graphql-php is affected by a Denial of Service via quadratic complexity in OverlappingFieldsCanBeMerged validation

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-40476: 0.64% estimated exploitation activity in the next 30 days; percentile 50.59 (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 OverlappingFieldsCanBeMerged validation rule exhibits quadratic time complexity when processing queries with many repeated fields sharing the same response name. An attacker can send a crafted query like { hello hello hello ... } with thousands of repeated fields, causing excessive CPU usage during validation before execution begins. This is not mitigated by existing QueryDepth or QueryComplexity rules. Observed impact (tested on v15.31.4): - 1000 fields: ~0.6s - 2000 fields: ~2.4s - 3000 fields: ~5.3s - 5000 fields: request timeout (20s) Root cause: collectConflictsWithin() performs O(n²) pairwise comparisons of all fields with the same response name. For identical repeated fields, every comparison returns "no conflict" but the quadratic iteration count causes resource exhaustion. Fix: Deduplicate structurally identical fields before pairwise comparison, reducing the complexity from O(n²) to O(u²) where u is the number of unique field signatures (typically 1 for this attack…

Published by the source

14 Apr 2026, 01:05 UTC

Last modified by the source

8 Jun 2026, 23:09 UTC

Source last checked

26 Oct 2026, 14:48 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-68jq-c3rv-pcrr

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# Patch Next advisory brief: CVE-2026-40476

Advisory: graphql-php is affected by a Denial of Service via quadratic complexity in OverlappingFieldsCanBeMerged validation
IDs: CVE-2026-40476, GHSA-68jq-c3rv-pcrr
Record: https://patchnext.com/advisories/cve-2026-40476 (revision 1, source checked 26 Oct 2026, 14:48 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: webonyx/graphql-php 15.31.5. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist webonyx/graphql-php: affected <= 15.31.4; fixed in 15.31.5

## Suggested inspection (read-only)
- Packagist webonyx/graphql-php: 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 webonyx/graphql-php.
- 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-68jq-c3rv-pcrr (GitHub-reviewed advisory GHSA-68jq-c3rv-pcrr lists affected ranges: Packagist webonyx/graphql-php >=0 <=15.31.4)

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