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Medium · 6.3 CVE-2026-48517 EUVD-2026-38363GHSA-qhmf-xw27-6rqr

MessagePack-CSharp: Typeless deserialization type restrictions do not recurse into arrays or generic arguments

Published Jun 22, 2026 · Updated Jun 25, 2026 · Assigned by GitHub_M

Description

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePack-CSharp's typeless deserialization includes MessagePackSerializerOptions.ThrowIfDeserializingTypeIsDisallowed(Type) as a safety check for dangerous types. The default implementation checks the outer type name, but it does not recursively inspect array element types or generic type arguments. As a result, a type that would be blocked directly can be wrapped inside an array or constructed generic type and pass the outer type check. The formatter machinery can then materialize formatters for the inner blocked type. This vulnerability is fixed in 2.5.301 and 3.1.7.

Affected products

VendorProductAffectedFixed
MessagePack-CSharp MessagePack-CSharp >= 3.0, < 3.1.7, < 2.5.301 —

Fixed in Linux distributions

Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.

Azure Linux

ReleasePackageFixed inAdvisory
Azure Linux 3 python-msgpack No fix yet —

Affected packages

EcosystemPackageAffectedFixedRecord
NuGet MessagePack < 2.5.301 2.5.301 GHSA-qhmf-xw27-6rqr
NuGet MessagePack >= 3.0, < 3.1.7 3.1.7 GHSA-qhmf-xw27-6rqr

References