SearchLeak vulnerability in Microsoft 365 Copilot exposes sensitive data
Researchers at Varonis Threat Labs discovered SearchLeak, a three-stage vulnerability chain in Microsoft 365 Copilot Enterprise that combines prompt injection with other web flaws to enable attackers to steal sensitive data including emails, files, and authentication codes. Microsoft issued a critical patch (CVE-2026-42824) in June 2026.
What happened
Varonis Threat Labs uncovered a three-stage vulnerability chain called SearchLeak that chains parameter-to-prompt injection with an HTML injection race condition and a Content Security Policy bypass via Bing server-side request forgery to enable one-click data theft from Microsoft 365 Copilot Enterprise Search.
The attack exploits Microsoft's safety guardrails by combining three separate attacks that individually would not work, but together circumvent protections that prevent the AI assistant from sending data to an attacker.
Reported impact
SearchLeak can be used to exfiltrate inbox emails, two-factor authentication codes, OneDrive files, SharePoint documents, meeting invites, notes, and other indexed business content that a user has access to within an organization.
The blast radius could extend further depending on how Microsoft 365 is connected to an organization's environment, potentially exposing additional sensitive data.
Index analysis
The vulnerability leverages parameter-to-prompt injection via a specially crafted URL query parameter to manipulate Copilot's search functionality.
Governance controls
Microsoft patched the vulnerability as CVE-2026-42824 earlier in June 2026, rating it 10/10 critical severity.
Classification
Sources and evidence
This record was researched and written by the Index, based on the following original reporting.