Summary:
In a complex threat landscape undergoing constant evolution, targeted phishing campaigns have become more sophisticated due to attackers leveraging new techniques and analyzing the platform-specific behaviors of organizations’ defenses they target. Spearphishing is the preferred initial access technique when targeting corporate executives and their high-value credentials. Over the past few months, enterprises have observed a pattern of sophisticated spear phishing attempts targeting their executives, with some specifically targeting their mobile devices. These attacks impersonate trusted business platforms and internal communications and leverage a mobile device's features to improve the attacks' effectiveness. zLabs researchers analyzed a targeted campaign that leveraged DocuSign to harvest credentials from their company executives. Their analysis revealed an interesting attack chain incorporating advanced evasion techniques, mobile-specific targeted phishing links inside PDF files, and sophisticated infrastructure designed to circumvent traditional security controls while maintaining a convincing corporate appearance. This attack was identified and blocked before any credentials were compromised.

The attack chain begins with a well-crafted email geared at executives that demonstrates the threat actor’s willingness to perform reconnaissance and research in advance of the attack. (in this case: intrusion attempt). The initial payload was masquerading as a DocuSign document to evoke a sense of urgency in the potential victim. The phishing link is distributed using a legitimate domain from a sales and marketing platform which obscures the attacker’s origin. The link redirects to a high-reputation domain to leverage its credibility for evading detection from systems that classify sites as risky using their reputation or domain creation date. The attackers also implement Captcha verification to help bypass automated detections. Attackers used device fingerprinting to ensure they delivered tailored attack paths only against mobile devices, abandoning the attack if it was attempted against a desktop. If the link was accessed via a mobile device, a cloned Google sign-in page designed to steal credentials was presented to the mobile user. The phishing attack was received on December 9th, 2024, and the domain hosting the final phishing site was created recently on December 5th, 2024.

Security Officer Comments:
The level of sophistication illustrated in this attack chain highlights the advanced nature of targeted corporate missing (mobile-specific phishing). As DocuSign is widely used in corporate environments, it acts as an effective delivery mechanism. The IP address hosting the final phishing site belongs to Cloudflare infrastructure, highlighting the increasing exploitation of these legitimate services for malicious purposes. zLabs was able to identify additional phishing activity that they traced back to mid-May 2024 originating from the same IP address used in this attack. Running parallel to the email-based campaign, the attacker incorporated PDF-based phishing attempts that also mimicked DocuSign workflows into the campaign. By incorporating rapid infrastructure rotation and PDF-based delivery, the adversary creates significant challenges for an organization’s traditional detection mechanisms. This multi-faceted initial access strategy underscores the importance of cybersecurity monitoring solutions that include mobile-aware phishing protection.

Suggested Corrections:
Users should always be cautious of individuals or organizations that ask for personal information. Most companies will not ask for sensitive data from their 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://hackread.com/mobile-phishing-executives-fake-docusign-links/

https://www.zimperium.com/blog/mobile-spear-phishing-targets-executive-teams/