Forever Security uses one extension to hijack five browsers' built-in agents, earning $20,000 in bounties and 2 CVEs
BragJack: How We Hijacked Top 5 Browsers' Internal Agents With Just One Single Extension
Forever Security's research team disclosed the BragJack attack, using a single ordinary Chromium extension to simultaneously break into five browsers' built-in agents—Gemini Live in Chrome, Perplexity Comet, Microsoft Edge Actions, Opera Neon, and Claude in Chrome—earning a total of $20,000 in bounties and obtaining CVE-2026-0628 and CVE-2026-55945. The core of the attack is Prompt Forcing, using the declarativeNetRequest permission to weaken security response headers like CSP and redirect JavaScript resources, thereby executing code in a privileged context and then directly issuing commands to the agent. Achievable effects include reading local files and browsing history, obtaining browser profile information, taking screenshots of tabs, and in the Gemini Live scenario, accessing the camera and microphone.
The research team used a single ordinary extension to simultaneously break into five browsers' built-in agents, and provided each vendor's fix status and bounty results, which can serve as a reference for browser and agent developers to check against.