CVE-2026-40476 graphql-php: Denial of Service via quadratic complexity in OverlappingFieldsCanBeMerged validation
An attacker can cause excessive CPU usage and denial of service by sending queries with many repeated fields to the graphql-php library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40476?
CVE-2026-40476 is a medium-severity denial of service vulnerability in webonyx graphql-php, published on 17 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
graphql-go is a Go implementation of GraphQL. In versions 15.31.4 and below, the OverlappingFieldsCanBeMerged validation rule performs O(n²) pairwise comparisons of fields sharing the same response name. An attacker can send a query with thousands of repeated identical fields, causing excessive CPU usage during validation before execution begins. This is not mitigated by existing QueryDepth or QueryComplexity rules. This issue has been fixed in version 15.31.5.
Weakness: CWE-407
Which versions are affected by CVE-2026-40476?
2 open source packages ship an affected version, including webonyx/graphql-php. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
webonyx/graphql-php Packagist | All versions | 15.31.5 |
webonyx/graphql-php Packagist | All versions | 15.31.5 |
Products include Webonyx Graphql-Php.
How do I fix CVE-2026-40476?
Upgrade webonyx/graphql-php to 15.31.5 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-40476 being exploited?
There is no known exploitation of CVE-2026-40476 in the wild and no public exploit code.
Sources
Also known as GHSA-68jq-c3rv-pcrr.