CVE-2026-48509

Summary

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.

Affected Software

VendorProductVersion RangeStatus
MessagePack-CSharpMessagePack-CSharp>= 3.0, < 3.1.7affected
MessagePack-CSharpMessagePack-CSharp< 2.5.301affected

Weaknesses

  • CWE-1188: CWE-1188: Insecure Default Initialization of Resource

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

References