CVE-2026-48515: MessagePack for C# resource exhaustion in multi-dimensional array formatters

CVE-2026-48515 · Severity: medium · CVSS 4 · Published 2026-06-22

MessagePack-CSharp is a library used to exchange data between applications. A flaw in how it handles multi-dimensional arrays allows an attacker to send a specially crafted small message that forces the application to allocate massive amounts of memory. This can lead to the application crashing, being shut down by the operating system, or becoming unresponsive, resulting in a denial-of-service.

Technologies: MessagePack-CSharp MessagePack for C#, MessagePack-CSharp, MessagePack (NuGet). Vendors: MessagePack-CSharp, NuGet.

Quick answers

Is CVE-2026-48515 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-48515 being exploited in the wild.
How severe is CVE-2026-48515?
Medium severity, with a CVSS score of 4, published 22 June 2026.
Which products and versions are affected?
MessagePack-CSharp MessagePack for C# < 2.5.301, >= 3.0 < 3.1.7; MessagePack-CSharp < 2.5.301, >= 3.0, < 3.1.7; MessagePack (NuGet) ECOSYSTEM:introduced=0,fixed=2.5.301.
Is there a fix for CVE-2026-48515?
Yes. MessagePack (NuGet): upgrade to 2.5.301 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-48515 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-48515?
Check whether you run MessagePack-CSharp MessagePack for C#, MessagePack-CSharp or MessagePack (NuGet) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • MessagePack (NuGet): upgrade to 2.5.301 or later
    dotnet add package MessagePack --version 2.5.301

Technical details

The vulnerability is a resource exhaustion issue (CWE-770) within the multi-dimensional array formatters (2D, 3D, and 4D). The root cause is that the `Deserialize` methods in `TwoDimensionalArrayFormatter<T>`, `ThreeDimensionalArrayFormatter<T>`, and `FourDimensionalArrayFormatter<T>` read dimension lengths directly from the MessagePack payload and perform heap allocation before validating that the total element count matches the actual data provided. An attacker can provide a small payload with very large dimension integers, causing the library to attempt a massive allocation. This results in OutOfMemoryExceptions, high CPU usage due to zero-initialization, or process termination. The issue is fixed in versions 2.5.301 and 3.1.7.

Affected products

  • MessagePack-CSharp MessagePack-CSharp < 2.5.301, >= 3.0, < 3.1.7

Identifiers

  • CVE-2026-48515
  • GHSA-cxmj-83gh-fp49

Timeline

  • 2026-06-09: disclosed
  • 2026-06-22: advisory: NVD publication date
  • 2026-06-25: patched: GitHub Advisory reviewed and updated

References

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