How a Single Click Can Compromise Your Copilot Data

A New Security Threat: Reprompt

Security experts have uncovered a novel vulnerability labeled 'Reprompt' which allows data theft from Microsoft's Copilot AI assistant with just a single click, circumventing existing security measures.

Unveiling the Reprompt Flaw

This flaw, detailed by Varonis Threat Labs, affects Microsoft Copilot Personal. The issue lies in its ability to let cybercriminals exploit the system through a seemingly innocuous URL, giving them access to sensitive information stealthily.

The attack can be initiated without user interaction with Copilot other than clicking a specific link. This click triggers exploitation of the 'q' URL parameter, allowing attackers to pass contaminated prompts to Copilot and request previously submitted data, including personal identifiers.

Despite closing the Copilot chat, the attacker's control persists, enabling them to quietly extract information without further user interference, as researchers point out.

The Mechanics of the Reprompt Exploit

The exploit works by chaining together three sophisticated techniques, making it highly elusive. Monitoring tools situated on either user or client sides typically fail to detect this attack, as it skillfully evades inbuilt security protocols.

Data leakage occurs slowly, allowing the perpetrator to utilize responses to formulate successive harmful instructions.

Microsoft Steps In

Microsoft was informed about the Reprompt flaw on August 31, 2025. Swift actions followed, resulting in a patch before the vulnerability became publicly known, ensuring Microsoft 365 Copilot's enterprise users remained unaffected.

Steps to Enhance Security

As AI technologies advance, they frequently encounter security challenges. Known vulnerabilities, design oversights, and security threats are not uncommon discoveries.

Phishing, as utilized in this scenario, relies heavily on recipients clicking deceitful links, thus vigilance in handling unknown links is crucial. Protect yourself by exercising caution with links from unfamiliar sources.

Be mindful about sharing sensitive data. Particularly with AI tools like Copilot, watch out for unusual prompts or data requests that could suggest unauthorized activity.

Varonis underscores the importance of approaching new technologies prudently, noting that external inputs can often betray users. They advise strict scrutiny of URLs and external inputs, urging for robust validation and overall process chain safety measures.

Implement measures to prevent repeated prompts and linked actions from progressing past the initial stage to bolster defenses against such vulnerabilities.