CVE-2026-48509
Published: 22 June 2026
Summary
CVE-2026-48509 is a medium-severity Initialization of a Resource with an Insecure Default (CWE-1188) vulnerability in Messagepack Messagepack. Its CVSS base score is 6.3 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 14.6th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-38387
Vulnerability details
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Insecure default in public-facing ASP.NET Core deserializer directly enables DoS exploitation over HTTP trust boundary.
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Requires documented secure initialization practices and avoidance of insecure defaults in configuration baselines.
Reviewing and updating baseline when components are installed or upgraded prevents initialization with insecure defaults.
Requiring explicit configuration to minimal functionality overrides insecure defaults that would otherwise enable excess capabilities.
Tailoring replaces or augments insecure default initializations with system-specific values and compensating controls before deployment.
Central configuration overrides or replaces insecure default initializations that would otherwise be left unchanged on each system.
SCRM practices during acquisition and configuration management address insecure default initializations shipped by vendors.
Scans detect resources initialized with insecure defaults that create exploitable conditions.
Instruction on secure initialization of security controls prevents leaving resources with insecure defaults after installation.