Uncontrolled Recursion Affecting messagepack package, versions [,2.5.301)[3.0,3.1.7)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-DOTNET-MESSAGEPACK-17660968
- published28 Jun 2026
- disclosed25 Jun 2026
- creditAArnott
Introduced: 25 Jun 2026
NewCVE-2026-48513 (opens in a new tab)How to fix?
Upgrade MessagePack to version 2.5.301, 3.1.7 or higher.
Overview
MessagePack is a MessagePack(MsgPack) Serializer for C#(.NET, .NET Core, Unity, Xamarin).
Affected versions of this package are vulnerable to Uncontrolled Recursion in the DynamicUnionResolver.BuildDeserialize process. An attacker can cause a process crash by providing a specially crafted union payload with an unknown key and deeply nested value, which bypasses configured depth limits and leads to unbounded recursion. This is only exploitable if applications deserialize untrusted payloads into object graphs containing [Union]-decorated interfaces or abstract classes handled by the dynamic resolver.
Workaround
This vulnerability can be mitigated by avoiding deserialization of untrusted payloads into dynamically resolved [Union] types, preferring source-generated formatters with depth checks, and enforcing outer message-size and schema constraints.