SearchLeak let a single click on a malicious link pull emails, files and MFA codes out of Microsoft 365 Copilot
At a Glance
- Serious damage. Customer data affected, security incident, or financial losses $10k–$100k.
Independent project · aggregated from public reports and may be unverified — see the primary source below · not affiliated with or endorsed by any company or product named.
What Happened
Varonis Threat Labs disclosed CVE-2026-42824, a critical flaw in Microsoft 365 Copilot Enterprise Search. Clicking a single crafted link chained three bugs: injection of the URL parameter into the prompt, a rendering race condition, and abuse of Content Security Policy allowlisting to exfiltrate data through Bing's infrastructure. The attack could reach emails and calendar details, indexed SharePoint and OneDrive files, one-time and MFA codes, password-reset links, meeting notes and salary data. Because Copilot Enterprise is a managed service, tenant admins could not patch it themselves; Microsoft mitigated the flaw on its backend.
Case Analysis
Verified Facts
- CVE-2026-42824 was rated critical by Microsoft and found by Varonis Threat Labs
- The attack chained parameter-to-prompt injection, a rendering race condition and CSP allowlist abuse via Bing
- Microsoft mitigated the flaw on its backend because tenant admins cannot patch a managed service
Not Publicly Confirmed
- Whether the flaw was exploited in the wild before mitigation
- How many tenants were exposed
Operational Lessons
- URL parameters that flow into an assistant's prompt are untrusted input and must be isolated from tool-calling context
- A CSP allowlist that includes the vendor's own domains is an exfiltration channel, not a control
Primary Source
One-Click Microsoft 365 Copilot Flaw Let Attackers Steal Emails, Files and MFA Codes (The Hacker News)thehackernews.com ↗Case Record
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