CVE-2026-57578: 
C# vulnerability analysis and mitigation

CVE-2026-57578 is a missing authorization vulnerability in the DotVVM framework's AuthorizeActionFilter class, classified as Critical. The flaw affects the NuGet package DotVVM in versions prior to 4.2.11, versions greater than 4.3.0-preview01-final and prior to 4.3.15, and versions from 5.0.0-preview01-final through prior to 5.0.0-preview09-final. It was published on June 18, 2026, and reviewed in the GitHub Advisory Database on June 19, 2026. The vulnerability carries a CVSS v4 base score of 9.2 (Critical) (GitHub Advisory, DotVVM Advisory).

The root cause is classified as CWE-862 (Missing Authorization): the AuthorizeActionFilter class in DotVVM simply performs no authorization checks whatsoever — it is effectively a no-op. Any application relying on this class to enforce access control receives no protection, meaning any network-accessible action decorated with this filter is fully exposed without requiring authentication or elevated privileges. The attack vector is network-based with low complexity, though an "Attack Requirements: Present" condition is noted (the application must be using AuthorizeActionFilter specifically). No special hacking techniques are required; the filter's complete inaction is the vulnerability itself (GitHub Advisory, DotVVM Advisory).

All users of the AuthorizeActionFilter class are affected, as any actions or endpoints protected solely by this filter are completely unprotected. Successful exploitation allows unauthenticated remote attackers to access restricted functionality, read sensitive data, modify application state, and potentially disrupt availability — resulting in high confidentiality, integrity, and availability impact on the vulnerable system. The scope of impact depends on what actions the application intended to protect with the filter, which could range from sensitive data exposure to full administrative access (GitHub Advisory, DotVVM Advisory).

No exploit code, proof-of-concept, or in-the-wild exploitation has been publicly reported as of the advisory date. The vulnerability requires no authentication, no user interaction, and no special tools — any HTTP request to a protected endpoint is sufficient to bypass the non-functional filter. The advisory was published in June 2026 and no EPSS score or CISA KEV catalog listing is currently available for this CVE (DotVVM Advisory).

1. Reconnaissance: Identify web applications built with DotVVM (NuGet package) that are publicly accessible, particularly those using versions prior to 4.2.11, prior to 4.3.15, or prior to 5.0.0-preview09-final.
2. Identify protected endpoints: Review the application's source code (if available) or probe the application to identify endpoints or actions decorated with AuthorizeActionFilter that are intended to be restricted.
3. Send unauthenticated requests: Issue standard HTTP requests (e.g., via a browser or curl) directly to the protected endpoints without providing any authentication credentials or session tokens.
4. Access restricted functionality: Because AuthorizeActionFilter performs no authorization checks, the request is processed normally, granting the attacker full access to the protected resource or action — enabling data exfiltration, unauthorized data modification, or other privileged operations (DotVVM Advisory).

• Logs: Web server or application logs showing unauthenticated requests successfully accessing endpoints that should require authorization (e.g., admin panels, data management routes), with HTTP 200 responses where 401/403 would be expected.
• Network: Unusual or repeated access patterns to sensitive application endpoints from unknown or unexpected IP addresses without prior authentication flows (no login requests preceding access).
• Application Behavior: Unexpected data modifications, unauthorized record creation or deletion, or access to privileged application features without corresponding authenticated sessions in application audit logs.

Upgrade DotVVM to one of the patched versions: 4.2.11, 4.3.15, or 5.0.0-preview09-final. As an immediate workaround for those unable to upgrade, replace all uses of AuthorizeActionFilter with AuthorizeAttribute, which correctly implements the same interfaces and enforces authorization. The AuthorizeAttribute is deprecated for unrelated reasons, but the advisory explicitly endorses suppressing the deprecation warning when using it as an action filter in this context (DotVVM Advisory, GitHub Advisory).

The advisory was published by exyi (a DotVVM maintainer) on June 18, 2026, and reviewed in the GitHub Advisory Database on June 19, 2026. No significant broader media coverage, researcher commentary, or social media discussion has been identified at this time (DotVVM Advisory).