Cyber Security Threat Summary:
A large-scale operation focused on harvesting credentials has emerged, utilizing a legitimate email newsletter program called SuperMailer to distribute a substantial volume of phishing emails. The intention behind this campaign is to bypass secure email gateway protections. Recent findings from Cofense, as of May 23, reveal that SuperMailer-generated emails account for a significant portion of all credential phishing attempts, constituting approximately 5% of the firm's telemetry for May. The campaign's magnitude is rapidly escalating, with the overall monthly volume witnessing more than a twofold increase in three out of the past four months. This growth is noteworthy, especially considering the general rise of credential phishing activities. Brad Haas, a cyber threat intelligence analyst at Cofense and the researcher behind the report, explained that the threat actors orchestrating the campaign leverage SuperMailer’s customization features and sending capabilities in combination with evasion tactics. This enables them to create tailored, authentic looking-emails that reach inboxes across various industries.

“What makes the numbers even more interesting is the fact that SuperMailer is a somewhat obscure German-based newsletter product that has nowhere near the scale of more well-known email generators such as ExpertSender or SendGrid, Hass tells Dark Reading — yet it's still behind wide swathes of malicious emails. "SuperMailer is desktop software that can be downloaded for free or for a nominal fee from a number of sites that may be completely unassociated with the developer," he says. "A free version of SuperMailer was released on CNET in 2019, and since that point has had approximately 1,700 downloads. This number is low in comparison to many popular software downloads, but we do not have any other information on the number of legitimate organizational users." SuperMailer did not immediately respond to Dark Reading's request for comment. But since the clients are propagated via third-party websites and have no server or cloud component, Haas notes that SuperMailer's metaphorical hands are tied when it comes to rooting out the activity. "In the past, we've seen large, cloud-based services abused to send phishing emails or create unique URL redirects pointing to phishing pages, but those services often catch and combat the activity after a period of time," he says. "We do not know the extent to which the SuperMailer developer is capable of fighting this abuse." That in of itself makes SuperMailer attractive to cybercriminals. But the other reason is that it offers an attractive disguise for getting past SEGs and ultimately end users, thanks to some unique features” (Dark Reading, 2023).

In the case of SuperMailer, its compatibility with various email systems provides an advantage to threat actors. By distributing their operations across multiple services, they decrease the chances of their emails being flagged as unwanted by secure email gateways or upstream email servers due to poor reputation. The threat actors like possess access to compromised accounts and utilize SuperMailer’s sending capabilities to rotate through them, as noted in Haas’s report.

Security Officer Comments:
These campaigns generated by SuperMailer also exploit template customization features, enabling automatic personalization with recipient details, organization names, email reply chains, and more. Such customization significantly enhances the authenticity and credibility of the phishing emails. Additionally, the software does not flag open redirects, which are legitimate web pages that automatically redirect to any URL specified as a parameter. This allows malicious actor to employ completely legitimate URL’s as initial phishing links. Haas highlights that secure email gateways may only check the content or reputation of the legitimate website if they do not follow the redirect.

Suggested Correction(s):
Users should always be cautious of individuals or organizations that ask for personal information. Most companies will not ask for sensitive data from its customers. If in doubt, users should verify with the company itself to avoid any potential issues.

Users should always take a close look at the sender’s display name when checking the legitimacy of an email. Most companies use a single domain for their URLs and emails, so a message that originates from a different domain is a red flag.

As a general rule, users should not click links or download files even if they come from seemingly “trustworthy” sources.

Check for mismatched URLs. While an embedded URL might seem perfectly valid, hovering above it might show a different web address. In fact, users should avoid clicking links in emails unless they are certain that it is a legitimate link.

Users should always be on the lookout for any grammatical errors and spelling mistakes. Legitimate companies will often employ proofreaders and editors who ensure that the materials they send out are error-free.

Users should not be frightened or intimidated by messages that have an alarmist tone. They should double check with the company if they are uncertain about the status of their accounts.

Phishing emails are designed to be sent to a large number of people, so they need to be as impersonal as possible. Users should check whether the message contains a generic subject and greeting, as this can be a sign of a phishing attempt.

Although not every end user has access to advanced anti-phishing software, they can still use the built-in protection of their email clients to filter messages. One example is setting the email client to block all images unless approved.

Legitimate companies will never send confirmation emails unless there are specific reasons for doing so. In fact, most companies will avoid sending unsolicited messages unless it’s for company updates, newsletters, or advertising purposes.

Users should always take the context of an email or message into account. For example, most online accounts do away with viewable member numbers, so users should be wary if they receive emails containing a “member number” for services that generally don’t use them.

It is important to take note of unusual information in the text of the message. Any mentions of operating systems and software that are not typically used by consumers can often be indicators of a phishing attempt.

If it seems suspicious, it probably is. Users should always err on the side of caution when it comes to sending out personally identifiable information through messages and emails.

Link(s):
https://www.darkreading.com/endpoint/supermailer-abuse-email-security-super-sized-credential-theft