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Microsoft Warns Attackers Are Abusing OAuth Redirects to Deliver Malware to Government Targets

Microsoft says takedowns of malicious apps have not stopped related activity, prompting calls for tighter OAuth governance.

Overview

  • Researchers detail phishing campaigns that craft OAuth authorization requests with invalid scopes or silent prompts to trigger error-handling redirects to attacker domains.
  • Targets receive emails themed around e‑signatures, Teams recordings, password resets, or political and financial topics, with links in the message or embedded within PDFs.
  • Actors pass victim emails through the OAuth state parameter to auto-populate phishing pages, using mass-sending tools, custom Python and Node.js scripts, and cloud services.
  • Some operations route users to EvilProxy adversary‑in‑the‑middle kits to capture credentials and session cookies instead of delivering malware directly.
  • In malware-delivery cases, redirects auto-download ZIP files containing LNK and HTML smuggling loaders that execute PowerShell, side‑load a malicious DLL via steam_monitor.exe, decrypt a payload, and establish C2; Microsoft disabled observed OAuth apps and recommends limiting user consent, pruning overprivileged apps, and enforcing Conditional Access with cross-domain detection.