Claude Dispatch Flaw Lets Malicious Browser Extensions Run Code on Connected Computers

A flaw in Anthropic’s Claude Dispatch let a malicious browser extension run commands on a computer via Claude Desktop. That computer could even be a different machine signed into the same Claude account.

Researcher Gal Weizman of Forever Security named the technique ThisBash and published the findings on November 4, 2026. Anthropic plans to retire Dispatch, but the design behind it still lives in other Claude features.

Dispatch lets a person send a task from a phone to Claude Desktop, an AI agent that can work with local files, apps, and commands. Anthropic’s help page says the feature is in limited beta and is closed to new users. The same page warns that a manipulated instruction could trigger actions that are hard to undo.

The researchers found no flaw in the phone-to-desktop link itself. The trouble started when the same workflow was reached from claude.ai in a browser, where an extension can run alongside the page.

Claude Dispatch Vulnerability

Claude Desktop is an Electron app. That means it is built from the same web interface and API as claude.ai. The web version only hid the Dispatch link. It never blocked access to it. Once someone copied the page address from the desktop app, any logged-in browser tab could open Dispatch and send requests.

An extension with permission to run scripts on claude.ai could do the same through the user’s own cookies. In the proof of concept, the script opened Dispatch in a tiny 200 by 200 pixel background window. It then asked the API for the session ID of the user’s desktop agent. This was the only visible trace on screen.

Claude first hesitated when asked to install an unknown npm package. The script read each reply and sent a follow-up in the user’s voice. Forever Security calls this prompt forcing. In normal prompt injection, hostile text hides inside a page or file that the model reads, and the attacker gets one try. In prompt forcing, the attacker controls the whole chat and can rephrase, insist and try new angles until the model gives in.

Four written prompts were enough. A short loop also clicked any “Allow” button once per second, so no human had to approve anything. The package then ran and opened Calculator. The team noted that the same step could have copied files, added SSH keys or planted a backdoor.

Dispatch is built to link devices, so the browser and the desktop do not need to be on one computer. Picture an employee who signs into a personal Claude account on a work laptop. A bad extension in their home browser could then send orders to that work laptop. It would run next to source code and cloud keys. The researchers said they have seen personal accounts with cross-device Dispatch turned on at corporate endpoints.

Extensions are common enough to make this a real path. LayerX found that 99% of enterprise users in its sample had at least one extension, and 53% had extensions with high or critical permissions. Forever Security’s earlier MaXSS and Spyder research showed how flaws in two popular Chrome extensions, with over 10 million installs between them, could let websites act across other sites. A bad extension can come from a rogue install, a hijacked update or a bug in a trusted tool.

A malicious extension can already read pages, steal data and act through logged-in sessions. That is serious. But it normally stays inside the browser. ThisBash crossed that line. Permission to talk to a website became permission to run commands on the computer.

The requests also looked real. They came from a real session and a real account, with permissions the user had granted. That proved who was logged in. It did not prove the user wanted a command to run. The researchers put it this way: a web session alone is not proof that the user approved an action on their machine.

Researchers have shown extensions steering AI tools several times this year. Cyber Security News covered BragJack, where a single extension took over the built-in assistants of five major browsers. That story shows the problem goes well beyond one vendor. Any AI tool that trusts the page it sits in can be steered by code running in that page.

Weizman reported the issue to Anthropic on May 14, 2026. Anthropic confirmed it was valid on May 19 but closed the report as a duplicate of a problem it had already found. On October 13, the company said Dispatch would be retired, with a target of the end of October 2026. That date has now passed, and I could not confirm from public sources that the feature is fully gone.

The wider concern is that Claude Code Remote Control and Cowork sessions let the web drive a local agent by design. The researchers say extensions can repeat the same trick there and plan a follow-up post. Taking away one feature does not remove the trust gap underneath.

Start with a list of the AI agents on your endpoints and the accounts they use. Check whether those accounts sit under company single sign-on. Turn off cross-device remote control where there is no business need, and review how devices are paired and removed.

Treat extensions like any other software. Limit who can install them, review their permissions and watch for updates that ask for more. Approval prompts should be something the requesting component cannot click for itself. Teams should also watch for odd package installs, config changes and credential access linked to agent activity.

Anthropic recently added a beta EDR monitoring option for Claude Cowork on Team and Enterprise plans, which can help with that last step. The simplest habit is also the strongest. Keep personal AI accounts off work devices, and keep work accounts out of personal browsers. ThisBash shows why that line matters.

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