation, potentially leading to spoofing or man-in-the-middle attacks.

Published: 2026-05-26 Last update: 2026-06-02 Assigner: [email protected] Source: [email protected]
NVD Status：Awaiting Analysis，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-42013 is rated Low Risk (38.6/100): CVSS High severity, with low exploitation likelihood (EPSS 0.05%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-42013

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-03 0.03% 0.05% +0.02%
2 2026-05-27 — 0.03% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-42013

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
8.2 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 4.2 [email protected]

Weakness enumeration for CVE-2026-42013

GitHub Security Advisory for CVE-2026-42013

GHSA-2pw7-g86g-76q7 · Severity: high — A flaw was found in gnutls. When validating certificates, an oversized Subject Alternative Name ...

OS Trackers for CVE-2026-42013

vendor priority summary link
debian not yet assigned CVE-2026-42013 not yet assigned priority: Debian including 1 source packages (gnutls28), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2026-42013
suse medium — https://www.suse.com/security/cve/CVE-2026-42013/
ubuntu medium CVE-2026-42013 medium priority: Ubuntu including 1 source packages (gnutls28), 8 status rows across 8 suites (bionic, focal, jammy, noble, questing, resolute, upstream, xenial): released 5, needs-triage 3. https://ubuntu.com/security/CVE-2026-42013

Affected software / configurations for CVE-2026-42013

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2026-42013

cvelogic Threat Intelligence