Claude Extension Flaw Enabled Zero-Click XSS Prompt Injection via Any Website
ID: d90e29ba-d09d-5e33-8ded-255fea2334d1
STIX ID: report--d90e29ba-d09d-5e33-8ded-255fea2334d1
Feed Name: The Hacker News
Researchers disclosed a vulnerability called "ShadowPrompt" in Anthropic's Claude Chrome extension where an overly permissive origin allowlist plus a DOM-based XSS in an Arkose Labs CAPTCHA on a-cdn.claude.ai allowed any website to silently inject prompts into the assistant without user interaction; successful exploitation could leak access tokens, expose conversation history, or let attackers act on users' behalf. Anthropic patched the extension (v1.0.41) to enforce exact-origin checks after responsible disclosure on December 27, 2025, and Arkose Labs fixed the XSS on February 19, 2026.
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