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GHSA-hv8m-jj95-wg3x

HighCVSS 8.2 / 10
Published Jun 11, 2026·Last modified Jun 11, 2026
Affected Components(0)

No affected components available

Description

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
Risk Scores
Base Score
8.2

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the confidentiality of the information. There is a high impact on the availability of the system.

Threat Intelligence
7.5

Exploitation activity has been observed. Apply available patches or mitigations urgently.

EPSS
0.51%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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High severity
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