PHP OpenSSL Peer Verif: CN Fallback Enables Privilege Impersonation
CVE-2026-91769 Published on September 25, 2026

TLS Hostname Verification Falls Back to CN After SAN Mismatch
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.

Vendor Advisory NVD

Vulnerability Analysis

Attack Vector:
ADJACENT_NETWORK
Attack Complexity:
LOW
Privileges Required:
NONE
User Interaction:
NONE
Scope:
UNCHANGED
Confidentiality Impact:
LOW
Integrity Impact:
NONE
Availability Impact:
NONE

Weakness Type

Improper Validation of Certificate with Host Mismatch

The software communicates with a host that provides a certificate, but the software does not properly ensure that the certificate is actually associated with that host.


Products Associated with CVE-2026-91769

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PHP
 
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Affected Versions

PHP Group PHP: