CVE-2026-48515: Messagepack

High severity, CVSS 7.5. EPSS: 0.4% chance of exploitation in the next 30 days.

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePack-CSharp's multi-dimensional array formatters read dimension lengths directly from the payload and allocate T[,], T[,,], or T[,,,] before validating that the dimension product matches the encoded element count. The formatter reads a guarded element array header, but allocation of the target multi-dimensional array happens before the dimensions are checked against that element count. A small payload can therefore declare large dimensions, provide an empty or tiny inner array, and cause a large heap allocation before element data is validated. This vulnerability is fixed in 2.5.301 and 3.1.7.

Affected products

• Messagepack Messagepack: before 2.5.301 (fixed in 2.5.301); from 3.0.3, before 3.1.7 (fixed in 3.1.7)

Published 2026-06-22. Last modified 2026-06-25.