GHSA-wfr3-xj75-pfwh — MessagePack
GHSA-wfr3-xj75-pfwh is a remote code execution vulnerability in MessagePack. A fix is available for MessagePack — see the affected versions and patch details below.
MessagePack-CSharp: DynamicUnionResolver-generated deserializers miss depth enforcement
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.
- A successful exploit gives an attacker total control of the affected component, not partial access.
- 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-wfr3-xj75-pfwh.
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.
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
Runtime-generated union deserializers emitted by DynamicUnionResolver do not call MessagePackSecurity.DepthStep(ref reader) and do not decrement reader.Depth around recursive deserialization and skip paths.
This means union deserialization does not consistently participate in the maximum object graph depth enforcement that protects other recursive formatter paths. For unknown union keys, the emitted deserializer calls reader.Skip() on attacker-controlled data without an enclosing depth step.
Impact
Applications are affected when they deserialize untrusted payloads into object graphs containing [Union]-decorated interfaces or abstract classes handled by DynamicUnionResolver.
An attacker can provide a union payload with an unknown key and a deeply nested value. Because the generated union formatter does not enter the depth accounting scope before skipping or recursively processing the value, configured depth limits can be bypassed. In combination with recursive skip behavior, this can terminate the process with an uncatchable StackOverflowException.
This issue is narrower than the general TrySkip() recursion issue because it specifically concerns a formatter-generation path that fails to count union nesting. It remains independently fixable because the emitted IL should mirror the depth-step behavior used by source-generated union formatters and dynamic object formatters.
Affected components
- Package:
MessagePack - API:
DynamicUnionResolver.BuildDeserialize - Data types:
[Union]-decorated interface and abstract class hierarchies handled by the dynamic resolver - Finding ID:
MESSAGEPACKCSHARP-070
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 emit DepthStep and matching reader.Depth-- cleanup in dynamic union deserializers, consistent with other recursive formatter implementations.
Workarounds
Patching is recommended.
Until a patched version is available, avoid deserializing untrusted payloads into dynamically resolved [Union] types. Prefer source-generated formatters that include depth checks, where applicable, and enforce outer message-size and schema constraints.
Resources
MESSAGEPACKCSHARP-070: dynamic union deserializer missing depth-step enforcement- CWE-674: Uncontrolled Recursion
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 |
Detection & 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-wfr3-xj75-pfwh 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 GHSA-wfr3-xj75-pfwh can be triaged on real exposure rather than presence alone.
Tailored to GHSA-wfr3-xj75-pfwh. 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-wfr3-xj75-pfwh in your dependencies?
O3 Security finds GHSA-wfr3-xj75-pfwh across NuGet dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.