MessagePack-CSharp MessagePack for C# up to 2.5.300/3.1.6 Compressed Data data amplification

Summaryinfo

A vulnerability described as problematic has been identified in MessagePack-CSharp MessagePack for C# up to 2.5.300/3.1.6. Affected by this issue is some unknown functionality of the component Compressed Data Handler. The manipulation results in data amplification. This vulnerability is identified as CVE-2026-48510. The attack can be executed remotely. There is not any exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as problematic, was found in MessagePack-CSharp MessagePack for C# up to 2.5.300/3.1.6. Affected is an unknown code block of the component Compressed Data Handler. The manipulation with an unknown input leads to a data amplification vulnerability. CWE is classifying the issue as CWE-409. The product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output. This is going to have an impact on availability. CVE summarizes:

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, when MessagePack-CSharp decompresses Lz4Block or Lz4BlockArray payloads, it reads declared uncompressed lengths from the wire and allocates output buffers based on those lengths before validating that the compressed data is valid or that the declared expansion is reasonable. A small payload can claim a very large uncompressed length and force a large allocation before LZ4 decoding begins. This vulnerability is fixed in 2.5.301 and 3.1.7.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-48510 since 05/21/2026. The exploitability is told to be difficult. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. The technical details are unknown and an exploit is not available. This vulnerability is assigned to T1499 by the MITRE ATT&CK project.

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

CPE 2.3info

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CPE 2.2info

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