Vulnerability 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.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Messagepack | Messagepack | < 2.5.301 |
Related Weaknesses (CWE)
References
- https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSMitigationVendor Advisory
FAQ
What is CVE-2026-48109?
CVE-2026-48109 is a vulnerability with a CVSS score of 8.2 (HIGH). 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 Lz4B...
How severe is CVE-2026-48109?
CVE-2026-48109 has been rated HIGH with a CVSS base score of 8.2/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-48109?
Check the references section above for vendor advisories and patch information. Affected products include: Messagepack Messagepack.