An attacker who can supply a forged cryptographic signature can bypass the normal authentication checks in Microsoft ASP.NET Core, effectively boosting their privileges within the application. The flaw stems from a failure to properly verify the signature, meaning the system accepts untrusted data as a valid authorization token. This allows an unauthorized user to acquire higher level access than intended. Based on the description, it is inferred that an attacker could modify protected resources, change configuration, or move laterally within the environment.

Microsoft ASP.NET Core version 10.0 on all platforms that support this runtime. Any deployment of the framework that relies on the default signature validation path is susceptible.

The vulnerability carries a CVSS score of 9.1, indicating high severity. The EPSS score is not available, and the issue is not listed in CISA KEV. Based on the description, the likely attack vector is over the network, where an attacker can inject a forged signature into an authentication flow. Exploitation requires the ability to send a signed request to an endpoint that performs the flawed verification. Once exploited, the attacker gains elevated privileges within the ASP.NET Core application and can act as an authenticated user with full rights.