CVE-2026-42013: gnutls28 Improper Certificate Validation
Vulnerability summary
CVE-2026-42013 is a high (CVSS 8.2) Improper Certificate Validation vulnerability in gnutls28. EPSS estimates a 0.56% chance of exploitation in the next 30 days, higher than 45.7% of scored vulnerabilities.
Advisory lineage
Upstream 0 · Downstream 17 · Related 6Timeline
- 26-05-2026PublishedVulnerability first disclosed.
- 14-10-2026Last modifiedVulnerability information updated.
Description
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.
CVSS metrics
5 scores · 5 sources · 1 version- OSV · AlpineEcosystem advisory · calculated8.2HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N
- OSV · UbuntuEcosystem advisory · calculated8.2HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N
- OSV · DebianEcosystem advisory · calculated8.2HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N
- NVDNIST8.2HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N
EPSS trend
Probability
0.56%
Chance of exploitation in the next 30 days
Percentile
46%
Versus all other CVEs
30-day change
+0.14 pp
From 0.42% on 19-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Alpine1 product
- gnutls< 3.8.13-r0
Debian1 product
- gnutls28< 3.7.9-2+deb12u7 | < 3.8.9-3+deb13u4 | < 3.8.13-1
Ubuntu1 product
- gnutls28< 3.4.10-4ubuntu1.9+esm4 | < 3.5.18-1ubuntu1.6+esm4 | < 3.6.13-2ubuntu1.12+esm3 | < 3.7.3-4ubuntu1.9 | All versions (No fix recorded) | < 3.7.3-4ubuntu1.9+Fips1 | < 3.8.3-1.1ubuntu3.6 | < 3.8.3-1.1ubuntu3.6+Fips1.2 | < 3.8.9-3ubuntu2.2 | < 3.8.12-2ubuntu1.1
3 vendors · 3 products
