CVE-2026-48513
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedMessagePack 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceMessagePack for C# versions before 2.5.301 and 3.1.7 have a depth check bypass in DynamicUnionResolver-generated deserializers. The runtime-generated union deserializers fail to call MessagePackSecurity.DepthStep() and don't decrement reader.Depth around recursive deserialization paths, allowing attacker-controlled nested data to bypass object graph depth limits. Unknown union keys call reader.Skip() without enclosing depth protection, enabling potential stack exhaustion via deeply nested payloads.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 2.5.301>= 3.0.3, < 3.1.7CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify MessagePack for C# versionCheck the NuGet package reference in your project file (.csproj) or look at the deployed MsgPack.dll/MessagePack.dll assembly version property. In .NET, you can also run: [System.Reflection.Assembly.Load("MessagePack").GetName().Version] in a PowerShell script against the deployed binaries.Affected if The installed version is below 2.5.301 OR between 3.0.3 and 3.1.6 inclusive.
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Locate DynamicUnionResolver usageSearch your codebase for DynamicUnionResolver in source code or compiled assemblies. Look for usages like [MessagePack.Union(key, typeof(T))] attributes or calls to UnionResolver/DynamicUnionResolver in serialization configuration.Affected if DynamicUnionResolver is registered or auto-registered in your MessagePack serializer options.
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Check if union types deserialize untrusted dataReview code paths that call MessagePackSerializer.Deserialize() on data from untrusted sources (network input, user uploads, external APIs). Identify if any of these deserialization targets use union types.Affected if Your application deserializes MessagePack data from untrusted sources into types resolved via DynamicUnionResolver.
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Verify depth limit configurationInspect your MessagePack serializer options for MessagePackSecurity.DepthLimit property. Default is 64. Check if your application explicitly sets or overrides this limit.Affected if Depth limit is set but DynamicUnionResolver is used with untrusted input, as the bypass circumvents this limit.
You are affected if your deployed MessagePack for C# version is in the vulnerable range AND you deserialize untrusted MessagePack data into types using DynamicUnionResolver or dynamic union handling.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped2.5.3013.1.7
Upgrade MessagePack for C# to version 2.5.301 or 3.1.7 or later. If immediate patching is not possible, implement application-layer input validation and depth limiting before deserializing untrusted MessagePack data.
MessagePack 2.5.301 (for v2.x) or 3.1.7 (for v3.x)
- Identify the current MessagePack version in use by checking the project dependencies (e.g., in .csproj, packages.config, or similar)
- If using MessagePack v2.x, upgrade to version 2.5.301 or later
- If using MessagePack v3.x, upgrade to version 3.1.7 or later
- Update the package reference in your dependency file (e.g., dotnet add package MessagePack or update version in .csproj)
- Run build and tests to verify the upgrade does not introduce issues
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation1.0 h
- Testing4.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-48513 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-48513 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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