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Microsoft warns OAuth error-flow abuse is driving phishing and malware

· 0 min read · Digital scams
Microsoft warns OAuth error-flow abuse is driving phishing and malware

Photo by BleepingComputer on BleepingComputer

What happened

Microsoft reports that attackers are weaponizing legitimate OAuth redirect/error handling to push victims from trusted-looking identity URLs to attacker-controlled pages.

Observed campaigns target government and public-sector organizations and use believable lures (e-signature requests, password reset notices, meeting invites, and financial/government-themed messages).

How the attack works

  1. Adversaries register a malicious OAuth app and set a hostile redirect URI.
  2. They trigger authorization requests with invalid parameters (such as bad scopes or prompt=none).
  3. The identity provider returns an error and redirects to the attacker URI as designed.
  4. Victims land on phishing pages or malware download paths.

Why this matters

  • This abuse leverages expected OAuth behavior, which can make detections harder.
  • Redirect chains can bypass user trust cues and some anti-phishing controls.
  • In some cases, attacker-in-the-middle tooling can steal session tokens and weaken MFA protections.

Defensive actions

  • Tighten OAuth app consent and app-registration controls.
  • Enforce Conditional Access and stronger identity protections.
  • Correlate detections across email, identity provider logs, and endpoint telemetry.
  • Block suspicious redirect patterns and inspect OAuth error-driven redirect traffic.

Bottom line

This is an identity-layer attack pattern, not just an email problem. Defenders should treat OAuth redirect abuse as part of core phishing and malware defense strategy.

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