What is CVE-2026-48509?

CVE-2026-48509 is a critical-severity vulnerability in Messagepack, classified under Initialization of a Resource with an Insecure Default. CVSS score: 9.1/10. Published 2026-06-22.

How severe is CVE-2026-48509?

Critical severity. CVSS v3 base score is 9.1 out of 10.

RCE in Messagepack

CVE-2026-48509

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 Messa…

CVSS v3 metric

CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H.

Affected products

Messagepack
Messagepack-csharp — versions >= 3.1.7, < 3.1.7, < 2.5.301

Weakness classification (CWE)

CWE-1188 — Initialization of a Resource with an Insecure Default

References

security-advisories@github.com (x_refsource_CONFIRM, Mitigation, Vendor Advisory)

Frequently asked questions

What is CVE-2026-48509?: CVE-2026-48509 is a critical-severity vulnerability in Messagepack, classified under Initialization of a Resource with an Insecure Default. CVSS score: 9.1/10. Published 2026-06-22.
How severe is CVE-2026-48509?: Critical severity. CVSS v3 base score is 9.1 out of 10.