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MessagepackApplication

CVE-2026-48514

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, UnsafeBlitFormatterBase<T>.Deserialize reads an attacker-controlled byteLength from an extension payload and allocates an array based on that value before validating it against the extension header length or remaining payload bytes. The outer extension header is bounded by available input, but that bound is not used to constrain the inner byteLength before allocation. A very small payload can therefore request a very large T[] allocation. 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

UnsafeBlitFormatterBase<T>.Deserialize in MessagePack for C# reads an attacker-controlled byteLength from an extension payload and allocates a T[] array based on that value before validating it against the extension header length or remaining payload bytes. Since the allocation bound is not validated against available input before allocation, a small payload can trigger allocation of a very large array, leading to excessive memory consumption or OutOfMemoryException (DoS).

MitigationUpgrade MessagePack for C# to version 2.5.301 or 3.1.7 or later. Alternatively, avoid deserializing untrusted MessagePack data using UnsafeBlitFormatterBase or implement input size limits at the application layer.

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. Locate MessagePack for C# installation
    Search for MsgPack.dll, MessagePack.dll, or the MessagePack NuGet package reference in your project files (packages.config, .csproj) orbin folder
    Affected if MessagePack for C# is not found in the project dependencies
  2. Determine installed version
    Inspect the version attribute of the MessagePack package reference, or right-click the MessagePack DLL and view Properties > Version
    Affected if Version is below 2.5.301 (for 2.x line) or 3.0.3 to 3.1.6 (for 3.x line)
  3. Identify UnsafeBlitFormatterBase usage
    Search code for usage of UnsafeBlitFormatterBase<T> or BlitFormatter types in deserialization calls, or check if custom formatters inherit from UnsafeBlitFormatterBase
    Affected if Code explicitly uses UnsafeBlitFormatterBase or custom types deriving from it for deserialization
  4. Assess data trust level
    Review the deserialization code path to determine if MessagePack data from external or untrusted sources is being deserialized (e.g., network input, user uploads, message queues)
    Affected if UnsafeBlitFormatterBase is used to deserialize data from untrusted or network sources

You are affected if you use a vulnerable version of MessagePack for C# (2.x below 2.5.301 or 3.0.3-3.1.6) AND use UnsafeBlitFormatterBase to deserialize untrusted MessagePack payloads, as this combination allows an attacker to trigger excessive memory allocation.

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. Alternatively, avoid deserializing untrusted MessagePack data using UnsafeBlitFormatterBase or implement input size limits at the application layer.

Recommended fix High confidence

MessagePack 2.5.301 (for 2.x users) or MessagePack 3.1.7 (for 3.x users)

  1. Identify which major version (2.x or 3.x) of MessagePack for C# is currently in use by checking the project dependencies
  2. For users of MessagePack 2.x: upgrade to version 2.5.301 or later
  3. For users of MessagePack 3.x: upgrade to version 3.1.7 or later
  4. Update the package reference in the project file (e.g., PackageReference Include="MessagePack" Version="2.5.301" or Version="3.1.7")
  5. Restore the updated NuGet package
  6. Rebuild the project and run tests to verify the application functions correctly with the fixed version
Caveat Minor version upgrades typically maintain backward compatibility, but test thoroughly to confirm no regressions

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

Fix this in Messagepack Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,060
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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-2026-48514 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data