MessagePack-CSharp MessagePack for C# up to 2.5.300/3.1.6 MessagePackInputFormatter insecure default initialization of resource

Summaryinfo

A vulnerability classified as problematic has been found in MessagePack-CSharp MessagePack for C# up to 2.5.300/3.1.6. This affects the function MessagePackInputFormatter. This manipulation causes insecure default initialization of resource. This vulnerability is tracked as CVE-2026-48509. The attack is possible to be carried out remotely. No exploit exists. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability has been found in MessagePack-CSharp MessagePack for C# up to 2.5.300/3.1.6 and classified as problematic. Affected by this vulnerability is the function MessagePackInputFormatter. The manipulation with an unknown input leads to a insecure default initialization of resource vulnerability. The CWE definition for the vulnerability is CWE-1188. The product initializes or sets a resource with a default that is intended to be changed by the administrator, but the default is not secure. As an impact it is known to affect integrity, and availability. The summary by CVE is:

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, the parameterless MessagePackInputFormatter() constructor uses default serializer options, which resolve to MessagePackSerializerOptions.Standard with MessagePackSecurity.TrustedData. The formatter is designed for ASP.NET Core MVC request bodies, which commonly cross an HTTP trust boundary. This insecure default can expose applications to denial-of-service attacks that MessagePackSecurity.UntrustedData is intended to mitigate, such as hash-collision attacks against dictionary-like model properties. This vulnerability is fixed in 2.5.301 and 3.1.7.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-48509 since 05/21/2026. The exploitation appears to be difficult. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 2.5.301 or 3.1.7 eliminates this vulnerability.

Be aware that VulDB is the high quality source for vulnerability data.

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

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Be aware that VulDB is the high quality source for vulnerability data.

Discussion