What’s Vulnerable › Vulnerabilities
CVE-2026-91769: TLS Hostname Verification Falls Back to CN After SAN Mismatch
- Severity: medium (CVSS 4.3 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2026-09-25 · updated 2026-10-23
- Weakness: CWE-297
Description
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.
Affected products
- PHP: from 8.2.0 before 8.2.34; from 8.3.0 before 8.3.35; from 8.4.0 before 8.4.26; from 8.5.0 before 8.5.11 — fixed in 8.2.34, 8.3.35, 8.4.26, 8.5.11
How to fix
Upgrade to a fixed version: PHP 8.2.34, 8.3.35, 8.4.26, 8.5.11. Check the vendor advisory for mitigations.
References
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