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TI-2026-35549 Aliases CVE-2026-48109GHSA-hv8m-jj95-wg3x

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

Priority MEDIUM 42CWE-20Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
Low · None · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub.

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00509 43rd percentileScored 2026-11-07
Fix Fixed MessagePack-CSharp (MessagePack-CSharp): 3.1.7, 2.5.301MessagePack (NuGet): 2.5.301, 3.1.7

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
MessagePack-CSharpMessagePack-CSharp3.1.7 to before 3.1.7; before 2.5.3013.1.7, 2.5.301Patch availableCNA
—MessagePack (NuGet)before 2.5.3012.5.301Patch availableGHSA-hv8m-jj95-wg3x
—MessagePack (NuGet)3.0.214-rc.1 to before 3.1.73.1.7Patch availableGHSA-hv8m-jj95-wg3x
  • MessagePack-CSharp VendorMessagePack-CSharp Affected 3.1.7 to before 3.1.7; before 2.5.301 Fixed in 3.1.7, 2.5.301 Patch available CNA
  • MessagePack (NuGet) Vendor— Affected before 2.5.301 Fixed in 2.5.301 Patch available GHSA-hv8m-jj95-wg3x
  • MessagePack (NuGet) Vendor— Affected 3.0.214-rc.1 to before 3.1.7 Fixed in 3.1.7 Patch available GHSA-hv8m-jj95-wg3x

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:messagepack:messagepack:*:*:*:*:*:c\#:*:*before 2.5.301; 3.0.3 to before 3.1.7VulnerableMessagePack-CSharp
  • cpe:2.3:a:messagepack:messagepack:*:*:*:*:*:c\#:*:* Versions before 2.5.301; 3.0.3 to before 3.1.7 Vulnerable ·MessagePack-CSharp

Remediation

  • Fix · CNA MessagePack-CSharp (MessagePack-CSharp) Fixed in 3.1.7, 2.5.301
  • Fix · GHSA-hv8m-jj95-wg3x MessagePack (NuGet) Fixed in 2.5.301 Advisory →
  • Fix · GHSA-hv8m-jj95-wg3x MessagePack (NuGet) Fixed in 3.1.7 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-48109
  2. 2026-10-03 Alias added: GHSA-hv8m-jj95-wg3x

References

Advisory 2

Other 1

  • TI-2026-35866 MessagePack-CSharp: MessagePackReader.Skip can recurse without enforcing maximum object graph depth CVSS 3.1HIGH 7.5
  • TI-2026-35873 MessagePack-CSharp: DynamicUnionResolver generated deserializers miss depth enforcement CVSS 4.0MEDIUM 6.3
  • TI-2026-35863 Out-of-bounds read in MessagePack-CSharp CVSS 4.0HIGH 8.2
  • TI-2020-04290 Untrusted data can lead to DoS attack in MessagePack for C# and Unity CVSS 3.1MEDIUM 6.5
  • TI-2026-35877 MessagePack-CSharp: Typeless deserialization type restrictions do not recurse into arrays or generic arguments CVSS 4.0MEDIUM 6.3
  • TI-2026-35876 MessagePack-CSharp: InterfaceLookupFormatter bypasses collision-resistant comparer settings CVSS 4.0MEDIUM 6.3
See all 12 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences