GHSA-wfr3-xj75-pfwh
GHSA-wfr3-xj75-pfwh is a CWE-674 vulnerability in MessagePack. O3 Security confirms whether GHSA-wfr3-xj75-pfwh is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
MessagePack-CSharp: DynamicUnionResolver-generated deserializers miss depth enforcement
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 | 2.5.301 |
| .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-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 pinpoints whether GHSA-wfr3-xj75-pfwh 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-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 detects GHSA-wfr3-xj75-pfwh across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.