CVE-2026-48502: 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, MessagePackReader.ReadDateTime() can allocate stack memory based on an attacker-controlled MessagePack extension length. In the slow path for timestamp extension parsing, the computed tokenSize includes the extension body length from the wire and is used in a stackalloc operation before the extension length is validated as one of the valid timestamp sizes. A very small payload can claim a large timestamp extension body and cause a stack allocation large enough to trigger an uncatchable StackOverflowException, terminating the host process. 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 2026-06-23.