6.9

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2026-40476

CVE-2026-40476: graphql-php: Denial of Service via quadratic complexity in OverlappingFieldsCanBeMerged validation

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.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2026-40476

CVE-2026-40476:

6.9

CVSS Score

4.0

-

CVSS Score

Basic Information

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Technical Details

SSVC / BOD 26-04 ↗

Exploitation NoneAutomatable YesTech Impact Partial

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Package Name	Ecosystem	Vulnerable Versions	First Patched Version
webonyx/graphql-php	composer	<= 15.31.4	15.31.5

Technical Details

Vulnerability Intelligence
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Root Cause Analysis

The vulnerability lies in the OverlappingFieldsCanBeMerged validation rule, specifically within the collectConflictsWithin method. The vulnerability description explicitly mentions that this function performs O(n²) pairwise comparisons. By analyzing the patch commits between the vulnerable version (v15.31.4) and the patched version (v15.31.5), I identified commit b5e7c995b6e8b2c49149d1492a0a997da626491c. This commit modifies src/Validator/Rules/OverlappingFieldsCanBeMerged.php by introducing a deduplicateFields method and calling it at the beginning of collectConflictsWithin. This directly confirms that collectConflictsWithin was the location of the quadratic complexity issue. Before the patch, the function would perform a nested loop over all fields, and the fix was to reduce the number of items to be iterated over by deduplicating them first. Therefore, GraphQL\Validator\Rules\OverlappingFieldsCanBeMerged::collectConflictsWithin is the vulnerable function that would appear in a runtime profile during exploitation.

Vulnerable functions

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WAF Protection Rules

WAF Rule

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Reasoning

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