Security News > 2022 > September > Microsoft Exchange servers hacked via OAuth apps for phishing
Microsoft says a threat actor gained access to cloud tenants hosting Microsoft Exchange servers in credential stuffing attacks, with the end goal of deploying malicious OAuth applications and sending phishing emails.
"The unauthorized access to the cloud tenant enabled the actor to create a malicious OAuth application that added a malicious inbound connector in the email server."
The attacker then used this inbound connector and transport rules designed to help evade detection to deliver phishing emails through the compromised Exchange servers.
In contrast, the OAuth application remained dormant for months between attacks until it was used again to add new connectors and rules before the next wave of attacks.
Microsoft says this threat actor was linked to campaigns pushing phishing emails for many years.
"The actor's motive was to propagate deceptive sweepstakes spam emails designed to trick recipients into providing credit card details and signing up for recurring subscriptions under the guise of winning a valuable prize," Microsoft further revealed.
- Microsoft SQL servers hacked in TargetCompany ransomware attacks (source)
- Phishers use custom phishing kit to hijack MFA-protected enterprise Microsoft accounts (source)
- Microsoft accounts targeted with new MFA-bypassing phishing kit (source)
- Snapchat, Amex sites abused in Microsoft 365 phishing attacks (source)
- Microsoft: Exchange ‘Extended Protection’ needed to fully patch new bugs (source)
- Phishing attack abuses Microsoft Azure, Google Sites to steal crypto (source)
- SquarePhish: Advanced phishing tool combines QR codes and OAuth 2.0 device code flow (source)
- Microsoft Warns About Phishing Attacks by Russia-linked Hackers (source)
- Microsoft will disable Exchange Online basic auth next month (source)
- Microsoft 365 phishing attacks impersonate U.S. govt agencies (source)