{
 "public_id": "AIR-2025-0179",
 "incident_id": "2025-11-anthropic-claude-for-excel-cellshock",
 "date_disclosed": "2025-11-24",
 "date_occurred": null,
 "title": "CellShock: Claude for Excel coerced into writing IMAGE() formulas that exfiltrate spreadsheet financials",
 "class": "responsible_disclosure",
 "attack_surface": "enterprise_assistant",
 "initial_vector": "indirect_prompt_injection_spreadsheet_hidden_text",
 "agent_capability_abused": [
  "spreadsheet_write",
  "formula_generation",
  "external_network_request_via_formula"
 ],
 "target_product": "Claude for Excel (beta)",
 "target_vendor": "Anthropic",
 "autonomy_level": "assistant",
 "impact_realized": false,
 "impact_type": [
  "data_exfiltration"
 ],
 "blast_radius": "Claude for Excel beta users importing untrusted spreadsheet data",
 "cve": [],
 "taxonomy": {
  "owasp_asi": [
   "ASI01",
   "ASI02"
  ],
  "mitre_atlas": [],
  "labels": [
   "indirect_prompt_injection",
   "formula_injection",
   "image_formula_exfil",
   "hidden_text",
   "evidence_destruction"
  ]
 },
 "defense_present": "warning modal before applying edits; Claude Opus 4.5 injection resistance",
 "defense_bypassed": true,
 "fix_shipped": "partial: improved warning modal + model upgrade; modal does not always trigger and invisible Unicode bypasses it",
 "primary_sources": [
  "https://www.promptarmor.com/resources/cellshock-claude-ai-is-excel-lent-at-stealing-data"
 ],
 "verified_quote": "Claude for Excel can be coerced by a prompt injection hidden in an untrusted data source to output unsafe formulas that exfiltrate data from the user's file to an attacker.",
 "confidence": "high",
 "notes": "PromptArmor. Injection hidden as blue-on-blue text in an imported sheet. Excel's IMAGE() formula fetches a URL, so appending stolen cell data to the URL leaks it to the attacker's server logs. Tested on Private Beta 11/18 and re-tested on Public Beta 11/24 after mitigations; year inferred as 2025 from the Claude Opus 4.5 / Claude for Excel beta timeline - treat the exact day as approximate. PromptArmor also observed that 'Claude inadvertently covered the attacker's tracks for them' by overwriting the malicious formula with a chart.",
 "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 wrote IMAGE() formulas that fetched attacker URLs with the data",
 "vector_family": "indirect_prompt_injection",
 "vector_detail": "indirect_prompt_injection_spreadsheet_hidden_text",
 "guardrail_kind": [
  "unknown"
 ],
 "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": "data_exfiltration_channels",
 "eai_domain": "privacy",
 "eai_secondary": [
  "confused_deputy"
 ],
 "eai_reason": "subcategory: Data Exfiltration via Context",
 "asi_curated": [
  "ASI01"
 ],
 "asi_scope": "in_scope",
 "asi_provenance": "curated_plus_rule",
 "asi_reason": "curated: ASI01 | added ASI02 (impact=tool_misuse)",
 "submitted_by": "EAI Internal"
}