Quick answers
- Is CVE-2026-48109 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-48109 being exploited in the wild.
- How severe is CVE-2026-48109?
- High severity, with a CVSS score of 8.2, published 22 June 2026.
- Which products and versions are affected?
- MessagePack-CSharp MessagePack for C# < 2.5.301, >= 3.0.0 < 3.1.7, < 2.5.301, >= 3.0.214-rc.1, < 3.1.7; MessagePack (NuGet) ECOSYSTEM:introduced=0,fixed=2.5.301.
- Is there a fix for CVE-2026-48109?
- 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-2026-48109 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-48109?
- Check whether you run MessagePack-CSharp MessagePack for C# 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
An out-of-bounds read vulnerability exists in the LZ4 decompression implementation of MessagePack for C#. The root cause is the use of a deprecated fast-decompression algorithm that lacks source-length bound checks. A remote, unauthenticated attacker can exploit this by sending a crafted MessagePack payload with manipulated LZ4 token or length fields. This can result in an AccessViolationException, leading to process termination (Denial of Service), and potentially limited memory disclosure of over-read data. The issue is fixed in versions 2.5.301 and 3.1.7.
Affected products
- MessagePack-CSharp MessagePack for C# < 2.5.301, >= 3.0.0 < 3.1.7
Identifiers
- CVE-2026-48109
- GHSA-hv8m-jj95-wg3x
Timeline
- 2026-06-09: advisory: GitHub advisory published
- 2026-06-22: disclosed: NVD publication date