What’s Vulnerable › Vulnerabilities
CVE-2026-48109: MessagePack-CSharp: LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad input
- Severity: high (CVSS 8.2 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.5% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-06-22 · updated 2026-06-23
- Weakness: CWE-20
Description
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, A vulnerability exists in the optional LZ4 decompression path used by MessagePack compression modes Lz4Block and Lz4BlockArray. The decoder implementation is based on a deprecated fast-decompression algorithm that does not take a source-length bound. A remote attacker can send a crafted MessagePack payload with manipulated LZ4 token/length fields to force out-of-bounds reads from the compressed input buffer. In affected environments, this can trigger an AccessViolationException during decompression, causing process termination (denial of service). Under some conditions, limited unintended memory disclosure from over-read data may also be possible before failure. This vulnerability is fixed in 2.5.301 and 3.1.7.
Affected products
- MessagePack-CSharp: before 2.5.301; from 3.0.3 before 3.1.7 — fixed in 2.5.301, 3.1.7
How to fix
Upgrade to a fixed version: MessagePack-CSharp 2.5.301, 3.1.7. Check the vendor advisory for mitigations.
References
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