By: Lucas Ashbaugh, Nick Guarino, Max Gannon
Out of nowhere, someone responds to an email conversation that wrapped up months ago. It’s a real conversation that actually happened. Maybe it’s about a meeting, a job opportunity, or a reply to that problem you had over a year ago; this email is highly relevant to you. But something is off, the topic of the email is months out of date and now there is a weird error message.
This is a devious tactic, reviving an email conversation long dead – it’s the Zombie Phish.
Not Your Average Phish
The Cofense™ Phishing Defense Center (PDC) has recently been defending against an extensive Zombie Phishing campaign against multiple clients. Fraudsters hijack a compromised email account, and using that account’s inbox, reply to long dead conversations with a phishing link or malicious attachment. Due to the subject of the email being directly relevant to the victim, a curious click is highly likely to occur.
These Zombie Phish appear to use automatically generated infection URLs to evade detection. No two links are the same. These links are hidden behind unassuming “error” messages in the body of the email, providing an appealing scheme for users to fall victim to. Thus far, the PDC has observed two common Zombie Phishing templates that lead to malicious links. These email campaigns can be seen in Figures 1 and 2.
Another common hallmark of this campaign is the use of the .icu top-level domain (TLD), however this could change in the future. Example domains identified during this campaign, which abuse the .icu TLD, can be seen in Figure 3.
Figure 3 shows .icu domains associated with these campaigns.
Already, many of these domains have been shut down by their domain registrar after receiving reports of domain abuse. Figure 4 shows a domain associated with this campaign and the data that is collected and displayed by the registrar.
Figure 4, Courtesy of http://whois.domaintools.com
Additionally, the PDC has observed these phish using official organizational logos to add legitimacy to fake login pages – an example of such can be seen in figure 5. The pages are designed to impersonate an online portal of the target, including the company’s logo, and even its favicon. The end goal is credential theft of the victim.
Finally, any victim that visits the malicious website is “fingerprinted” using the host’s IP address as an identifier and upon entering credentials is immediately redirected to the same spam website seen by other victims. This is often via links obfuscated using URL shorteners (such as hxxps://href[.]li/). If the same host attempts to visit the phishing link again the spoofed login page is skipped and instead you are forwarded directly to the spam page. This finger-printing and the URL shortener obfuscation helps the attackers keep a low profile and continue their campaign unabated.
The tactic of “conversation hijacking” itself is by no means new, fraudsters have been hijacking compromised email accounts to dish out malware and phish as replies to prior conversations for years now. This technique is still popular because it makes victims much more likely to click on links and download or open files because their guard is down when these are within conversations already in their inbox. An ongoing and currently in the wild example of this is the Geodo botnet which has a history of inserting itself into existing email threads to deliver malicious documents that in turn download a sample of Geodo or other malware like Ursnif. However, the effectiveness of this tactic can depend greatly on the content of the conversations, a response to an automated advertising email is less likely to result in an infection than a response to a help desk support thread such as the one seen in Figure 6. Cofense IntelligenceTM has seen several Geodo campaigns consisting of responses to automated advertising emails indicating that, in some cases, the campaigns consist of indiscriminate responses to all emails in an inbox. Given that the volume of these “conversation hijacking” campaigns is still comparatively low, the smaller scope of these emails is likely limited by the number of ongoing conversations. Certain types of accounts therefore are more likely to draw threat actors direct attention and to induce them to invest additional effort and time into developing unique phishing campaigns for those accounts.
Preventing Your Personal Zombie Apocalypse
The PDC has compiled these quick tips to avoid losing your credentials (or your brains) to a Zombie Phish:
- Be alert for email subjects that may appear relevant but are from old conversations.
- Watch out for the hallmark green “error” button (pictured above in figure 1).
- Don’t trust attached documents simply because they are replying to a conversation.
- Mouse over buttons or links in suspicious messages to check them for the “.icu” top-level domain.
Cofense’s Phishing Defense CenterTM has observed that these campaigns have become increasingly clever, to combat this, training employees to be able to spot these types of emails is key. You can put down your nail-bats and pitchforks – a properly trained workforce is what is needed to defend your organization against the Zombie Phish hordes.
Cofense offers comprehensive phishing training to arm your employees with the weapons they need to protect your organization. And if you need reinforcements to help against the hordes, the Cofense Phishing Defense Center is happy to do battle with you.
All third-party trademarks referenced by Cofense™ whether in logo form, name form or product form, or otherwise, remain the property of their respective holders, and use of these trademarks in no way indicates any relationship between Cofense and the holders of the trademarks.
Indicators of Compromise: