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Medium, CVSS 5.3

Nerdbank.MessagePack has Inefficient CPU Computation

GHSA-92vj-hp7m-gwcj

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (nerdbank.messagepack 1.2.4), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
EPSS
No dated EPSS signal available.
Source description

As published by the source; long descriptions are shortened.

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: 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.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-92vj-hp7m-gwcj

Agent brief

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# Patch Next advisory brief: GHSA-92vj-hp7m-gwcj

Advisory: Nerdbank.MessagePack has Inefficient CPU Computation
IDs: GHSA-92vj-hp7m-gwcj
Record: https://patchnext.com/advisories/ghsa-92vj-hp7m-gwcj (revision 1, source checked 26 Oct 2026, 17:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nerdbank.messagepack 1.2.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet nerdbank.messagepack: affected < 1.2.4; fixed in 1.2.4

## Suggested inspection (read-only)
- NuGet nerdbank.messagepack: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nerdbank.messagepack.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-92vj-hp7m-gwcj (GitHub-reviewed advisory GHSA-92vj-hp7m-gwcj lists affected ranges: NuGet nerdbank.messagepack >=0 <1.2.4)

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