What’s Vulnerable › Vulnerabilities
CVE-2026-91768: IPv6 ACL bypass in FastCGI listen.allowed_clients due to partial address comparison (memcmp 12 bytes)
- Severity: medium (CVSS 6.5 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.4% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-09-25 · updated 2026-10-27
- Weakness: CWE-1023
Description
The IPv6 branch of the FastCGI client access check compares only the first 12 bytes of a 16-byte IPv6 address, so listen.allowed_clients matches on a /96 prefix instead of the exact address. An attacker who can source an address sharing the first 96 bits with an allowed one passes the check and reaches the FastCGI endpoint.
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
- PHP: from 8.2.* before 8.2.34; from 8.3.* before 8.3.35; from 8.4.* before 8.4.26; from 8.5.* 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; PHP 8.2.34, 8.3.35, 8.4.26, 8.5.11. Check the vendor advisory for mitigations.
References
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