MessagePack-CSharp MessagePack for C# up to 2.5.300/3.1.6 Decoder input validation

Summaryinfo

A vulnerability, which was classified as critical, was found in MessagePack-CSharp MessagePack for C# up to 2.5.300/3.1.6. The impacted element is an unknown function of the component Decoder. Executing a manipulation can lead to input validation. This vulnerability appears as CVE-2026-48109. The attack may be performed from remote. There is no available exploit. You should upgrade the affected component.

Detailsinfo

A vulnerability classified as critical was found in MessagePack-CSharp MessagePack for C# up to 2.5.300/3.1.6. This vulnerability affects some unknown functionality of the component Decoder. The manipulation with an unknown input leads to a input validation vulnerability. The CWE definition for the vulnerability is CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-48109 since 05/20/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are neither technical details nor an exploit publicly available.

Upgrading to version 2.5.301 or 3.1.7 eliminates this vulnerability.

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Productinfo

Vendor

• MessagePack-CSharp

Name

• MessagePack for C#

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5.300
• 3.1.0
• 3.1.1
• 3.1.2
• 3.1.3
• 3.1.4
• 3.1.5
• 3.1.6

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CPE 2.2info

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