{
 "public_id": "AIR-2026-0161",
 "incident_id": "2026-07-anthropic-claude-memory-heist",
 "date_disclosed": "2026-07-15",
 "date_occurred": null,
 "title": "The Memory Heist: chaining web_fetch link-following letter by letter to spell out and exfiltrate a user's Claude memories",
 "class": "responsible_disclosure",
 "attack_surface": "consumer_chatbot",
 "initial_vector": "malicious_website_with_user_agent_cloaking",
 "agent_capability_abused": [
  "web_fetch",
  "link_following",
  "long_term_memory_read"
 ],
 "target_product": "Claude.ai (memory + web_fetch)",
 "target_vendor": "Anthropic",
 "autonomy_level": "assistant",
 "impact_realized": false,
 "impact_type": [
  "data_exfiltration"
 ],
 "blast_radius": "Claude.ai users with memory enabled who ask about an SEO-poisoned topic",
 "cve": [],
 "taxonomy": {
  "owasp_asi": [
   "ASI01",
   "ASI04",
   "ASI06",
   "ASI02"
  ],
  "mitre_atlas": [],
  "labels": [
   "url_allowlist_bypass",
   "letter_by_letter_exfil",
   "cloaking",
   "memory_exfil",
   "seo_poisoning"
  ]
 },
 "defense_present": "web_fetch URL restriction: URLs must come from the user message, web_search results, or a previous web_fetch result",
 "defense_bypassed": true,
 "fix_shipped": "Anthropic disabled web_fetch's ability to follow links found in fetched page content",
 "primary_sources": [
  "https://www.ayush.digital/blog/the-memory-heist"
 ],
 "verified_quote": "The URL being fetched must either be specified directly in the user message, be specified directly in the results of a `web_search` query, or be linked in the content of a previous `web_fetch` result.",
 "confidence": "high",
 "notes": "Independent researcher (Ayush, ayush.digital), surfaced via Simon Willison's prompt-injection and exfiltration-attacks tags. The bypass is elegant: rather than constructing one URL with the secret in it, the attacker's site serves 26 alphabetical links and Claude walks them letter by letter, spelling the secret across a sequence of allowed fetches. Site cloaks by user-agent so a human visitor sees benign content. Disclosed via HackerOne; Anthropic said it had identified the issue internally and awarded no bounty. Researcher's noted escalation: SEO-optimize a page about a news event and any user asking about it is caught.",
 "risk_category": "privacy",
 "risk_secondary": [],
 "risk_subcategory": "Data Exfiltration via Context",
 "risk_sub_secondary": [],
 "ai_entity": "generative",
 "agency": "agent_acted",
 "agency_debatable": false,
 "agency_reason": "Claude followed the attacker's links letter by letter to spell out memories",
 "vector_family": "malicious_component",
 "vector_detail": "malicious_website_with_user_agent_cloaking",
 "guardrail_kind": [
  "unknown"
 ],
 "guardrail_outcome": "silent",
 "xrefs": {
  "aiid": [],
  "atlas": [],
  "cve": [],
  "ghsa": []
 },
 "primary_asi": "ASI01",
 "agent_framework": "unknown",
 "model_provider": "anthropic",
 "model_name": "",
 "detection_mechanism": "unknown",
 "tool_access": "unknown",
 "financial_loss_band": "unknown",
 "eai_category": "data_exfiltration_channels",
 "eai_domain": "privacy",
 "eai_secondary": [],
 "eai_reason": "subcategory: Data Exfiltration via Context",
 "asi_curated": [
  "ASI01"
 ],
 "asi_scope": "in_scope",
 "asi_provenance": "curated_plus_rule",
 "asi_reason": "curated: ASI01 | added ASI04 (vector_family=malicious_component), ASI06 (signal=memory), ASI02 (impact=tool_misuse)",
 "submitted_by": "EAI Internal"
}