Hackers using Captcha to hide the presence of malware and to evade email security gateways. By using this technique attackers show that email is sent human and evades detection.
Attackers use various social engineering methods to trick the users to believe the emails is from a legitimate source, here the email’s are from a compromised account at @avis.ne.jp.
Hidden Malicious Page Behind Captcha
Cofense identified a new email campaign that alerts recipients that they received a new voicemail message. The voice was with a preview that tempts users to listen to the full message.
The email contains a play button which has an embedded hyperlink pointing to the page that contains captcha, this step is to bypass the automated analysis tools and to bypass secure email gateways.
Once the user click’s on the link they get directed to the captcha page, once the captcha check completed users taken to the main phishing page that hosted on MSFT infrastructure.
The phishing page asks the user to select a Microsoft account to log in when the victim login all their credentials are captured.
“Both pages are legitimate Microsoft top-level domains, so when checking these against domain reputation databases we receive a false negative and the pages come back as safe,” reads Cofense report.
The attack method is nothing new, the important part is the Captcha page which makes the attack more successful by evading the security controls placed.
Email Header Analysis always helps you in preventing such malicious threat, emails are the critical business asset and they need to be secured.