Description

A critical security vulnerability has been discovered in AdGuard Home, a widely used network-level ad and tracker blocking solution. The flaw, tracked as CVE-2026-32136, has received a 9.8 (Critical) score on the Common Vulnerability Scoring System scale. This vulnerability allows remote attackers to bypass the platform’s authentication mechanism. If exploited, threat actors could gain full administrative access to the affected system without providing valid login credentials, potentially compromising the security and configuration of the network environment. The issue was discovered and responsibly disclosed by security researcher mandreko. After receiving the report, the AdGuard development team confirmed the vulnerability and quickly coordinated disclosure with public vulnerability databases. To protect users from potential exploitation, the developers released a security update (version 0.107.73) as an emergency hotfix. This rapid response aimed to mitigate the risk before attackers could actively exploit the flaw on a large scale. The vulnerability originates from how older versions of AdGuard Home process certain connection upgrade requests. An attacker can send a crafted HTTP/1.1 request that asks the server to upgrade the connection to HTTP/2 Cleartext (h2c). Once the server accepts the upgrade, the connection is forwarded to an internal component that does not enforce authentication checks. Because of this design weakness, all further requests sent through that channel are treated as authenticated, enabling attackers to perform administrative actions on the system.