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MessagepackApplication

CVE-2026-48515

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, MessagePack-CSharp's multi-dimensional array formatters read dimension lengths directly from the payload and allocate T[,], T[,,], or T[,,,] before validating that the dimension product matches the encoded element count. The formatter reads a guarded element array header, but allocation of the target multi-dimensional array happens before the dimensions are checked against that element count. A small payload can therefore declare large dimensions, provide an empty or tiny inner array, and cause a large heap allocation before element data is validated. 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

MessagePack-CSharp's multi-dimensional array formatters allocate memory for arrays (T[,], T[,,], T[,,,]) based on dimension lengths read directly from the payload BEFORE validating that the dimension product matches the encoded element count. An attacker can craft a small payload declaring large dimensions with an empty/tiny inner array, causing excessive heap allocation (heap exhaustion/DoS).

MitigationUpgrade MessagePack-CSharp to version 2.5.301 or 3.1.7 or later, which includes validation of dimensions against element count before array 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 MessagePack-CSharp installation
    Search your project dependencies (e.g., csproj file, packages.config, or NuGet package manager) for 'MessagePack' or 'Messagepack' package and note the version number
    Affected if The installed version is less than 2.5.301, or greater than or equal to 3.0.3 but less than 3.1.7
  2. Locate the specific MessagePack DLL or package
    If using a compiled deployment, search for 'MessagePack*.dll' files in your application directory and check their version properties (right-click > Properties > Details > File Version)
    Affected if The DLL version matches the vulnerable ranges above
  3. Determine if multi-dimensional array deserialization is used
    Search your codebase for deserialization calls that handle T[,], T[,,], or T[,,,] types (e.g., MessagePackSerializer.Deserialize<T[,]>(), generic type parameters with multiple commas)
    Affected if Your application deserializes multi-dimensional array types from untrusted input sources
  4. Check if input sources are untrusted
    Review where MessagePack deserialization occurs and identify if data comes from network sources, user uploads, API endpoints, or other external inputs
    Affected if Deserialized data originates from untrusted or network sources without prior validation
  5. Inspect runtime configuration for unsafe deserialization
    Examine your MessagePack serializer configuration (MessagePackSerializerOptions) for any settings that disable validation or enable fast paths that skip integrity checks
    Affected if Configuration disables recommended safety checks or uses custom formatters that bypass standard validation

You are affected if you run a vulnerable MessagePack-CSharp version (below 2.5.301 or 3.0.3-3.1.6) AND deserialize multi-dimensional arrays from untrusted sources.

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-CSharp to version 2.5.301 or 3.1.7 or later, which includes validation of dimensions against element count before array allocation.

Recommended fix High confidence

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

  1. Identify the current version of MessagePack-CSharp in use by checking the project dependencies (e.g., package.config, .csproj, or .nuspec file)
  2. If using version 2.x (any version < 2.5.301), upgrade to version 2.5.301
  3. If using version 3.x (version 3.0.3 through 3.1.6), upgrade to version 3.1.7
  4. Update the package reference in the project file: Update-Package MessagePack or manually edit the version number to the appropriate fixed release
  5. Verify the upgrade by rebuilding the project and running existing tests to ensure compatibility
  6. Re-deploy the updated application

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

Fix this in Messagepack Scoped from the published advisory
  • Consultation3.0 h
  • Implementation3.0 h
  • Testing6.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,400
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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-2026-48515 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