Sophisticated Replay Attack Targets Gmail Users via Google Infrastructure.

In a new wave of sophisticated phishing attacks, cybercriminals are exploiting Google’s own infrastructure to target Gmail users with emails that appear legitimate—even passing standard security checks. This tactic, known as a replay attack, uses a method that manipulates Google’s email authentication system to bypass detection and steal user credentials.

Security researchers recently discovered that attackers have been leveraging DomainKeys Identified Mail (DKIM), an email authentication method used by Google, to replay genuine messages originally sent by Google itself. By resending these emails without altering their signed content, the attackers maintain the original DKIM signature, making the emails seem authentic and trustworthy to both users and email filters.

The phishing campaign typically begins when attackers acquire a legitimate Google email—such as a two-factor authentication or OAuth security alert. Without modifying the content, they then resend the message to a wide range of targets. The unchanged content ensures the DKIM signature remains valid, tricking email clients into treating the message as genuine.

Victims who open these messages are directed to phishing websites hosted on Google Sites. These fake pages convincingly imitate official Google login interfaces and prompt users to enter their account credentials. Once entered, this sensitive data is immediately captured by the attackers.

This tactic poses a significant threat because it effectively bypasses common defenses, including SPF, DKIM, and DMARC, that most email systems rely on to identify and block phishing attempts. The use of Google’s own tools and infrastructure further adds to the deception, making detection far more difficult.

Google has acknowledged the threat and stated that it is taking steps to mitigate this specific type of abuse. The company is updating its backend protections and urging users to remain vigilant.

To protect themselves, users are encouraged to:

  • Enable Multi-Factor Authentication (MFA) to provide an additional layer of security.
  • Be skeptical of unsolicited emails that create urgency or demand immediate action.
  • Carefully verify URLs before clicking any links, especially those requesting login credentials.
  • Report any suspicious emails directly to Google.

This incident highlights the evolving sophistication of phishing tactics and underscores the importance of continued user education and technical defense upgrades in today’s cybersecurity landscape.


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