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

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Summary

CVECVE-2026-48109
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-22 22:16:46 UTC
Updated2026-06-23 17:25:43 UTC
DescriptionMessagePack 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.

Risk And Classification

Primary CVSS: v3.1 8.2 HIGH from [email protected]

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

EPSS: 0.002960000 probability, percentile 0.211570000 (date 2026-06-24)

Problem Types: CWE-20 | CWE-20 CWE-20: Improper Input Validation

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary8.2HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
3.1CNADECLARED8.2HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
High

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Messagepack Messagepack All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA MessagePack-CSharp MessagePack-CSharp affected >= 3.1.7, < 3.1.7 Not specified
CNA MessagePack-CSharp MessagePack-CSharp affected < 2.5.301 Not specified

References

ReferenceSourceLinkTags
github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHS... [email protected] github.com Mitigation, Vendor Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis
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