CVE-2026-91768 IPv6 ACL bypass in FastCGI listen.allowed_clients due to partial address comparison (memcmp 12 bytes)

What is CVE-2026-91768?

CVE-2026-91768 is a medium-severity authentication bypass vulnerability in Php Php, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official 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.

Weakness: CWE-1023

Which versions are affected by CVE-2026-91768?

3 open source packages ship an affected version, including libphp, php and php-min. It affects 1 product.

Products include Php Php.

How do I fix CVE-2026-91768?

Upgrade libphp to a fixed version for your release line: 8.2.34, 8.3.35, 8.4.26 or 8.5.11.

Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.

Is CVE-2026-91768 being exploited?

There is no known exploitation of CVE-2026-91768 in the wild and no public exploit code.

Other vulnerabilities in Php Php

• CVE-2012-2688 Integer overflow in n/a Critical 10.0
• CVE-2012-2376 Memory corruption in n/a Critical 10.0
• CVE-2011-3268 Memory corruption in n/a Critical 10.0
• CVE-2009-4143 Other in n/a Critical 10.0
• CVE-2008-5557 Memory corruption in n/a Critical 10.0

All Php Php vulnerabilities

Sources

• CVE record
• NVD
• OSV
• How this page is made

Also known as AZL-104895, BELL-CVE-2026-91768, BIT-libphp-2026-91768, BIT-php-2026-91768, BIT-php-min-2026-91768, CLEANSTART-2026-XM64150 and 11 more.