{
 "public_id": "AIR-2026-0080",
 "incident_id": "2026-03-anthropic-claude-chrome-shadowprompt",
 "date_disclosed": "2026-03-26",
 "date_occurred": null,
 "title": "ShadowPrompt: any website could hijack Anthropic's Claude Chrome extension via an over-broad origin allowlist",
 "class": "responsible_disclosure",
 "attack_surface": "browser_agent",
 "initial_vector": "cross_origin_message_injection",
 "agent_capability_abused": [
  "extension_message_passing",
  "browser_automation",
  "browser_control",
  "authenticated_session_reuse",
  "email_send",
  "file_read"
 ],
 "target_product": "Claude Chrome extension, versions below 1.0.41",
 "target_vendor": "Anthropic",
 "autonomy_level": "semi_autonomous",
 "impact_realized": false,
 "impact_type": [
  "agent_hijack",
  "data_exfiltration",
  "credential_theft",
  "unauthorized_actions"
 ],
 "blast_radius": "All Claude Chrome extension users below 1.0.41",
 "cve": [],
 "taxonomy": {
  "owasp_asi": [
   "ASI01",
   "ASI04",
   "ASI03"
  ],
  "mitre_atlas": [],
  "labels": [
   "xss",
   "origin_validation",
   "browser_agent",
   "zero_click",
   "xss_chain",
   "origin_allowlist_wildcard",
   "invisible_iframe",
   "supply_chain_third_party_captcha"
  ]
 },
 "defense_present": "Origin allowlist matching *.claude.ai",
 "defense_bypassed": true,
 "fix_shipped": "Patch deployed 2026-01-15; extension now requires exactly https://claude.ai",
 "primary_sources": [
  "https://www.koi.ai/blog/shadowprompt-how-any-website-could-have-hijacked-anthropic-claude-chrome-extension"
 ],
 "verified_quote": "With JavaScript execution on a-cdn.claude.ai, the final step writes itself. The injected script sends a message to the Claude extension using chrome.runtime.sendMessage",
 "confidence": "high",
 "notes": "Author Oren Yomtov. Chained a wildcard origin allowlist with a DOM XSS in an Arkose Labs CAPTCHA component on a-cdn.claude.ai. Disclosed 2025-12-26, confirmed by Anthropic within 24 hours. No CVE listed in the post. | Merged from duplicate id `2026-03-koi-shadowprompt-claude-chrome`. Also reported as: 'ShadowPrompt: zero-click prompt injection chain hijacks Anthropic's Claude for Chrome extension from any website'.",
 "risk_category": "security_fraud",
 "risk_secondary": [
  "privacy",
  "product_misuse"
 ],
 "risk_subcategory": "Supply Chain Compromise",
 "risk_sub_secondary": [
  "Credential & Secret Theft"
 ],
 "ai_entity": "generative",
 "agency": "agent_acted",
 "agency_debatable": false,
 "agency_reason": "any website could drive the extension's browser automation and email send",
 "vector_family": "other",
 "vector_detail": "cross_origin_message_injection",
 "guardrail_kind": [
  "permission_scope"
 ],
 "guardrail_outcome": "silent",
 "xrefs": {
  "aiid": [],
  "atlas": [],
  "cve": [],
  "ghsa": []
 },
 "primary_asi": "ASI01",
 "agent_framework": "unknown",
 "model_provider": "anthropic",
 "model_name": "",
 "detection_mechanism": "external_researcher",
 "tool_access": "unknown",
 "financial_loss_band": "unknown",
 "eai_category": "supply_chain_vulnerabilities",
 "eai_domain": "tool_misuse",
 "eai_secondary": [
  "unsafe_actuation",
  "credential_theft",
  "data_exfiltration_channels"
 ],
 "eai_reason": "subcategory: Supply Chain Compromise",
 "asi_curated": [
  "ASI01"
 ],
 "asi_scope": "in_scope",
 "asi_provenance": "curated_plus_rule",
 "asi_reason": "curated: ASI01 | added ASI04 (eai_category=supply_chain_vulnerabilities), ASI03 (signal=identity)",
 "submitted_by": "EAI Internal"
}