GHSA-vh6j-jc39-fggf
HIGHGHSA-vh6j-jc39-fggf is a high-severity (CVSS 7.5) CWE-674 vulnerability in MessagePack. O3 Security confirms whether GHSA-vh6j-jc39-fggf is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
MessagePack-CSharp: MessagePackReader.Skip can recurse without enforcing maximum object graph depth
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 GHSA-vh6j-jc39-fggf.
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
GHSA-vh6j-jc39-fggf 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 358,648 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
MessagePack.NETMessagePackReal-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
Summary
MessagePackReader.TrySkip() recursively descends into nested arrays and maps without incrementing the reader depth or calling the configured depth checks. This bypasses MessagePackSecurity.MaximumObjectGraphDepth, the library's documented protection against deeply nested object graphs.
Many generated and dynamic formatters call reader.Skip() when they encounter unknown map keys, unknown array members, ignored fields, or data that should be skipped for forward compatibility. A deeply nested value in one of these skipped positions can therefore cause unbounded recursion and an uncatchable StackOverflowException.
Impact
Applications that deserialize untrusted MessagePack payloads are affected when a formatter skips attacker-controlled values. This is a broad deserialization path and can be reached during normal object deserialization when an input includes an unknown member or extra value.
The attacker does not need to target a special resolver or compression mode. A payload containing many nested single-element arrays or maps in a skipped location can exhaust the process stack. Because StackOverflowException is not catchable in normal .NET execution, this terminates the host process and can deny service to other users of the same process.
MessagePackSecurity.UntrustedData does not mitigate this issue because the skip path does not participate in depth accounting.
Affected components
- Package:
MessagePack - APIs:
MessagePackReader.Skip,MessagePackReader.TrySkip, and formatter paths that skip unknown or ignored values - Finding IDs:
MESSAGEPACKCSHARP-021, duplicate/open variantMESSAGEPACKCSHARP-OPEN-001
Patches
Fixes are prepared and will be released in coordinated patch versions.
Upgrade guidance:
- Upgrade
MessagePackto the patched version for your release line. - Upgrade companion MessagePack packages in the same dependency graph to the coordinated patched versions.
The fix should either make skip traversal iterative or apply the existing depth accounting to arrays and maps encountered by TrySkip(). Any exceeded depth limit should result in a catchable serialization exception instead of process stack exhaustion.
Workarounds
Patching is recommended.
There is no complete workaround for applications that deserialize untrusted MessagePack payloads with affected versions. Reducing accepted message sizes can raise the cost of exploitation but does not remove the recursive skip behavior. Strict schema validation outside MessagePack-CSharp may help only if it rejects unknown or skipped fields before the serializer sees them.
Resources
MESSAGEPACKCSHARP-021: unbounded recursion inTrySkip()MESSAGEPACKCSHARP-OPEN-001: duplicate/open finding for the same root cause- CWE-674: Uncontrolled Recursion
CVE split rationale
This vulnerability is independently fixable in the skip traversal implementation. It should be tracked separately from formatter-specific missing depth checks, JSON conversion recursion, and non-recursion allocation bugs.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | MessagePack | all versions | 2.5.301 |
| .NETNuGet | MessagePack | ≥ 3.0&&< 3.1.7 | 3.1.7 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for MessagePack. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update MessagePack to 2.5.301 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-vh6j-jc39-fggf 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 pinpoints whether GHSA-vh6j-jc39-fggf is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-vh6j-jc39-fggf. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-vh6j-jc39-fggf in your dependencies?
O3 detects GHSA-vh6j-jc39-fggf across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.