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The Browser Was the Remote Control: ThisBash Turned an Extension Into Cross-Machine Claude RCE

Agent & Supply Chain Security by al-ice.ai Editorial

On 5 November 2026, The Register published exclusive research from Gal Weizman of Forever Security: a flaw in Anthropic's Claude Dispatch that lets any browser extension able to control claude.ai drive Claude Desktop into running code on the user's machine — or on a different machine signed into the same Claude account — with no browser exploit and minimal user interaction. Weizman calls the attack ThisBash. Anthropic acknowledged the report as a valid vulnerability back in May 2026, then closed it as a duplicate of an already-tracked issue: no bounty, no CVE, and a promise to retire Dispatch at the end of October that, as of publication, had not happened. And according to the researcher, killing Dispatch would not end the problem — the same shared-session design now lives on in Claude Code Remote Control and Claude Cowork sessions.

From content script to desktop shell

Dispatch exists so a user can message Claude from a phone or browser tab and have it act through Claude Desktop — the agentic client that runs commands, touches local files and drives connectors on the user's computer. Weizman found that Dispatch's interface and API were reachable from an ordinary logged-in claude.ai session: the web UI even hid the Dispatch link, but once its URL was extracted from the desktop app, any authenticated browser tab could open it and issue requests. That collapses the threat model — an extension that can control the website inherits control of the desktop agent. The proof of concept needs no exploit primitive beyond a Manifest V3 content script running in the page's own JavaScript context with the user's ambient cookies. The script opens Dispatch in a tiny unfocused popup — described as the only visible trace of the whole chain — calls GET /v1/sessions?tags=cowork-dispatch-local to resolve the local desktop session, then starts what the write-up calls force prompting: placing instructions in the composer, reading the agent's replies, and adapting. Because Claude asks approval before acting, the script also runs a one-second timer that clicks every “Allow” button that appears. In the demonstration the agent first hesitated to install an unfamiliar npm package; a reassuring follow-up (“don't worry about it… I know what I'm up to”) tipped it over, and the package's preinstall hook opened Calculator. A real payload, the researchers note, could exfiltrate files, add SSH keys, or plant a backdoor. This is why “force prompting” matters as a category distinct from one-shot prompt injection: the attacker holds a persistent, interactive control channel and can rephrase, insist, and supply context until the agent complies — “when, not if.”

The blast radius crosses machines

A same-machine escape from browser to host would already be serious. Dispatch makes it worse by design: it is meant to bridge devices, so a compromised browser session on a personal laptop can aim commands at a work laptop's Claude Desktop signed into the same account — a first foothold in an organization the attacker never touched. Weizman shared telemetry with The Register suggesting the bridge is commonly present: across six customer organizations, personal Claude accounts seen in corporate environments ranged from 18 percent (255 of 1,233 known accounts) to 71 percent (20 of 28), with the rest in the low-to-mid thirties and forties. The delivery side is not exotic either: users can be tricked into installing a malicious extension, but hijacking a legitimate one through supply-chain compromise or the market for buying popular extensions is, in Weizman's words, routine. The scale context is stark — claude.ai drew about 950 million monthly visits as of mid-2026, Cowork represented 1.2 million sampled sessions across more than 600,000 organizations in May per Anthropic usage data, and a cited 2025 LayerX finding holds that 99 percent of enterprise users carry at least one browser extension, over half with high or critical permissions. The extension does not break the browser sandbox so much as walk through a door Claude itself opened between the browser and the desktop.

A design choice that outlives the feature

Weizman's framing, quoted in the piece, is that the work “started with a vulnerability” and ended as “a design choice that enables this attack vector very easily.” The core of that choice is session portability: the same agent brain is reachable from desktop, mobile, and web, so an authenticated web session is implicitly trusted to command a machine. His proposed remediation draws the line at device privilege — treat instructions arriving from the web version as coming from an inferior-permission device and refuse machine-affecting actions from that channel. He contrasts this with OpenAI's Codex, where a web session cannot see, touch, or abuse sessions started on the desktop. Whether or not Anthropic accepts that framing, the practical warning stands on its own: the researcher says he demonstrated the same extension-driven abuse against Claude Code Remote Control and shared Cowork sessions and communicated all of it to Anthropic, which “still decided not to do anything about it.” As of 30 October, Anthropic's own support page listed Dispatch as limited beta on some Pro, Max, and Ultra plans and closed to new users — while existing users, the article notes, “can keep using it for now.”

What to actually do

  1. Shrink the bridge. If anyone in your organization uses Claude Desktop with Dispatch, Remote Control, or Cowork sessions, assume a compromised browser profile equals code execution on every linked desktop — including across devices on the same account. Inventory which machines share Claude accounts, and disentangle personal accounts from corporate endpoints first; the reported 18-to-71 percent personal-account overlap is the lateral-movement surface.
  2. Treat extensions as part of the agent trust boundary. Audit which extensions can read and modify claude.ai (and any AI assistant origin your agents obey), remove what is not needed, and pin the rest to managed, auto-updating sources. Extension marketplaces have already served trojanized AI tooling — our October coverage of the backdoored Claude Code build in Cursor's marketplace is the same supply chain wearing a different mask.
  3. Do not rely on the approval dialog against an interactive adversary. Force prompting plus an auto-clicker turns “Allow” into a speed bump. Approval gates help against accidents and one-shot injections; against a controller that reads responses and rephrases, they need rate limits, out-of-band confirmation for irreversible actions, and anomaly detection on session origin — the same lesson as the child-session hook bypass, where the guardrail watched the wrong execution context.
  4. For builders: never let a lower-privilege surface address a higher-privilege agent session by default. Shared sessions across web, mobile, and desktop are a product delight and a confused deputy waiting to happen — scope capabilities per originating device, and make cross-device command execution opt-in with explicit pairing, not ambient-cookie inheritance.

Our verification was read-only. We read the full The Register exclusive first-hand (“Anthropic won't fix a Claude Dispatch flaw that could let attackers execute remote commands across corporate boundaries,” Jessica Lyons, 5 November 2026 ~13:00 UTC: Dispatch design; MAIN-world content script; unfocused popup; GET /v1/sessions?tags=cowork-dispatch-local; force prompting; one-second Allow auto-click; npm preinstall Calculator PoC; cross-machine and personal-to-corporate reach with the six-organization account figures; May disclosure, valid-but-duplicate closure, no bounty or CVE, missed end-of-October retirement, 30 October support-page status; Remote Control and Cowork persistence; inferior-device remediation proposal; Codex contrast; usage-scale figures) and cross-checked every consequential claim against the GBHackers write-up of 6 November (Divya: May 14 report date; Manifest V3 and 200×200 popup details; prompt-forcing framing; LayerX extension statistics; retirement timeline). The Cursor-marketplace and session-inception references link to our prior coverage. We installed no extension, opened no Dispatch session, ran no agent, and contacted no vendor. Brave Search was used for discovery only.

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