CVE-2026-41448: AdGuard Home Authentication Bypass via Path Traversal in Admin-Token Cookie

Synopsis

Authentication bypass in AdGuard Home allows unauthenticated remote attackers to gain full admin access by supplying a path traversal sequence in the Admin-Token cookie. The vulnerability exists specifically when AdGuard Home is started with the --glinet flag, and it stems from unsanitized string concatenation in the token file path construction inside the authglinet middleware. Successful exploitation gives the attacker complete administrative control over the AdGuard Home instance. A patched-image rebuild at version 0.107.77 is available on HarborGuard for environments running an affected version.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker must reach the AdGuard Home admin interface over the network; the vulnerable middleware processes unauthenticated HTTP requests exposed on the network.

• AuthenticationNot required

  No credentials are needed; the path traversal payload in the Admin-Token cookie bypasses authentication entirely before any credential check occurs.

• Victim interactionNot required

  No user interaction is required; the attacker sends a crafted HTTP request directly to the service without any victim involvement.

• Attack complexityDetail

  Base exploit conditions are reliable and condition-free (AC:L), though successful exploitation carries a specific precondition (AT:P): AdGuard Home must be running with the --glinet flag enabled.

Blast Radius

• Attacker gains full administrative control over the AdGuard Home instance, including the ability to read and modify all DNS filtering rules and configurations.
• Attacker can redirect DNS responses for all clients routed through the affected AdGuard Home server, enabling traffic interception or redirection.
• Attacker can disable ad and malware blocking rules, exposing downstream clients to previously filtered content.
• Service availability is lightly degraded (VA:L), meaning an attacker can partially disrupt DNS resolution for clients dependent on the instance.