GHSA-68jq-c3rv-pcrr

The `OverlappingFieldsCanBeMerged` validation rule exhibits quadratic time complexity when processing queries with many repeated fields sharing the same response name. An attacker can send a crafted query like `{ hello hello hello ... }` with thousands of repeated fields, causing excessive CPU usage during validation before execution begins.

This is not mitigated by existing QueryDepth or QueryComplexity rules.

**Observed impact (tested on v15.31.4):** - 1000 fields: ~0.6s - 2000 fields: ~2.4s - 3000 fields: ~5.3s - 5000 fields: request timeout (>20s)

**Root cause:** `collectConflictsWithin()` performs O(n²) pairwise comparisons of all fields with the same response name. For identical repeated fields, every comparison returns "no conflict" but the quadratic iteration count causes resource exhaustion.

**Fix:** Deduplicate structurally identical fields before pairwise comparison, reducing the complexity from O(n²) to O(u²) where u is the number of unique field signatures (typically 1 for this attack pattern).

**Credit:** Ashwak N (ashwakn04@gmail.com)