Growing fatigue around Microsoft’s Copilot has coincided with a fresh reminder of the security challenges that come with deeply integrated AI assistants. While Microsoft continues to expand Copilot across its products—and faces mounting competition after Google secured a major AI partnership with Apple—researchers have revealed a now-patched vulnerability that could have exposed user data with minimal interaction.
Security firm Varonis disclosed details of an exploit dubbed “Reprompt,” which allowed attackers to exfiltrate information from Microsoft Copilot by convincing a user to click a specially crafted link. Microsoft confirmed the issue has been fixed as of January 13, 2026, aligning with its January Patch Tuesday updates.
How the Reprompt exploit worked
Unlike many phishing or malware attacks that rely on repeated user approvals, Reprompt required only a single click. The vulnerability abused the way Copilot handled prompts embedded in URLs, specifically through a common query parameter known as q, which is often used to prefill search boxes or text fields.
According to Varonis Threat Labs, attackers could hide malicious instructions inside this parameter. When a user opens the link, Copilot automatically interprets the embedded prompt and begins executing actions without further confirmation.
Researchers outlined several techniques that made the exploit particularly effective:
- Parameter-to-Prompt (P2P): Injecting instructions directly through the
qparameter. - Double-request technique: Triggering follow-up requests to bypass safeguards that only applied to an initial query.
- Chain-request method: Maintaining a silent, ongoing exchange with an attacker-controlled server to continue extracting data.
In practice, this could allow an attacker to query contextual information accessible to Copilot—such as recent activity, content viewed, or location data—depending on the permissions associated with the user’s account.
Scope and response
Microsoft stated that the flaw affected Copilot Personal, not Microsoft 365 Copilot, which operates under stricter enterprise controls, including auditing, data loss prevention, and administrative policies.
Varonis reported the vulnerability to Microsoft in late August 2025. After several months of investigation and remediation, Microsoft deployed a fix on January 13, 2026. The company has not indicated that the exploit was used on a large scale, but the disclosure highlights the risks associated with AI systems that can act autonomously based on user context.
A broader challenge for AI assistants
The Reprompt incident highlights a structural issue facing AI tools like Copilot: their usefulness depends on being able to “touch” files, history, and services. That same capability inevitably expands the attack surface. Closing one vulnerability does not eliminate the broader risk—it merely seals a single entry point.
As Microsoft, OpenAI, and their competitors race to make AI assistants more proactive and integrated, security researchers warn that prompt handling, context access, and automation will remain prime targets for exploitation. For users, the episode serves as a reminder that convenience and capability in AI often come with trade-offs that vendors are still learning to manage.
