Untrusted data can lead to DoS attack due to hash collisions and stack overflow in MessagePack

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.8 · CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:N/A:H

EPSS

• CVE-2020-5234: 1.58% estimated exploitation activity in the next 30 days; percentile 75.51 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact When this library is used to deserialize messagepack data from an untrusted source, there is a risk of a denial of service attack by either of two vectors: 1. hash collisions - leading to large CPU consumption disproportionate to the size of the data being deserialized. 1. stack overflow - leading to the deserializing process crashing. Patches The following steps are required to mitigate this risk. 1. Upgrade to a version of the library where a fix is available 1. Add code to your application to put MessagePack into the defensive UntrustedData mode. 1. Identify all MessagePack extensions that implement IMessagePackFormatter<T implementations that do not ship with the MessagePack library to include the security mitigations. This includes those acquired from 3rd party packages and classes included directly into your project. Any AOT formatters generated with the MPC tool must be regenerated with the patched version of mpc. 1. Review your messagepack-serializable data structures…

Published by the source

31 Jan 2020, 17:59 UTC

Last modified by the source

16 Oct 2024, 22:07 UTC

Source last checked

26 Oct 2026, 17:00 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-7q36-4xx7-xcxf

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# Patch Next advisory brief: CVE-2020-5234

Advisory: Untrusted data can lead to DoS attack due to hash collisions and stack overflow in MessagePack
IDs: CVE-2020-5234, GHSA-7q36-4xx7-xcxf
Record: https://patchnext.com/advisories/cve-2020-5234 (revision 1, source checked 26 Oct 2026, 17:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: messagepack 2.1.90, 1.9.11; messagepack.immutablecollection 2.1.90, 1.9.11; messagepack.unity 2.1.90, 1.9.11; messagepack.unityshims 2.1.90, 1.9.11; messagepack.reactiveproperty 2.1.90, 1.9.11. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet messagepack: affected < 1.9.11; >= 2.0.0, < 2.1.90; fixed in 1.9.11, 2.1.90
- NuGet messagepack.immutablecollection: affected < 1.9.11; >= 2.0.0, < 2.1.90; fixed in 1.9.11, 2.1.90
- NuGet messagepack.unity: affected < 1.9.11; >= 2.0.0, < 2.1.90; fixed in 1.9.11, 2.1.90
- NuGet messagepack.unityshims: affected < 1.9.11; >= 2.0.0, < 2.1.90; fixed in 1.9.11, 2.1.90
- NuGet messagepack.reactiveproperty: affected < 1.9.11; >= 2.0.0, < 2.1.90; fixed in 1.9.11, 2.1.90

## Suggested inspection (read-only)
- NuGet messagepack: check the installed version with your package manager.
- NuGet messagepack.immutablecollection: check the installed version with your package manager.
- NuGet messagepack.unity: check the installed version with your package manager.
- NuGet messagepack.unityshims: check the installed version with your package manager.
- NuGet messagepack.reactiveproperty: 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 messagepack, messagepack.immutablecollection, messagepack.unity, messagepack.unityshims, messagepack.reactiveproperty.
- 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-7q36-4xx7-xcxf (GitHub-reviewed advisory GHSA-7q36-4xx7-xcxf lists affected ranges: NuGet messagepack >=0 =2.0.0 =0 =2.0.0 =0 =2.0.0 =0 =2.0.0 =0 =2.0.0 <2.1.90)

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