IPv6 ACL bypass in FastCGI listen.allowed_clients due to partial address comparison (memcmp 12 bytes)
At a glance
Severity
MEDIUM 6.5
EPSS
EPSS 0.38 % · percentile 31 (2026-10-27)
State
PUBLISHED
Published
Updated
Assigner
php
NVD status
Analyzed
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.
