CVE-2026-40324

Impact

Hot Chocolate's Utf8GraphQLParser is a recursive descent parser with no recursion depth limit. A crafted GraphQL document with deeply nested selection sets, object values, list values, or list types can trigger a StackOverflowException on payloads as small as 40 KB.

Because StackOverflowException is uncatchable in .NET (since .NET 2.0), the entire worker process is terminated immediately. All in-flight HTTP requests, background IHostedService tasks, and open WebSocket subscriptions on that worker are dropped. The orchestrator (Kubernetes, IIS, etc.) must restart the process.

This occurs before any validation rules run — MaxExecutionDepth, complexity analyzers, persisted query allow-lists, and custom IDocumentValidatorRule implementations cannot intercept the crash because Utf8GraphQLParser.Parse is invoked before validation. The existing MaxAllowedFields=2048 limit does not help because the crashing payloads contain very few fields.

Severity: Critical (9.1) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Patches

• v12 line: Fixed in 12.22.7
• v13 line: Fixed in 13.9.16
• v14 line: Fixed in 14.3.1
• v15 line: Fixed in 15.1.14

The fix adds a MaxAllowedRecursionDepth option to ParserOptions with a safe default, and enforces it across all recursive parser methods (ParseSelectionSet, ParseValueLiteral, ParseObject, ParseList, ParseTypeReference, etc.). When the limit is exceeded, a catchable SyntaxException is thrown instead of overflowing the stack.

Workarounds

There is no application-level workaround. StackOverflowException cannot be caught in .NET. The only mitigation is to upgrade to a patched version.

Operators can reduce (but not eliminate) risk by limiting HTTP request body size at the reverse proxy or load balancer layer, though the smallest crashing payload (40 KB) is well below most default body size limits and is highly compressible (~few hundred bytes via gzip).

References

• Fix for v15: https://github.com/ChilliCream/graphql-platform/pull/9528