Vulnerability · Published Jun 22, 2026 · Assigned by GitHub_M
CVE-2026-48513MessagePack-CSharp: DynamicUnionResolver generated deserializers miss depth enforcement
Medium 6.3
In plain English
A medium-severity security flaw in MessagePack-CSharp from MessagePack-CSharp. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 35% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, runtime-generated union deserializers emitted by DynamicUnionResolver do not call MessagePackSecurity.DepthStep(ref reader) and do not decrement reader.Depth around recursive deserialization and skip paths. This means union deserialization does not consistently participate in the maximum object graph depth enforcement that protects other recursive formatter paths. For unknown union keys, the emitted deserializer calls reader.Skip() on attacker-controlled data without an enclosing depth step. This vulnerability is fixed in 2.5.301 and 3.1.7.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| NuGet | messagepack | 2.5.301 | GHSA-wfr3-xj75-pfwh |
| NuGet | messagepack | 3.1.7 | GHSA-wfr3-xj75-pfwh |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| MessagePack-CSharp | MessagePack-CSharp | >= 3.0, < 3.1.7< 2.5.301 |
Weakness: CWE-674 · Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N