Disclosed vulnerability
Microsoft Copilot Cowork: poisoned Skill makes the agent send itself a Teams message that leaks pre-authenticated SharePoint/OneDrive download links
AIR-2026-0120 AIR record · 2026-05-microsoft-copilot-cowork-exfiltrates-files
From the supporting source
unlike other sensitive actions, sending emails and Teams messages to the active user does not require human approvalpromptarmor.com
The record
Disclosed
2026-05-26
Vendor
Microsoft
Product
Microsoft Copilot Cowork (Microsoft 365)
Risk domain
Privacy › Data exfiltration channels
Also touches
Supply chain vulnerabilities
System type
Generative model
Who acted
Agent acted — the agent sent itself a Teams message leaking pre-authenticated links
Attack surface
Enterprise assistant
Autonomy level
Semi-autonomous
Initial vector
Malicious skill
Impact type
Data exfiltration
Confidence
High
Submitted by
EAI Internal
Crosswalk
- OWASP Agentic Top 10 (2026)
- ASI02 – Tool Misuse and Exploitation
- MITRE ATLAS
- AML.T0024 – Exfiltration via AI Inference API
- NIST AI RMF
- MAP 4.2
- EU AI Act
- Article 10
- ISO/IEC
- TR 24028; 23894
- AIUC-1
- A. Data & Privacy
- Scope
- tool misuse
- Mitigation
- Monitor network traffic for anomalous patterns; Restrict egress destinations.
- Taxonomy
- Enkrypt AI agent risk taxonomy · Black-Box Red Teaming of Agentic AI: A Taxonomy-Driven Framework for Automated Risk Discovery
Blast radius
M365 tenants where users can upload or share Copilot Cowork Skills
Capability abused
Defense & remediation
Recorded defense
human approval required for sensitive actions
Guardrail kinds
Human approval
Guardrail outcome
Silent
Fix shipped
unknown; mitigation is SharePoint download policy restriction
Taxonomy & references
Curator notes
PromptArmor. The approval carve-out for self-directed Teams/email messages is the pivot: the agent is steered into sending itself a message containing HTML image tags that fire network requests to the attacker when rendered, carrying Microsoft Graph pre-authenticated file download links for SharePoint/OneDrive documents. Linked from Simon Willison's prompt-injection and exfiltration-attacks tags. verified_quote is a verbatim clause from the page.
Cite as
Enkrypt AI. "Microsoft Copilot Cowork: poisoned Skill makes the agent send itself a Teams message that leaks pre-authenticated SharePoint/OneDrive download links". AIR, AIR-2026-0120. https://agentincident.vercel.app/i/AIR-2026-0120/ (accessed 2026-10-19).