One-Click Microsoft 365 Copilot Flaw Could Have Let Attackers Steal Emails, Files, and MFA Codes

A critical vulnerability in Microsoft 365 Copilot Enterprise Search, dubbed SearchLeak, could have allowed attackers to exfiltrate emails, files, and MFA codes with a single click. Discovered by Varonis Threat Labs, the flaw chains three bugs—Parameter-to-Prompt injection, a race condition in response rendering, and a Content Security Policy (CSP) bypass via Bing’s image endpoint—into a one-click attack path. The entry point is the ‘q’ parameter in the Copilot Enterprise Search URL, which interprets user input as instructions rather than a search string. An attacker crafts a URL that instructs Copilot to search the victim’s mailbox and embed an email title into an image URL. When the victim clicks, Copilot executes the search, and due to a race condition, the injected tag fires before sanitization. The CSP bypass uses Bing’s ‘Search by Image’ endpoint, which is allowlisted, to fetch the stolen data to an attacker-controlled server. Microsoft assigned CVE-2026-42824 with a CVSS score of 6.5 (Microsoft) or 7.5 (NVD) and mitigated the flaw on its backend. No exploitation has been observed in the wild. The attack can access emails, calendar details, MFA codes, password-reset links, and indexed files from SharePoint and OneDrive. Varonis previously demonstrated similar techniques in Reprompt and EchoLeak (CVE-2025-32711).

To mitigate risks, organizations should monitor for Copilot Search URLs with encoded payloads in the ‘q’ parameter and unusual outbound requests to Bing’s image endpoints. Tightening data-access governance to limit what Copilot indexes can reduce the potential impact of future leaks.