Microsoft 365 EOP
By Kaleb Kirk, Cofense Phishing Defense Center
Last month, the Cofense Phishing Defense Center (PDC) observed a new phishing trend wherein threat actors spoofed WebEx pages to harvest Office365 (O365) credentials. Since the posting of the original blog, the PDC has seen an increase in the number of similarly themed WebEx phishing attacks, yet another example of attackers leveraging the rapid shift to remote work in light of COVID-19 concerns. As many organizations and their workforce are increasingly dependent on remote working tools and solutions, reducing the attack surface (the number of different approaches a threat actor can use to enter or extract data) of such online platforms and services is becoming even more critical.
Attackers know this and are constantly looking at ways to circumvent detection by secure email gateways and position themselves between users and legitimate services. The WebEx phishing campaign is a prime example, slipping past email protection to dupe users into providing their credentials out of fear they will be unable to use the service and perform their job otherwise. It’s therefore not a surprise the PDC has seen an increase in phishing attacks that spoof legitimate, business critical services.
While this blog focuses on a new phishing campaign imitating WebEx, this style of attack can and has taken multiple forms, mimicking many different legitimate web services. Luckily however, once an end user knows some of the telltale signs, it’s often easy to identify what is truly legitimate and what is fake.
Figures 1-2: Email Body
Upon an initial glance, this email may appear innocuous enough. It has the look and format one would likely expect when receiving an email from Cisco. The style is professional, the layout of the email isn’t mangled or chaotic, and it appears legitimate – an intentional and easy tactic to pull off. All the threat actor required was a real WebEx email to copy from in order to duplicate the style and alter select elements for nefarious purposes. The sender address appears to come from WebEx. However, this is what is known as the “friendly” from address – while the recipient sees the displaying address, which appears to be authentic, the email headers reveal a very different story. The problem with a “friendly” sender address is that it is easily spoofed by attackers; it’s a well-known, simple trick designed to convince the recipient that an email is legitimate.
Looking beyond simple aesthetics, however, other indicators of phishing are evident. The subject line indicates there is an issue with SSL certificates that requires the user to sign in and resolve. This is referenced further in the body of the email, providing a sense of legitimacy and enticing them to open the email and read it.
The wording of the email also employs scare tactics that are prevalent in phishing attacks. The recipient is informed there is a problem that has caused their service to become deactivated and the user must log-in and authenticate by clicking the link. Verbiage like this is often used to coerce the end user into clicking on a link or attachment in haste before they have time to fully think it through – a key tactic used by threat actors in phishing campaigns.
Finally, the link itself reveals something else is fishy about this alert. Hovering over the button shows the embedded link is not, in fact, a WebEx page, but a SendGrid link, a legitimate customer communication service used by marketing professionals. SendGrid links are commonly used in phishing attacks, as they require minimal effort.
Figure 3: Phishing Page, Step 1
Upon clicking the SendGrid link, the user is redirected to a phishing page, as seen in Figure 3. The only difference between a legitimate WebEx login page and this phishing page is the URL itself, suggesting the attacker conducted some form of web scraping to create an intentionally benign looking and familiar login page for the end user. Web scraping, essentially, is the practice of using a tool to automatically copy data from a website and create a convincing copy.
Figure 4: Phishing Page, Step 2
Deception quickly falls apart when reviewing the URL, however; while designed to look like the actual URL, there actually isn’t a portion that includes ‘webex.com’. The numerous dashes, coupled with one very long word followed by ‘index.php’ is not reflective of a professional link, suggesting the phishing URL was registered to appear legitimate at first glance. While phishers commonly make a valiant effort for their pages to look legitimate, looking at the address bar generally reveals if it’s legitimate. Misspelling, similar looking words and strange top-level domains are common tricks used by attackers to guile end users for just long enough to not question it.
While the initial phishing page only requests the user’s email address, the following page then changes URLs from “index.php” to “step2.php” and asks for the user’s password- this is another indicator the site is not legitimate, as the specific internals of which php file is being invoked for this webpage would be usually be hidden to the user.
Figure 5: Final redirect to official WebEx login page
As the final stage of attack, when the user enters their credentials on the page shown in Figure 5 above, the user is then redirected to WebEx’s real sign-in page. At this point, the malicious actor now has the user’s credentials, but it is in their best interest to ensure the user is unaware that a successful credential phishing attack occurred, giving the threat actors time to make use of newly stolen log-in details. The final redirect to WebEx’s legitimate log-in page may make the end user believe there was a log-in error and they need to log-in again. A common theme in a many phishing attacks is appealing to and preying on the feeling that nothing is amiss and there is nothing to question about the experience. In the meantime, threat actors gain precious time to do damage while the end user moves on with his or her workday.
Figure 6: Open Directory
A final interesting finding about this phishing campaign is the main domain itself, which reveals an open directory. This open directory shows the files included in the phishing page: images, fonts, .css files, and more. Although finding this directory was easy, it isn’t necessary to hide it, as most end users will only go through to login rather investigating into the internals of the site. However, it must be noted no professional website allows access to its file directories in this way. If reached, it is an almost sure-fire way of immediately identifying a phish.
How Cofense Can Help
Visit Cofense’s Remote Work Phishing Infocenter to stay up to date as threats evolve. Our site is updated with screenshots and YARA rules as we continue to track campaigns.