GHSA-vh6j-jc39-fggf — MessagePack
HIGHGHSA-vh6j-jc39-fggf is a high-severity (CVSS 7.5) CWE-674 vulnerability in MessagePack. A fix is available for MessagePack — see the affected versions and patch details below.
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
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
GHSA-vh6j-jc39-fggf by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 380,066 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
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 | 2.5.301dotnet add package MessagePack --version 2.5.301 |
| .NETNuGet | MessagePack | ≥ 3.0&&< 3.1.7 | 3.1.7dotnet add package MessagePack --version 3.1.7 |
Affected Products
messagepackmessagepackDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for MessagePack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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
Stop feeding it untrusted input: reject or quarantine files and payloads from unverified sources until you can upgrade, restrict accepted formats to the ones you actually need, and run the parsing or decoding step in a least-privileged sandbox or short-lived worker so a crash or corrupted read cannot reach the rest of the process.
Frequently Asked Questions
Is GHSA-vh6j-jc39-fggf in your dependencies?
Find it across NuGet, including transitive dependencies.