GHSA-fc86-6rv6-2jpm

Summary

OverlappingFieldsCanBeMerged validation rule has O(n^2 x m^2) worst case via flattened inline fragments. The CVE-2023-26144 named-fragment cache does not cover inline fragments. A 364 KB query (200 outer x 100 inner inline fragments) consumes 117 seconds of CPU per request, with no comparison budget and no validation timeout.

Affected Component

src/Validator/Rules/OverlappingFieldsCanBeMerged.php

Description

graphql-php is a PHP port of graphql-js and inherits the same OverlappingFieldsCanBeMerged algorithm. The rule performs an explicit O(n^2) pairwise comparison loop over fields collected for each response name (collectConflictsWithin), and recurses into sub-selections via findConflict. When the rule receives a query in which several inline fragments select the same response name at multiple nesting levels, the cost compounds to O(n^2 x m^2) where n and m are the number of inline fragments at the outer and inner levels respectively.

graphql-php includes a comparedFragmentPairs PairSet cache (the same class of memoization fix tracked under CVE-2023-26144 / GHSA-9pv7-vfvm-6vr7), but it is keyed by named fragment identity. Inline fragments have no name; they are flattened into the parent $astAndDefs map by the case $selection instanceof InlineFragmentNode branch starting at OverlappingFieldsCanBeMerged.php:266, so they are never observed by the cache. Every pair must be re-compared from scratch on every nesting level.

This finding has been tested against the latest stable release webonyx/graphql-php@v15.31.4 running on PHP 8.3.30.

Root Cause

1. Pairwise O(n^2) loop (collectConflictsWithin)

// src/Validator/Rules/OverlappingFieldsCanBeMerged.php:306
$fieldsLength = count($fields);

if ($fieldsLength > 1) {
    for ($i = 0; $i < $fieldsLength; ++$i) {                             // line 311
        for ($j = $i + 1; $j <...