GHSA-92VJ-HP7M-GWCJ

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.

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.

GHSA-92VJ-HP7M-GWCJ has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.2.4); upgrading removes the vulnerable code path.

Kodem intelligence

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
		},
	},
};

1. What is GHSA-92VJ-HP7M-GWCJ? GHSA-92VJ-HP7M-GWCJ is a medium-severity security vulnerability in Nerdbank.MessagePack (nuget), affecting versions < 1.2.4. It is fixed in 1.2.4.
2. How severe is GHSA-92VJ-HP7M-GWCJ? GHSA-92VJ-HP7M-GWCJ has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of Nerdbank.MessagePack are affected by GHSA-92VJ-HP7M-GWCJ? Nerdbank.MessagePack (nuget) versions < 1.2.4 is affected.
4. Is there a fix for GHSA-92VJ-HP7M-GWCJ? Yes. GHSA-92VJ-HP7M-GWCJ is fixed in 1.2.4. Upgrade to this version or later.
5. Is GHSA-92VJ-HP7M-GWCJ exploitable, and should I be worried? Whether GHSA-92VJ-HP7M-GWCJ is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether GHSA-92VJ-HP7M-GWCJ is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix GHSA-92VJ-HP7M-GWCJ? Upgrade Nerdbank.MessagePack to 1.2.4 or later.