Bug 2542493 (CVE-2026-91769)

Summary: CVE-2026-91769 php: php: Server impersonation via Common Name fallback in TLS verification
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in PHP. This vulnerability allows server impersonation and potential information disclosure during Transport Layer Security (TLS) connections. When verifying peer certificates, PHP improperly falls back to matching the Common Name (CN) if no Subject Alternative Name (SAN) matches the requested hostname. An attacker could exploit this flaw by presenting a certificate trusted for another domain whose CN matches the target, enabling them to impersonate a legitimate server and intercept sensitive data.
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Bug Depends On: 2543804    
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Description OSIDB Bzimport 2026-09-28 13:53:06 UTC 
PHP's OpenSSL stream peer verification checks the certificate's subjectAltName entries first and, whenever no entry matches, falls back to the Common Name. RFC 6125 requires the CN to be ignored once the certificate presents any service identity, so a certificate carrying a non-matching DNS SAN was still accepted when its CN matched the requested peer_name. A certificate trusted by the client for one name can therefore be used to impersonate another.
Comment 1 Jon Orris 2026-10-21 15:45:15 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2026:87080 https://access.redhat.com/errata/RHSA-2026:87080