Craft CMS: Cloud Metadata SSRF Protection Bypass via IPv6 Resolution

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.5 · CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N/E:P · score source

EPSS

• CVE-2026-27129: 0.46% estimated exploitation activity in the next 30 days; percentile 40.26 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

The SSRF validation in Craft CMS’s GraphQL Asset mutation uses gethostbyname(), which only resolves IPv4 addresses. When a hostname has only AAAA (IPv6) records, the function returns the hostname string itself, causing the blocklist comparison to always fail and completely bypassing SSRF protection. This is a bypass of the security fix for CVE-2025-68437 (GHSA-x27p-wfqw-hfcc). Required Permissions Exploitation requires GraphQL schema permissions for: - Edit assets in the <VolumeName volume - Create assets in the <VolumeName volume These permissions may be granted to: - Authenticated users with appropriate GraphQL schema access - Public Schema (if misconfigured with write permissions) --- Technical Details Root Cause From PHP documentation: "gethostbyname - Get the IPv4 address corresponding to a given Internet host name" When no IPv4 (A record) exists, gethostbyname() returns the hostname string unchanged. Bypass Mechanism --- Bypass Payloads Blocked IPv4 Addresses and Their IPv6…

Published by the source

24 Feb 2026, 15:51 UTC

Last modified by the source

24 Feb 2026, 15:51 UTC

Source last checked

26 Oct 2026, 14:38 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-v2gc-rm6g-wrw9

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# Patch Next advisory brief: CVE-2026-27129

Advisory: Craft CMS: Cloud Metadata SSRF Protection Bypass via IPv6 Resolution
IDs: CVE-2026-27129, GHSA-v2gc-rm6g-wrw9
Record: https://patchnext.com/advisories/cve-2026-27129 (revision 1, source checked 26 Oct 2026, 14:38 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: craftcms/cms 5.8.23, 4.16.19. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist craftcms/cms: affected >= 5.0.0-RC1, <= 5.8.22; >= 3.5.0, <= 4.16.18; fixed in 5.8.23, 4.16.19

## Suggested inspection (read-only)
- Packagist craftcms/cms: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on craftcms/cms.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-v2gc-rm6g-wrw9 (GitHub-reviewed advisory GHSA-v2gc-rm6g-wrw9 lists affected ranges: Packagist craftcms/cms >=5.0.0-RC1 =3.5.0 <=4.16.18)

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