Vulnerability · Published Jun 22, 2026 · Assigned by GitHub_M
CVE-2026-48510MessagePack-CSharp: LZ4 decompression allocates from unbounded declared output lengths
Medium 6.3
In plain English
A medium-severity resource allocation without limits in MessagePack-CSharp from MessagePack-CSharp. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 35% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, when MessagePack-CSharp decompresses Lz4Block or Lz4BlockArray payloads, it reads declared uncompressed lengths from the wire and allocates output buffers based on those lengths before validating that the compressed data is valid or that the declared expansion is reasonable. A small payload can claim a very large uncompressed length and force a large allocation before LZ4 decoding begins. This vulnerability is fixed in 2.5.301 and 3.1.7.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| NuGet | messagepack | 2.5.301 | GHSA-v72x-2h86-7f8m |
| NuGet | messagepack | 3.1.7 | GHSA-v72x-2h86-7f8m |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| MessagePack-CSharp | MessagePack-CSharp | >= 3.0, < 3.1.7< 2.5.301 |
Weakness: CWE-409, CWE-770 · Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N