CVE-2026-40324 is a critical-severity (CVSS 9.1) CWE-674 vulnerability in HotChocolate.Language. A fix is available for HotChocolate.Language — see the affected versions and patch details below.
Hot Chocolate's Utf8GraphQLParser has Stack Overflow via Deeply Nested GraphQL Documents
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-40324.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-40324 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
HotChocolate.Language.NETHotChocolate.Language.NETHotChocolate.Language.NETHotChocolate.LanguageReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.
Description
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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | HotChocolate.Language | all versions | 12.22.7dotnet add package HotChocolate.Language --version 12.22.7 |
| .NETNuGet | HotChocolate.Language | ≥ 13.0.0&&< 13.9.16 | 13.9.16dotnet add package HotChocolate.Language --version 13.9.16 |
| .NETNuGet | HotChocolate.Language | ≥ 14.0.0&&< 14.3.1 | 14.3.1dotnet add package HotChocolate.Language --version 14.3.1 |
| .NETNuGet | HotChocolate.Language | ≥ 15.0.0&&< 15.1.14 | 15.1.14dotnet add package HotChocolate.Language --version 15.1.14 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for HotChocolate.Language, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update HotChocolate.Language to 12.22.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40324 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-40324 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-40324. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-40324 in your dependencies?
O3 Security finds CVE-2026-40324 across NuGet dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.