CVE-2026-48510
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, when MessagePack-CSharp decompresses Lz4Block or Lz4BlockArray payloads, it reads declared uncompressed lengths from the wire and allocates output buffers based on those lengths before validating that the compressed data is valid or that the declared expansion is reasonable. A small payload can claim a very large uncompressed length and force a large allocation before LZ4 decoding begins. 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-CSharp deserializes Lz4Block and Lz4BlockArray payloads by reading declared uncompressed lengths from the wire and pre-allocating buffers before any validation. An attacker can craft a small compressed payload claiming an excessively large uncompressed size, triggering disproportionate memory allocation (similar to a zip bomb), causing denial of service.
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 installed MessagePack-CSharp versionCheck the version of the MessagePack-CSharp package in your project dependencies (via NuGet package manager, .csproj file, or running 'dotnet list package')Affected if Version is less than 2.5.301, or between 3.0.3 and 3.1.6 inclusive
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Determine if Lz4Block or Lz4BlockArray deserialization is usedSearch your codebase for references to Lz4Block, Lz4BlockArray, or Lz4Options in deserialization code; examine MessagePackSerializer.Deserialize calls using Lz4 compression optionsAffected if Code deserializes Lz4Block or Lz4BlockArray payloads
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Assess source of deserialized dataAudit whether the Lz4Block/Lz4BlockArray deserialization processes data from untrusted external sources such as network endpoints, user input, or files from untrusted originAffected if Data from untrusted sources is deserialized using Lz4 compression
You are affected if your MessagePack-CSharp version is vulnerable (below 2.5.301 or 3.0.3-3.1.6) AND your application deserializes Lz4Block or Lz4BlockArray payloads from untrusted sources
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-CSharp to version 2.5.301 or 3.1.7 or later. If upgrading is not feasible, disable acceptance of Lz4Block/Lz4BlockArray payloads from untrusted sources.
2.5.301 for 2.x users; 3.1.7 for 3.x users
- Identify which major version branch of MessagePack-CSharp you are currently using (2.x or 3.x)
- For 2.x branch users: Upgrade to version 2.5.301 or later
- For 3.x branch users: Upgrade to version 3.1.7 or later
- Update the package reference in your project file (e.g., dotnet add package MessagePack --version <fixed-version>)
- Rebuild your solution and run tests to verify the upgrade does not break functionality
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-2026-48510 — 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-2026-48510 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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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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