CVE-2026-48510: MessagePack for C# denial of service via LZ4 decompression bomb

CVE-2026-48510 · Severity: high · CVSS 7.5 · Published 2026-06-22

MessagePack-CSharp is a library used to serialize and deserialize data for efficient communication between applications. A vulnerability in its LZ4 compression handling allows an attacker to send a specially crafted message that claims to be very large when decompressed. This causes the application to attempt to allocate massive amounts of memory, potentially leading to system crashes, service outages, or severe performance degradation.

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

Quick answers

Is CVE-2026-48510 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-48510 being exploited in the wild.
How severe is CVE-2026-48510?
High severity, with a CVSS score of 7.5, published 22 June 2026.
Which products and versions are affected?
MessagePack-CSharp MessagePack for C# < 2.5.301, >= 3.0.0 < 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-2026-48510?
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-2026-48510 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-48510?
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

A resource exhaustion vulnerability exists in MessagePack-CSharp's LZ4 decompression logic (Lz4Block and Lz4BlockArray). The library reads the declared uncompressed length from the incoming payload and allocates an output buffer based on this value before validating the data or checking if the expansion ratio is reasonable. An attacker can provide a small payload with a large declared length to trigger an OutOfMemoryException or process termination. This affects the MessagePackSerializer when LZ4 compression modes are enabled. Patches are available in versions 2.5.301 and 3.1.7, which introduce caps on decompressed sizes.

Affected products

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

Identifiers

  • CVE-2026-48510
  • GHSA-v72x-2h86-7f8m

Timeline

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

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.