Have you ever imagined that a simple click could compromise your most sensitive data? With the discovery of Reprompt, an attack technique targeting Microsoft Copilot, this concern becomes a reality. Dive into the details of this threat and find out how it was quickly neutralized.
The 3 key facts not to miss
- Reprompt is an attack technique exploiting a vulnerability in Microsoft Copilot, allowing hackers to control sessions and access sensitive data.
- The flaw was discovered by Varonis security researchers and was fixed by Microsoft in January 2026.
- This vulnerability only affected Copilot Personal, leaving Microsoft 365 Copilot for businesses untouched.
Discovery of Reprompt
The Reprompt attack technique was brought to light by Varonis security researchers. By analyzing the operation of Microsoft Copilot, they discovered that it could be manipulated through a simple URL. Using the “q” parameter in this URL, attackers could insert commands that executed automatically when the page was loaded. This method exploits a click on a phishing link, making the attack both discreet and potentially devastating.
Operation and impact of the attack
Once the victim clicks on the trapped link, the active Copilot session remains connected, even if the user closes the tab. This allows hackers to send additional commands in the background to extract data, such as conversation history. The Reprompt method uses repetition and chaining of requests, making it difficult for security tools to detect data exfiltration.
Microsoft’s response and resolution
Varonis alerted Microsoft to this vulnerability in August 2025. In response, Microsoft promptly reacted by integrating a fix in its January 2026 Patch Tuesday security update. Thanks to this quick intervention, no abusive exploitation of this flaw was reported. Copilot Personal users were advised to update their systems to protect themselves from any potential attacks.
Differences between Copilot Personal and Microsoft 365 Copilot
It is important to note that the Reprompt vulnerability only affected Copilot Personal. Microsoft 365 Copilot, primarily used by businesses, was not affected. This distinction is crucial for companies that rely on Microsoft 365 for their daily operations, ensuring them enhanced security.
Microsoft Copilot: evolution and security
Microsoft Copilot, launched as an AI-based assistance tool, quickly gained popularity. Designed to integrate various Microsoft applications, it offers users an interactive and personalized experience. However, like any technological tool, it is not immune to vulnerabilities. The discovery of Reprompt highlighted the need to maintain constant vigilance and strengthen security measures. Microsoft, in response to this threat, demonstrated its commitment to user security by quickly fixing the flaw and continuing to monitor potential threats. This proactive approach is essential to ensure the secure and reliable use of their products.