Chrome bug can take over accounts

Published August 5, 2026

Anthropic's Claude browser assistant can be tricked by a hidden message inside an email into stealing your login codes. An attacker can use that to take over your Slack, X, or Claude.ai account without you noticing.

Report priority
Medium
Targets
Claude in Chrome+3 more

How it works

  • An attacker emails the victim's Gmail with hidden instructions.
  • When the person asks Claude to summarize their inbox, Claude reads that email and runs the attacker's JavaScript inside the victim's own logged-in browser session, letting it check Gmail for incoming codes.

What to do

If you use the Claude in Chrome extension and let it read your email, avoid asking Claude in Chrome to summarize or act on unread emails from unknown senders, and watch for unexpected sign-in codes or password-reset emails from Slack, X, or Claude.ai. There is no version number to check since this is a behavior flaw, not a specific build.

Technical details

Affected software: Claude in Chrome, Slack, Claude.ai, Gmail

An attacker sends a booby-trapped email to the victim's Gmail inbox. The victim asks Claude in Chrome to summarize recent emails, and Claude follows hidden instructions in that message to run attacker-supplied JavaScript. The code requests a sign-in code from Slack for the victim's address, then reads the victim's Gmail to grab the code and hands it to the attacker, who signs in as the victim.

The flaw is an indirect prompt injection: text inside an email is interpreted by Claude as instructions rather than content, letting it invoke its javascript_tool inside the victim's authenticated session. Attacker JavaScript queried Gmail's Atom feed for unread message metadata to harvest Slack sign-in codes, X password-reset codes, and Claude.ai magic-link nonces, then completed each account's authentication flow. Researchers at Zenity Labs also found the payload delivered via a JavaScript package on a registry mimicking a legitimate CDN, which performed a harmless-looking action while running the theft in the background.

References

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