parse-server has GraphQL complexity validator exponential fragment traversal DoS

Impact

The GraphQL query complexity validator can be exploited to cause a denial-of-service by sending a crafted query with binary fan-out fragment spreads. A single unauthenticated request can block the Node.js event loop for seconds, denying service to all concurrent users. This only affects deployments that have enabled the requestComplexity.graphQLDepth or requestComplexity.graphQLFields configuration options.

Patches

The fix replaces the per-branch fragment traversal with memoized fragment computation, reducing the traversal from exponential O(2^N) to linear O(N) time. Additionally, early termination aborts the traversal as soon as configured limits are exceeded.

Workarounds

Disable GraphQL complexity limits by setting requestComplexity.graphQLDepth and requestComplexity.graphQLFields to -1 (the default).

Resources

• GitHub security advisory: https://github.com/parse-community/parse-server/security/advisories/GHSA-mfj6-6p54-m98c
• Fix Parse Server 9: https://github.com/parse-community/parse-server/pull/10344
• Fix Parse Server 8: https://github.com/parse-community/parse-server/pull/10345