GHSA-92vj-hp7m-gwcj
MEDIUMNerdbank.MessagePack has Inefficient CPU Computation
Blast Radius
Nerdbank.MessagePackReal-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
Applications that call OptionalConverters.WithExpandoObjectConverter and deserialize untrusted data are open to a vulnerability by which an attacker can exploit a O(n²) algorithm to burn an inordinate amount of CPU effort by adding a great many properties to an ExpandoObject, whose Add method is implemented as an O(n) algorithm.
Patches
Update to a patched version.
If a project's ExpandoObject data requires more than 128 properties, the default limit should be changed:
this.Serializer = this.Serializer with
{
StartingContext = this.Serializer.StartingContext with
{
Security = this.Serializer.StartingContext.Security with
{
ExpandoObjectMaxPropertyCount = 256, // Set this to whatever limit is required by your application
},
},
};
Workarounds
Avoid the non-default WithExpandoObjectConverter extension method when deserializing untrusted data.
If deserializing untrusted data into an ExpandoObject is required, developers should write a custom converter for their project that limits the number of properties allowed before initializing the object.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| .NETNuGet | Nerdbank.MessagePack | all versions | 1.2.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for Nerdbank.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 Nerdbank.MessagePack to 1.2.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-92vj-hp7m-gwcj 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-92vj-hp7m-gwcj 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-92vj-hp7m-gwcj. 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-92vj-hp7m-gwcj in your dependencies?
O3 detects GHSA-92vj-hp7m-gwcj across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.