ShadowPrompt: Zero-Click Prompt Injection in Claude Chrome Extension — Any Website Could Silently Hijack the AI Assistant
The Hacker News·medium signal
Researchers disclosed ShadowPrompt, a vulnerability chaining an overly permissive origin allowlist (any *.claude.ai subdomain) with a DOM-based XSS in an Arkose Labs CAPTCHA component. An attacker's page embeds the vulnerable component in a hidden iframe, sends the XSS payload via postMessage, and the injected script fires prompts to the extension — zero clicks, zero permission prompts. Could steal access tokens, exfiltrate conversation history, and perform actions on behalf of victims. Anthropic patched in extension v1.0.41 with strict origin matching.