{"id":"GHSA-fc86-6rv6-2jpm","aliases":[],"url":"https://o3.security/vulnerability/GHSA-fc86-6rv6-2jpm","summary":"webonyx/graphql-php has quadratic validation cost in OverlappingFieldsCanBeMerged via inline fragments","details":"## Summary\n\n`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.\n\n## Affected Component\n\n`src/Validator/Rules/OverlappingFieldsCanBeMerged.php`\n\n## Description\n\ngraphql-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.\n\ngraphql-php includes a `comparedFragmentPairs` PairSet cache (the same class of memoization fix tracked under [CVE-2023-26144 / GHSA-9pv7-vfvm-6vr7](https://github.com/advisories/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 $selection instanceof InlineFragmentNode` branch starting at `OverlappingFieldsCanBeMerged.php:266`, so they are never observed by the cache. Every pair must be re-compared from scratch on every nesting level.\n\nThis finding has been tested against the **latest stable release `webonyx/graphql-php@v15.31.4`** running on PHP 8.3.30.\n\n## Root Cause\n\n### 1. Pairwise `O(n^2)` loop (`collectConflictsWithin`)\n\n```php\n// src/Validator/Rules/OverlappingFieldsCanBeMerged.php:306\n$fieldsLength = count($fields);\n\nif ($fieldsLength > 1) {\n for ($i = 0; $i < $fieldsLength; ++$i) { // line 311\n for ($j = $i + 1; $j < $fieldsLength; ++$j) { // line 312\n $conflict = $this->findConflict(\n $context,\n $parentFieldsAreMutuallyExclusive,\n $responseName,\n $fields[$i],\n $fields[$j]\n );\n // ...\n }\n }\n}\n```\n\n`count($fields)` grows without bound when multiple inline fragments select the same response name in the same parent selection set.\n\n### 2. Inline fragment flattening (`internalCollectFieldsAndFragmentNames`)\n\n```php\n// src/Validator/Rules/OverlappingFieldsCanBeMerged.php:266\ncase $selection instanceof InlineFragmentNode:\n $typeCondition = $selection->typeCondition;\n $inlineFragmentType = $typeCondition === null\n ? $parentType\n : AST::typeFromAST([$context->getSchema(), 'getType'], $typeCondition);\n\n $this->internalCollectFieldsAndFragmentNames(\n $context,\n $inlineFragmentType,\n $selection->selectionSet,\n $astAndDefs, // flattened into the parent map\n $fragmentNames\n );\n break;\n```\n\n`N` inline fragments selecting the same response name produce `N` entries in `$astAndDefs[$responseName]`, which then trigger `N*(N-1)/2` `findConflict` calls.\n\n### 3. The named-fragment cache does not cover this code path\n\n```php\n// src/Validator/Rules/OverlappingFieldsCanBeMerged.php:41\nprotected PairSet $comparedFragmentPairs;\n\n// :54 (in __construct)\n$this->comparedFragmentPairs = new PairSet();\n```\n\n`PairSet` is keyed by `(fragmentName1, fragmentName2)`. Inline fragments have no name; they are folded into the parent selection set before the cache is even consulted. The CVE-2023-26144 fix has zero effect on this code path.\n\n### 4. No comparison budget, no validation timeout\n\nThere is no counter shared across `collectConflictsWithin`, `collectConflictsBetween`, and the recursive `findConflict` calls. The rule runs to completion regardless of cost. graphql-php exposes no `validate_timeout` equivalent.\n\n## Proof of Concept\n\n```php\n