A novel single-click assault focusing on Microsoft Copilot Private that allows attackers to silently exfiltrate delicate consumer information. The vulnerability, now patched, allowed menace actors to hijack classes by way of a phishing hyperlink with out additional interplay.
Attackers provoke Reprompt by sending a phishing electronic mail with a reputable Copilot URL containing a malicious ‘q’ parameter, which auto-executes a immediate upon web page load.
This Parameter-to-Immediate (P2P) injection leverages the sufferer’s authenticated session, persisting even after closing the tab, to question private particulars like usernames, areas, file entry historical past, and trip plans.
The assault chain then employs server-driven follow-ups, evading client-side detection as instructions unfold dynamically.
Assault Chain (Supply: Varonis)
Varonis detailed three core methods enabling stealthy information theft, bypassing Copilot’s safeguards designed to dam URL fetches and leaks.
TechniqueDescriptionBypass MethodParameter-to-Immediate (P2P)Injects directions by way of ‘q’ parameter to auto-populate and execute prompts stealing dialog reminiscence or information.Injects directions by way of ‘q’ parameter to auto-populate and execute prompts, stealing dialog reminiscence or information.Double-RequestCopilot’s leak protections apply solely to preliminary requests; repeats actions twice to succeed on the second strive.Instructs “double test… make each operate name twice,” exposing secrets and techniques like “HELLOWORLD1234!” on retry.Chain-RequestServer generates sequential prompts based mostly on responses, chaining exfiltration phases indefinitely.Progresses from username fetch to time, location, consumer information abstract, and dialog matters by way of staged URLs.
These methods make information exfiltration undetectable, as prompts look innocent whereas data is progressively leaked to attacker servers.
Delicate Information Exfiltrated (Supply: Varonis)
Reprompt focused Copilot Private, built-in into Home windows and Edge for shopper use, accessing prompts, historical past, and Microsoft information like current recordsdata or geolocation.
Enterprises utilizing Microsoft 365 Copilot have been unaffected by Purview auditing, tenant DLP, and admin controls. No in-the-wild exploitation occurred, however the low barrier to a single-click electronic mail or chat assault posed dangers to information reminiscent of monetary plans or medical notes, as proven within the assault diagrams.
Varonis responsibly disclosed the difficulty to Microsoft on August 31, 2025, with a repair deployed by way of the January 13, 2026, Patch Tuesday. Customers ought to apply the most recent Home windows updates instantly to dam remnants.
In contrast to prior flaws like EchoLeak (CVE-2025-32711), Reprompt required no paperwork or plugins, highlighting URL parameter dangers in AI platforms.
Organizations should deal with AI URL inputs as untrusted and implement persistent safeguards throughout chained prompts. Copilot Private customers ought to scrutinize pre-filled prompts, keep away from untrusted hyperlinks, and monitor for anomalies like unsolicited information requests.
Distributors like Microsoft are urged to audit exterior inputs deeply, assuming insider-level entry in AI contexts to preempt related chains.
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