A critical authentication bypass in AdGuard Home allows unauthenticated attackers to gain full administrative access by exploiting a flaw in HTTP/2 protocol handling.

The vulnerability exists in the way AdGuard Home handles HTTP/1.1 requests that upgrade to HTTP/2 cleartext (h2c). The resulting connection bypasses the authentication middleware, allowing all subsequent HTTP/2 requests on that connection to be treated as fully authenticated without any credentials.

Attackers can gain complete control over network-wide ad-blocking and DNS settings, enabling them to redirect traffic to malicious sites or disable security protections. The CVSS score of 9.8 reflects the high severity of losing administrative control over a central network security component.

Immediate Action: Update AdGuard Home to version 0.107.73 or later to resolve the authentication middleware flaw.

Proactive Monitoring: Check logs for HTTP/1.1 to h2c upgrade requests and review DNS configuration history for unauthorized changes.

Compensating Controls: Disable HTTP/2 cleartext support if possible, or use a reverse proxy that properly handles authentication before passing traffic to the AdGuard Home service.

Public Exploit Available: false

Immediate patching is required to prevent unauthorized administrative access. Organizations and home users should ensure their AdGuard Home instances are updated to version 0.107.73 and should avoid exposing the management interface to the public internet.