Vulnerability-Lookup

CVE-2026-48109 (GCVE-0-2026-48109)

Vulnerability from cvelistv5 – Published: 2026-06-22 21:19 – Updated: 2026-06-23 12:14

Title

MessagePack-CSharp: LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad input

Summary

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, 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 vulnerability is fixed in 2.5.301 and 3.1.7.

Severity

8.2 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-20 - Improper Input Validation

Assigner

GitHub_M

References

1 reference

URL	Tags
https://github.com/MessagePack-CSharp/MessagePack…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version
MessagePack-CSharp	MessagePack-CSharp	Affected: >= 3.1.7, < 3.1.7 Affected: < 2.5.301

Show details on NVD website

JSON

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GHSA-HV8M-JJ95-WG3X

Vulnerability from github – Published: 2026-06-11 20:34 – Updated: 2026-06-25 15:01

Summary

MessagePack's LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad input

Details

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:

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

Resources

MESSAGEPACKCSHARP-010

Severity

8.2 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "NuGet",
        "name": "MessagePack"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.5.301"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "NuGet",
        "name": "MessagePack"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.214-rc.1"
            },
            {
              "fixed": "3.1.7"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-48109"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-11T20:34:10Z",
    "nvd_published_at": "2026-06-22T22:16:46Z",
    "severity": "HIGH"
  },
  "details": "### Impact\n\nA vulnerability exists in the optional LZ4 decompression path used by MessagePack compression modes `Lz4Block` and `Lz4BlockArray`.\n\nThe 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.\n\nThis issue affects applications that deserialize untrusted data while LZ4 compression is enabled.\n\n### Patches\n\nThe v2 versions are patched as of 2.5.301.\nThe v3 versions are patched as of 3.1.7.\n\n### Workarounds\n\nInstead of upgrading, an application may take the following precautions:\n\n1. Disable LZ4 compression for untrusted input paths (`Lz4Block`, `Lz4BlockArray`).\n2. Only accept compressed payloads from strongly trusted producers.\n3. Isolate deserialization in a separate process/container with restart supervision to limit availability impact.\n\n### Resources\n\n- MESSAGEPACKCSHARP-010",
  "id": "GHSA-hv8m-jj95-wg3x",
  "modified": "2026-06-25T15:01:13Z",
  "published": "2026-06-11T20:34:10Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-hv8m-jj95-wg3x"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-48109"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/MessagePack-CSharp/MessagePack-CSharp"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": " MessagePack\u0027s LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad input"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

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