Phishing Campaign Uses Internal Email to Trick Employees into Sharing Office 365 Credentials

A campaign targeting Office 365 customers used a compromised internal email for phishing messages, giving much more credence to an email that people would otherwise dismiss immediately.

Phishing emails are a fact of life. Most are caught by corporate security nets and even by commonly used email services. They are also easier to spot, especially if the recipient pays attention to the sender’s real address.

Unfortunately, spotting a phishing email becomes much more difficult when it originates from an internal email address. It looks credible and bypasses security measures. Even trained employees could mistake the email for a legitimate one, although there are other markers to look out for.

“The attacker launched an attack from an IP located in the United Kingdom, which is suspicious because this sender never sends from the UK, and the recipient rarely receives emails from there either,” say the researchers from Abnormal Security. “The attacker leverages a compromised account to send internal phishing attacks. The email itself is simple and masquerades as an encrypted message notification related to a OneDrive for Business file.”

If the employee clicks on the link, it redirects to a phishing site, where attackers ask for his Office 365 credentials. Furthermore, the email doesn’t show the URL, so as to avoid suspicion.

“The link in the email is hidden in text of the company’s name, and the link hosted on the Russian domain is concealed in the text “VIEW ONLINE / DOWNLOAD.” After clicking the links, victims are taken to a phishing page tailored specifically to their company,” the researchers say.

Mitigation for phishing usually starts with employee training. It pays to be extra careful of any message, especially from inside the company, and to be wary when asked for credentials. If there are ever any doubts, contacting the IT department is always an option.