Insecure Default Initialization of Resource Affecting messagepack.aspnetcoremvcformatter package, versions [,2.5.301)[3.0,3.1.7)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-DOTNET-MESSAGEPACKASPNETCOREMVCFORMATTER-17660974
- published28 Jun 2026
- disclosed25 Jun 2026
- creditAArnott
Introduced: 25 Jun 2026
CVE-2026-48509 (opens in a new tab)How to fix?
Upgrade MessagePack.AspNetCoreMvcFormatter to version 2.5.301, 3.1.7 or higher.
Overview
Affected versions of this package are vulnerable to Insecure Default Initialization of Resource due to the parameterless MessagePackInputFormatter constructor using insecure default serializer options, which resolve to a trusted data security posture. An attacker can cause denial of service or degrade application performance by sending specially crafted HTTP request bodies with colliding keys to exploit hash-based collections during model binding. This is only exploitable if the formatter is registered using the parameterless constructor without explicitly configuring untrusted-data options.
Workaround
This vulnerability can be mitigated by registering the formatter with explicit untrusted-data options and applying normal HTTP request-size limits and model validation.