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GHSA-w567-gjr2-hm5j

GHSA-w567-gjr2-hm5j is a CWE-770 vulnerability in MessagePack. O3 Security confirms whether GHSA-w567-gjr2-hm5j is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

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

Also known asCVE-2026-48514
Published
Jun 25, 2026
Updated
Jun 25, 2026
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed

Real-World Exposure

2 pkgs affected
.NETMessagePack.NETMessagePack

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects NuGet packages — download data is not available via public APIs for these ecosystems.

Description

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 value is pure wire input and the allocation happens before the formatter verifies that the declared bytes are actually present in the extension body.

Affected components

  • Package: MessagePack.UnityClient
  • Resolvers: UnityBlitResolver, UnityBlitWithPrimitiveArrayResolver
  • API: UnsafeBlitFormatterBase<T>.Deserialize
  • Finding IDs: MESSAGEPACKCSHARP-080, duplicate/open variant MESSAGEPACKCSHARP-OPEN-010

Patches

Fixes are prepared and will be released in coordinated patch versions.

Upgrade guidance:

  1. Upgrade MessagePack.UnityClient to the patched version for your release line.
  2. Upgrade companion MessagePack packages in the same dependency graph to the coordinated patched versions.

The fix should validate byteLength before allocation. It should reject negative lengths, lengths greater than the extension body length after metadata, and lengths that are not a valid multiple of the element size.

Workarounds

Patching is recommended.

Until a patched version is available, do not use Unity blit resolvers on data received from untrusted peers. Use safer resolvers or explicitly validate and size-limit messages before deserialization.

Resources

  • MESSAGEPACKCSHARP-080: unsafe blit formatter allocation from unbounded byte length
  • MESSAGEPACKCSHARP-OPEN-010: duplicate/open finding for the same root cause
  • CWE-770: Allocation of Resources Without Limits or Throttling

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
.NETNuGetMessagePackall versions2.5.301
.NETNuGetMessagePack≥ 3.0&&< 3.1.73.1.7

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for MessagePack. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

  2. Fix

    Update MessagePack to 2.5.301 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-w567-gjr2-hm5j is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 pinpoints whether GHSA-w567-gjr2-hm5j is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to GHSA-w567-gjr2-hm5j. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

## 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
O3 Security · Impact-Aware SCA

Is GHSA-w567-gjr2-hm5j in your dependencies?

O3 detects GHSA-w567-gjr2-hm5j across NuGet dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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