PT-2026-51393 · Messagepack Csharp · Messagepack-Csharp

Published 2026-06-22 · Updated 2026-06-22 · CVE-2026-48509

Mitre

CVSS v4.0

6.3

Medium

Base vector

AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, the parameterless MessagePackInputFormatter() constructor uses default serializer options, which resolve to MessagePackSerializerOptions.Standard with MessagePackSecurity.TrustedData. The formatter is designed for ASP.NET Core MVC request bodies, which commonly cross an HTTP trust boundary. This insecure default can expose applications to denial-of-service attacks that MessagePackSecurity.UntrustedData is intended to mitigate, such as hash-collision attacks against dictionary-like model properties. This vulnerability is fixed in 2.5.301 and 3.1.7.

Fix

Weakness Enumeration

CWE-1188

Related Identifiers

CVE-2026-48509

Affected Products

Messagepack-Csharp

References · 2

• https://nvd.nist.gov/vuln/detail/CVE-2026-48509 · Security Note
• https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-2f33-pr97-265q · Note