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TI-2026-35869 Aliases CVE-2026-48509GHSA-2f33-pr97-265q

MessagePack-CSharp: ASP.NET Core MessagePackInputFormatter defaults to TrustedData for HTTP request bodies

Priority LOW 28CWE-1188Published · Updated

Key facts

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

Attack profile from CVSS 4.0 · 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, 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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00416 36th 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
No
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-CSharp3.0 to before 3.1.7; before 2.5.3013.1.7, 2.5.301Patch availableCNA
—MessagePack (NuGet)before 2.5.3012.5.301Patch availableGHSA-2f33-pr97-265q
—MessagePack (NuGet)3.0 to before 3.1.73.1.7Patch availableGHSA-2f33-pr97-265q
  • MessagePack-CSharp VendorMessagePack-CSharp Affected 3.0 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-2f33-pr97-265q
  • MessagePack (NuGet) Vendor— Affected 3.0 to before 3.1.7 Fixed in 3.1.7 Patch available GHSA-2f33-pr97-265q

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-2f33-pr97-265q MessagePack (NuGet) Fixed in 2.5.301 Advisory →
  • Fix · GHSA-2f33-pr97-265q MessagePack (NuGet) Fixed in 3.1.7 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-48509
  2. 2026-10-03 Alias added: GHSA-2f33-pr97-265q

References

Advisory 2

Other 1

  • TI-2026-35549 MessagePack-CSharp: LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad input CVSS 3.1HIGH 8.2
  • 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
See all 12 →

Sources

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