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MessagepackApplication

CVE-2026-48502

HIGH · 7.5 CVSS v3.1 Published 2026-06-22
Fix available
A fix is available. Upgrade to 2.5.301 / 3.1.7 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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 · unedited
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePackReader.ReadDateTime() can allocate stack memory based on an attacker-controlled MessagePack extension length. In the slow path for timestamp extension parsing, the computed tokenSize includes the extension body length from the wire and is used in a stackalloc operation before the extension length is validated as one of the valid timestamp sizes. A very small payload can claim a large timestamp extension body and cause a stack allocation large enough to trigger an uncatchable StackOverflowException, terminating the host process. 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 confidence

In MessagePackReader.ReadDateTime(), the extension body length from the wire is used directly in a stackalloc operation before validation of valid timestamp sizes. An attacker can craft a small MessagePack payload claiming a large timestamp extension body, causing stack allocation large enough to trigger an uncatchable StackOverflowException that terminates the host process.

MitigationUpgrade MessagePack for C# to version 2.5.301 or 3.1.7 or later, which validates the extension length before using it in stack allocation.

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
MessagepackApplication
Affected:< 2.5.301>= 3.0.3, < 3.1.7

CVSS 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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify if MessagePack for C# is used
    Search project files (.csproj, packages.config) for MessagePack package reference, or scan deployed binaries for 'msgpack.dll' or 'MessagePack' namespace
    Affected if MessagePack library is present in the environment
  2. Determine installed MessagePack version
    Check the package version in .csproj, packages.config, or inspect the loaded MessagePack assembly's FileVersion attribute
    Affected if Version is less than 2.5.301, or between 3.0.3 and 3.1.6 inclusive
  3. Verify if timestamp deserialization occurs
    Review code that calls MessagePackSerializer.Deserialize or uses MessagePackReader.ReadDateTime with untrusted input
    Affected if The application deserializes MessagePack payloads containing timestamp extension values from external or untrusted sources

User is affected if MessagePack for C# version falls within the vulnerable ranges AND the application deserializes timestamp data from potentially malicious MessagePack payloads.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 2.5.301 / 3.1.7 or later
Fixed in 2.5.3013.1.7
Interim mitigation

Upgrade MessagePack for C# to version 2.5.301 or 3.1.7 or later, which validates the extension length before using it in stack allocation.

Recommended fix High confidence

MessagePack-CSharp 2.5.301 (for v2.x users) or MessagePack-CSharp 3.1.7 (for v3.x users)

  1. Identify the current MessagePack-CSharp version in your project (check .csproj, packages.config, or .NET dependency management)
  2. If using version 2.x (e.g., 2.0-2.5.x), upgrade to version 2.5.301
  3. If using version 3.x (e.g., 3.0.3-3.1.x), upgrade to version 3.1.7
  4. Update the package reference in your project file: dotnet add package MessagePack --version <fixed-version> or update the version in packages.config/NuGet reference
  5. Rebuild the project to verify the new package version is resolved
  6. Run existing tests, particularly any tests involving MessagePackReader.ReadDateTime() or DateTime deserialization, to confirm the fix works correctly
Caveat Review release notes between your current version and the target fixed version for any breaking changes in serialization behavior or API modifications

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Messagepack Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,720
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-48502 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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