CVE-2026-45591

A flaw was found in ASP.NET Core SignalR and Blazor Server. A remote attacker could send a specially crafted MessagePack payload containing deeply nested arrays that trigger excessive recursion and cause a stack overflow. This issue may result in application termination and a denial of service condition

This vulnerability affects the MessagePack hub protocol implementation used by ASP.NET Core SignalR and Blazor Server. Red Hat Product Security has assessed this issue as an Important severity vulnerability.

The flaw occurs when processing deeply nested MessagePack arrays supplied by a remote attacker. Insufficient validation of message nesting depth may cause excessive recursion and trigger a stack overflow condition during message processing.

Successful exploitation could allow an unauthenticated remote attacker to cause the affected application or service to terminate unexpectedly, resulting in a denial of service condition.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Red Hat is not aware of a practical temporary workaround that fully mitigates this issue or meets Red Hat Product Security's standards for usability, deployment, applicability, or stability. Customers are advised to apply the relevant security updates when they become available.