Bug 2450587 (CVE-2026-33308)

Summary:	CVE-2026-33308 mod_gnutls: apache httpd: mod_gnutls: Improper access to resources via client certificate key purpose bypass
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	Keywords:	Security
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Hardware:	All
OS:	Linux
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Doc Text:	A flaw was found in mod_gnutls, a TLS module for Apache HTTPD. Prior to version 0.13.0, the module's client certificate verification process did not properly validate the key purpose specified in the Extended Key Usage (EKU) extension. This oversight could allow a remote attacker, possessing a valid client certificate issued by a trusted Certificate Authority (CA) but intended for a different use, to improperly access resources that require TLS client authentication. This vulnerability enables unauthorized access to protected resources.	Story Points:	---
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2450683, 2450684
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Description OSIDB Bzimport 2026-03-24 03:02:04 UTC

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.