The extension just became an agent backdoor. a malicious browser add-on called bragjack hijacked ai…
the extension just became an agent backdoor. a malicious browser add-on called bragjack hijacked ai agents across chrome, edge, comet, opera neon and claude, per october reporting, with chrome patched in v143.
the sidebar now needs its own security review.
Context
Verified event date: Forever Security researcher Gal Weizman disclosed BragJack on Sep 16, 2026, showing that a single ordinary browser extension could hijack the built-in AI agents of five browsers: Gemini Live in Chrome, Microsoft Edge, Opera Neon, Perplexity Comet and Claude in Chrome (Forever Security; BleepingComputer, Sep 19; Cloud Security Alliance, Sep 22).
The Cloud Security Alliance note says the extension needed only two permissions common among ad blockers; Forever Security says the flaws earned tens of thousands of dollars in bounties from Google, Anthropic, Microsoft, Perplexity and Opera.
The five affected products match the research. BragJack is a proof-of-concept technique demonstrated by researchers, so 'a malicious add-on hijacked agents' describes a demonstration, not a reported in-the-wild campaign in the sources read. The disclosure date is Sep 16, 2026, not 'october reporting', and the Chrome v143 patch was not seen in the sources read, so unsupported here, not refuted. in the excerpts read, though the researchers say bounties were paid by all five vendors. 'The sidebar now needs its own security review' is the author's.
'the extension just became an agent backdoor' is the author's opinion.
Related work
Watch next
- Check which fixes shipped, including any Chrome 143 patch.
Sources
- Forever Security: BragJack technical overviewforever.security
- Cloud Security Alliance: BragJack and the agentic browser monoculturelabs.cloudsecurityalliance.org
- Cloud Security Alliance: BragJack research note PDFlabs.cloudsecurityalliance.org
Provenance
The note above is reproduced unedited from the original post, first published on Threads on 11 October 2026 at 14:46 IST. Sources are the papers and datasets the note draws on.
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