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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-91768
StatePUBLISHED
Assignerphp
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-25 22:18:49 UTC
Updated2026-10-27 15:40:27 UTC
DescriptionThe 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.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from [email protected]

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS: 0.005610000 probability, percentile 0.444740000 (date 2026-09-29)

Problem Types: CWE-1023 | CWE-1023 CWE-1023

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.5MEDIUMCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
3.1CNACVSS6.5MEDIUMCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Adjacent
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Php Php All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA PHP Group PHP affected 8.2.* 8.2.34 semver Not specified
CNA PHP Group PHP affected 8.3.* 8.3.35 semver Not specified
CNA PHP Group PHP affected 8.4.* 8.4.26 semver Not specified
CNA PHP Group PHP affected 8.5.* 8.5.11 semver Not specified

References

ReferenceSourceLinkTags
github.com/php/php-src/security/advisories/GHSA-62xp-839h-2637 [email protected] github.com Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: @l8BL (GitHub) (en)

CNA: @OSTIF-Derek (GitHub) (en)

CNA: Ilia Alshanetsky (en)

CNA: Alexandre Daubois (en)

CNA: Arnaud Le Blanc (en)

CNA: Jakub Zelenka (en)

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