---
id: CVE-2026-91768
title: >-
  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
summary: >-
  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 …
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N'
cwe:
  - CWE-1023
  - CWE-940
vendor: PHP Group
product: PHP-FPM
affected:
  - PHP-FPM >= 8.2.* < 8.2.34
  - PHP-FPM >= 8.3.* < 8.3.35
  - PHP-FPM >= 8.4.* < 8.4.26
  - PHP-FPM >= 8.5.* < 8.5.11
published: '2026-09-25'
updated: '2026-09-25'
sourceUpdated: '2026-09-25T22:18:49.807'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-91768'
references:
  - url: 'https://github.com/php/php-src/security/advisories/GHSA-62xp-839h-2637'
    label: security@php.net
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-91768.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-91768'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2541660'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-91768'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-91768'
  - url: 'https://access.redhat.com/errata/RHSA-2026:70720'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
ingestedAt: '2026-09-25T21:19:40.216Z'
patched:
  - hardened_images
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **RHSA-2026:70720** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-23 · [advisory](https://access.redhat.com/errata/RHSA-2026:70720)
- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, … · updated 2026-09-26 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-91768.json)