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In a groundbreaking development in cybersecurity, researchers from Aim Labs have identified a critical vulnerability in Microsoft 365 Copilot, termed 'EchoLeak' (CVE-2025-32711). This flaw represents the first documented zero-click attack targeting an AI agent, enabling unauthorized access to sensitive user data without any user interaction.
Discovery and Disclosure
The vulnerability was discovered by Aim Labs in January 2025 and promptly reported to Microsoft. Recognizing the severity, Microsoft assigned it a critical rating and addressed the issue with a server-side patch in May 2025. Notably, Microsoft confirmed that no user action was required to implement the fix and found no evidence of real-world exploitation.
Technical Details of EchoLeak
EchoLeak exploits a Large Language Model (LLM) scope violation within Microsoft 365 Copilot. This flaw allows attackers to access a wide array of sensitive data, including:
  • Chat histories
  • OneDrive documents
  • SharePoint content
  • Teams conversations
The attack chain involves several sophisticated techniques:
  • Prompt Injection: Embedding malicious prompts within shared documents or emails to manipulate Copilot's behavior.
  • Automatic Tool Invocation: Triggering Copilot to perform unauthorized searches for additional sensitive information.
  • ASCII Smuggling: Utilizing invisible Unicode characters to embed sensitive data within hyperlinks, facilitating data exfiltration when users interact with these links.
This combination allows attackers to exfiltrate sensitive information seamlessly, posing significant risks to data security.
Industry Response and Mitigation
Microsoft's swift response included updating its products to mitigate the issue and integrating enhanced defense mechanisms to bolster Copilot's security. The company expressed gratitude to Aim Labs for their responsible disclosure, emphasizing the importance of collaboration in cybersecurity.
Security experts have highlighted the evolving sophistication of AI-enabled attacks. Stephen Kowski, Field CTO at SlashNext Email Security+, noted that the ASCII smuggling technique underscores the need for advanced threat detection systems capable of analyzing content across multiple communication channels. He emphasized the importance of leveraging AI and machine learning to identify subtle anomalies that traditional security measures might miss.
Implications for AI Security
The EchoLeak incident serves as a stark reminder of the potential vulnerabilities inherent in AI-driven tools. As AI becomes increasingly integrated into enterprise environments, the attack surface expands, necessitating robust security measures. Organizations are urged to:
  • Implement Advanced Threat Detection: Deploy systems that can detect and respond to AI-specific attack vectors, such as prompt injections and data exfiltration techniques.
  • Enhance Data Loss Prevention (DLP) Measures: Utilize DLP solutions to monitor and prevent unauthorized data transfers, especially through AI-generated content.
  • Conduct Regular Security Audits: Perform frequent assessments of AI tools to identify and mitigate potential vulnerabilities.
  • Educate Employees: Provide ongoing training on emerging threats associated with AI tools to foster a culture of security awareness.
Conclusion
The discovery of EchoLeak underscores the critical need for continuous vigilance and proactive security measures in the era of AI integration. While Microsoft's prompt response has mitigated this specific threat, the incident highlights the broader challenges in securing AI systems against sophisticated, zero-click attacks. As AI technologies evolve, so too must the strategies to protect them, ensuring that innovation does not come at the expense of security.

Source: Windows Central Researchers uncover first "zero-click" attack on Microsoft 365 Copilot, enabling data access without user interaction
 

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