MessagePack-CSharp: Unity unsafe blit formatter allocates from unbounded byte length

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.3 · CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-48514: 0.40% estimated exploitation activity in the next 30 days; percentile 34.80 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Impact Applications are affected when they deserialize untrusted payloads using Unity blit resolvers such as UnityBlitResolver or UnityBlitWithPrimitiveArrayResolver. This is especially relevant to Unity multiplayer clients or servers that use MessagePack-CSharp for networked values such as vectors, matrices, or primitive arrays. A hostile peer can send an extension payload with a large declared byte length and cause an out-of-memory exception or process termination on memory-constrained platforms. The resolver is opt-in, but the vulnerable…

Published by the source

25 Jun 2026, 21:25 UTC

Last modified by the source

25 Jun 2026, 21:25 UTC

Source last checked

26 Oct 2026, 17:04 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-w567-gjr2-hm5j

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# Patch Next advisory brief: CVE-2026-48514

Advisory: MessagePack-CSharp: Unity unsafe blit formatter allocates from unbounded byte length
IDs: CVE-2026-48514, GHSA-w567-gjr2-hm5j
Record: https://patchnext.com/advisories/cve-2026-48514 (revision 1, source checked 26 Oct 2026, 17:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: messagepack 3.1.7, 2.5.301. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet messagepack: affected < 2.5.301; >= 3.0, < 3.1.7; fixed in 2.5.301, 3.1.7

## Suggested inspection (read-only)
- NuGet messagepack: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on messagepack.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-w567-gjr2-hm5j (GitHub-reviewed advisory GHSA-w567-gjr2-hm5j lists affected ranges: NuGet messagepack >=0 =3.0 <3.1.7)

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