Disclosed vulnerability
Microsoft Copilot Cowork sandbox bypass: malicious Skills reach attacker servers through the out-of-sandbox file sync service for C2 and exfiltration
AIR-2026-0201 AIR record · 2026-08-microsoft-copilot-cowork-sandbox-bypass
From the supporting source
A sandbox bypass in Microsoft Copilot Cowork allowed malicious Skills to communicate with attacker servers to retrieve commands and exfiltrate any data the agent could access.promptarmor.com
The record
Disclosed
2026-08-19
Vendor
Microsoft
Product
Microsoft Copilot Cowork
Risk domain
Tool misuse › Supply chain vulnerabilities
Also touches
Privilege escalation, Data exfiltration channels
System type
Generative model
Who acted
Agent acted — the Skill reached attacker servers through the file sync service
Attack surface
Enterprise assistant
Autonomy level
Semi-autonomous
Initial vector
Malicious skill
Impact type
Data exfiltration, Remote control
Confidence
High
Submitted by
EAI Internal
Crosswalk
- OWASP Agentic Top 10 (2026)
- ASI04 – Agentic Supply Chain Vulnerabilities
- MITRE ATLAS
- AML.T0040 – AI Supply Chain Compromise
- NIST AI RMF
- MAP 4.1
- EU AI Act
- Annex III §2
- ISO/IEC
- TR 24028; 42001; 23894
- AIUC-1
- B. Security
- Scope
- tool failure
- Mitigation
- Scan dependencies and container images for vulnerabilities; Use trusted sources.
- 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 using Copilot Cowork with user- or org-shared Skills
Capability abused
Defense & remediation
Recorded defense
Copilot Cowork code sandbox with network restrictions
Guardrail kinds
Sandbox isolation, Permission scope
Guardrail outcome
Silent
Fix shipped
mitigated 2026-08-19
Taxonomy & references
Curator notes
PromptArmor. Reported 2026-06-24, mitigated 2026-08-19. The file sync service sits outside the sandbox and accepts arbitrary URLs, giving a two-way channel. Notable secondary finding: 'Processes running in the background in the sandbox continue to execute even when an agent's turn ends' - clicking stop does not halt the attack. Data reachable included Outlook, SharePoint, Teams, plugins and chat history.
Cite as
Enkrypt AI. "Microsoft Copilot Cowork sandbox bypass: malicious Skills reach attacker servers through the out-of-sandbox file sync service for C2 and exfiltration". AIR, AIR-2026-0201. https://agentincident.vercel.app/i/AIR-2026-0201/ (accessed 2026-10-19).