CVE-2026-48513: medium-severity vulnerability in MessagePack-CSharp
MessagePack-CSharp: DynamicUnionResolver generated deserializers miss depth enforcement
Published · Updated
13Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 6.3epss 0.4%
exploitation probability
0.4%top 67% of all CVEs
observed exploitation
nono source reports it
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.
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
Affected products
MessagePack-CSharp · MessagePack-CSharpRelated CVEs — MessagePack-CSharp
In the same product, most dangerous first.
CVE-2026-48109HIGHMessagePack-CSharp: LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad inputEPSS 0.5%CVE-2026-48506HIGHMessagePack-CSharp: MessagePackReader.Skip can recurse without enforcing maximum object graph depthEPSS 0.5%CVE-2026-48502HIGHMessagePack-CSharp: Denial of service vulnerabilities can swamp the CPU or crash the process with stack and heap overflowsEPSS 0.4%CVE-2026-48509MEDIUMMessagePack-CSharp: ASP.NET Core MessagePackInputFormatter defaults to TrustedData for HTTP request bodiesEPSS 0.4%CVE-2026-48510MEDIUMMessagePack-CSharp: LZ4 decompression allocates from unbounded declared output lengthsEPSS 0.4%CVE-2026-48511MEDIUMMessagePack-CSharp: ExpandoObject formatter can perform quadratic insertion work on untrusted mapsEPSS 0.4%