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Summary
On July 12, 2022, Microsoft researchers disclosed a large-scale phishing campaign that has targeted more than 10,000 organizations since September 2021. The campaign used adversary-in-the-middle (AiTM) phishing sites to proxy the authentication process and hijack the victims’ Office 365 session cookies.
With these stolen session cookies, the attackers were able to authenticate to Office 365 as the victims and perform a whole slew of malicious activities from the user’s mailboxes, such as business email compromise (BEC).
Attackers have been using real-time active directory authentication since late 2020 and last year, researchers identified a new fingerprinting technique, called PHOCA, that makes it possible to identify AiTM phishing kits. There are also phishing attacks that make use of malicious OAuth apps. This particular attack is different and effective because it bypasses corporations’ MFA protections, since capturing a user’s session cookie enables an attacker to skip the authentication workflow (including MFA) altogether.
Threat
The attackers used the Evilginx2 phishing kit to carry out the AiTM attacks. The initial lures were emails that contained “important” voice messages, which in reality ended up downloading malicious html attachments. When a victim clicked on these attachments, they were redirected to the Office 365 credential-stealing landing pages.
Contrary to the traditional phishing setup, AiTM phishing does not require a custom built phishing site, but rather the requests are proxied to and from the actual website. The phishing site creates a proxy to the organization’s Azure Active Directory login portal (login.microsoftonline.com). Essentially, the attackers open up two lines of communication: one from the victim to the attacker-controlled phishing site and one from the attacker-controlled site to the real Office 365 login portal. Hence the URL used by the phishing campaign would be different from the original website, which is not the case in other phishing attacks like device code phishing attacks.