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Microsoft Copilot Reprompt prompt-injection security flaw

Vulnerability
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Last updated
Happening score
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2 unique sources, 2 articles

Summary

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Reprompt is a Microsoft Copilot prompt-injection flaw that can let a crafted URL trigger invisible data exfiltration from an authenticated session. The abuse path uses the 'q' parameter and can be reached with a single click on a legitimate Microsoft link, without plugins or direct user interaction with Copilot. Microsoft addressed the issue after disclosure, and the flaw does not affect Microsoft 365 Copilot.

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Latest development: 20.05.2026 10:31

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Security Tool/Service
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Timeline

  1. 14.01.2026 16:00 1 articles · 5mo ago

    Varonis discloses Reprompt to Microsoft

    Initial Disclosure

    Varonis responsibly disclosed Reprompt to Microsoft after finding that Microsoft Copilot can execute prompts carried in a URL's 'q' parameter, letting a single click trigger injected instructions against an authenticated session.

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  2. 14.01.2026 16:00 1 articles · 5mo ago

    Microsoft fixes Reprompt in January 2026 Patch Tuesday

    Mitigation Patch Update

    Microsoft addressed the Reprompt flaw in January 2026 Patch Tuesday, and the remediation guidance is to apply the latest Windows security update to reduce risk from malicious Copilot links.

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  3. 14.01.2026 16:00 3 articles · 5mo ago

    Varonis details the Reprompt attack chain

    Technical Analysis Update

    Varonis described Reprompt as a Microsoft Copilot prompt-injection method that hides malicious instructions in a legitimate URL, uses the 'q' parameter to trigger actions, and can sustain invisible data exfiltration through P2P injection, a double-request technique, and a chain-request technique. The researchers said the attack can continue after the Copilot tab is closed, depends on the victim's authenticated session, and had not been detected in the wild.

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