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.