CVE-2026-33308
CVE-2026-33308 is a medium-severity vulnerability in Mod Gnutls Project Mod Gnutls with a CVSS 3.x base score of 6.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-295.
Key facts
- Severity: Medium (CVSS 3.x base score 6.8)
- EPSS exploit prediction: 0% (11th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-14694
- Weakness: CWE-295
- Affected product: Mod Gnutls Project Mod Gnutls
- Published:
- Last modified:
Description
Mod_gnutls is a TLS module for Apache HTTPD based on GnuTLS. Prior to version 0.13.0, code for client certificate verification did not check the key purpose as set in the Extended Key Usage extension. An attacker with access to the private key for a valid certificate issued by a CA trusted for TLS client authentication but designated for a different purpose could have used that certificate to improperly access resources requiring TLS client authentication. Server configurations that do not use client certificates (`GnuTLSClientVerify ignore`, the default) are not affected. The problem has been fixed in version 0.13.0 by rewriting certificate verification to use `gnutls_certificate_verify_peers()`, and requiring key purpose id-kp-clientAuth (also known as `tls_www_client` in GnuTLS) by default if the Extended Key Usage extension is present. The new `GnuTLSClientKeyPurpose` option allows overriding the expected key purpose if needed (please see the manual for details). Behavior for certificates without an Extended Key Usage extension is unchanged. If dedicated (sub-)CAs are used for issuing TLS client certificates only (not for any other purposes) the issue has no practical impact.
Frequently asked questions
- What is CVE-2026-33308?
- Mod_gnutls is a TLS module for Apache HTTPD based on GnuTLS. Prior to version 0.13.0, code for client certificate verification did not check the key purpose as set in the Extended Key Usage extension. An attacker with access to the private key for a valid certificate issued by a CA trusted for TLS client authentication but designated for a different purpose could have used that certificate to improperly access resources requiring TLS client authentication. Server configurations that do not use client certificates (`GnuTLSClientVerify ignore`, the default) are not affected. The problem has been fixed in version 0.13.0 by rewriting certificate verification to use `gnutls_certificate_verify_peers()`, and requiring key purpose id-kp-clientAuth (also known as `tls_www_client` in GnuTLS) by default if the Extended Key Usage extension is present. The new `GnuTLSClientKeyPurpose` option allows overriding the expected key purpose if needed (please see the manual for details). Behavior for certificates without an Extended Key Usage extension is unchanged. If dedicated (sub-)CAs are used for issuing TLS client certificates only (not for any other purposes) the issue has no practical impact.
- How severe is CVE-2026-33308?
- CVE-2026-33308 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity none, and availability none.
- Is CVE-2026-33308 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (11th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-33308?
- CVE-2026-33308 affects Mod Gnutls Project Mod Gnutls. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-33308?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2026-33308 have an EU (EUVD) identifier?
- Yes. CVE-2026-33308 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-14694.
- When was CVE-2026-33308 published?
- CVE-2026-33308 was published on 2026-03-24 and last updated on 2026-06-17.
References
Affected products (1)
- cpe:2.3:a:mod_gnutls_project:mod_gnutls:*:*:*:*:*:*:*:*
More vulnerabilities in Mod Gnutls Project Mod Gnutls
- CVE-2026-33307 — High (CVSS 7.5): Mod_gnutls is a TLS module for Apache HTTPD based on GnuTLS. In versions prior to 0.12.3 and 0.13.0, code for client…
- CVE-2023-25824 — High (CVSS 7.5): Mod_gnutls is a TLS module for Apache HTTPD based on GnuTLS. Versions from 0.9.0 to 0.12.0 (including) did not properly…
- CVE-2009-5144 — High (CVSS 7.5): mod-gnutls does not validate client certificates when "GnuTLSClientVerify require" is set in a directory context, which…
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