---
id: CVE-2026-48109
aliases:
  - GHSA-hv8m-jj95-wg3x
title: ' MessagePack''s LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad input'
summary: ' MessagePack''s LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad input'
severity: high
cvss: 8.2
cwe:
  - CWE-20
vendor: MessagePack
product: MessagePack
ecosystem: nuget
affected:
  - MessagePack < 2.5.301
  - 'MessagePack >= 3.0.214-rc.1, < 3.1.7'
patched:
  - MessagePack 2.5.301
  - MessagePack 3.1.7
published: '2026-06-11'
updated: '2026-06-25'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-hv8m-jj95-wg3x'
references:
  - url: >-
      https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-hv8m-jj95-wg3x
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-48109'
  - url: 'https://github.com/advisories/GHSA-hv8m-jj95-wg3x'
tags:
  - ghsa
  - nuget
epss: 0.00509
epssPercentile: 0.41038
ingestedAt: '2026-07-07T15:41:59.277Z'
---

## Overview

### Impact

A vulnerability exists in the optional LZ4 decompression path used by MessagePack compression modes `Lz4Block` and `Lz4BlockArray`.

The decoder implementation is based on a deprecated fast-decompression algorithm that does not take a source-length bound. A remote attacker can send a crafted MessagePack payload with manipulated LZ4 token/length fields to force out-of-bounds reads from the compressed input buffer. In affected environments, this can trigger an `AccessViolationException` during decompression, causing process termination (denial of service). Under some conditions, limited unintended memory disclosure from over-read data may also be possible before failure.

This issue affects applications that deserialize untrusted data while LZ4 compression is enabled.

### Patches

The v2 versions are patched as of 2.5.301.
The v3 versions are patched as of 3.1.7.

### Workarounds

Instead of upgrading, an application may take the following precautions:

1. Disable LZ4 compression for untrusted input paths (`Lz4Block`, `Lz4BlockArray`).
2. Only accept compressed payloads from strongly trusted producers.
3. Isolate deserialization in a separate process/container with restart supervision to limit availability impact.

### Resources

- MESSAGEPACKCSHARP-010

## Affected packages

- `MessagePack < 2.5.301`
- `MessagePack >= 3.0.214-rc.1, < 3.1.7`

## Remediation

Upgrade to a patched release:

- `MessagePack 2.5.301`
- `MessagePack 3.1.7`