The ZBOT (aka Zeus) trojan has been one of the most prolific and enduring malware families of the past 20 years. After its first appearance in 2006, its source code was leaked in 2011, leading to a plethora of new variants that plagued organizations over the succeeding years.
One of the most notable recent ZBOT variants is Zloader. First compiled under the name Silent Night in late 2019, it has evolved from being an information stealer to a multipurpose dropper that provides malicious actors the means to install and execute other malware and tools such as Cobalt Strike, DarkSide, and Ryuk. In addition, it has other capabilities, such as the ability to provide remote access to attackers and install plug-ins for additional routines.
Zloader has multiple delivery methods, such as via email campaigns or downloads by other malware and hacking tools. One of the most basic yet reliable methods for individuals and organizations to avoid being infected by Zloader and other malware with similar arrival techniques is to apply security best practices to their emails. This includes avoiding downloading attachments or selecting links from emails that look suspicious or appear to be out of context.
Zloader’s versatility has made it a popular and effective campaign tool for any threat actor that is willing to pay for it. We already witnessed this in past campaigns — some of which took advantage of current events such as the Covid-19 pandemic — and we can expect to see it again in future campaigns from other threat actors.
Organizations can mitigate the impact of Zloader by employing robust security solutions and services. Trend Micro’s robust native XDR capabilities are tied together by Trend Micro Vision One™, which connects email, endpoints, servers, cloud workloads, and networks in order to provide a better context and perspective of the entire chain of events of an attack, while also allowing security personnel to investigate and act from a single place.
Furthermore, managed security services, such as Trend Micro™ Managed XDR, provides expert threat monitoring, correlation, and analysis from experienced cybersecurity professionals via a single and capable source of detection, analysis, and response. This expertise is further bolstered by AI-optimized, Trend Micro solutions that draw from global threat intelligence.
Zloader uses the following tactics and techniques, as mapped out according to the MITRE ATT&CK Matrix.
|Tactic||MITRE ID and Technique||Details|
|Initial Access||T1189 - Drive-by Compromise||Zloader can be downloaded through drive-by compromise via Malsmoke, RIG Exploit Kit, and Spelevo|
|T1566 - Phishing||Zloader can arrive via phishing emails with attached XLS downloader files|
|Execution||T1204 - User Execution||User can execute the XLS Zloader downloader file manually|
|T1059 -Command and Scripting Interpreter|
|T1106 - Native API||Zloader hooks native API from user32.dll and ntdll.dll to redirect execution to Zloader DLL|
|Persistence||T1060 - Registry Run Keys/Startup Folder||Creates persistence using the following registry: HKCU\SOFTWARE\Microsoft\ Windows\CurrentVersion\Run|
|T1547- Boot or Logon Autostart Execution|
|Privilege Escalation||T1055 - Process Injection||Zloader injects its loader or core component to msiexec.exe|
|Defense Evasion||T1027 - Obfuscated files or information||Instead of presenting arithmetic functions in a standardized manner and directly hardcoding constants, Zloader tries to confuse the analyst by obfuscating these in a form of various, dedicated functions|
|T1140 – Deobfuscate/ Decode Files or Information||Zloader performs XOR to decode obfuscated strings and information|
|T1497 - Virtualization/ Sandbox Evasion||Zloader downloader scripts check if it is running in a virtual environment and will not execute properly if it is|
|Credential Access||T1056 - Input Capture||Zloader captures keystrokes on browsers|
|T1539 - Steal Web Session Cookie||Zloader steals cookies from Chrome, Firefox, and Internet Explorer|
|Discovery||T1083 - File and Directory Discovery||Zloader steals cookies by discovering files from specific directories like \Mozilla\Firefox\Profiles|
|T1012 - Query Registry|
|Collection||T1185 - Man in the Browser||Zloader has to install its own (fake) certificate, and has to run a local proxy before deploying a Man-In-TheBrowser (MITB) attack|
|T1179 - Hooking|
|Command & Control||T1001 - Data Obfuscation||C2 is encrypted via RC4 and XORing algorithm where each character of the string is XORed with the preceding character which was already XORed|
|T1090 - Proxy||Zloader components injected into browsers are responsible for redirecting traffic via proxy|
|T1071- Application Layer Protocol||The following commands are accepted:|
user_execute - download an executable into the %TEMP% folder and run it (optionally with parameters)
user_cookies_get - steal cookies from all known browsers
user_url_block - block URL access for the current user
bot_uninstall - complete removal of the bot from the current user
user_password_get – steal passwords from targeted browsers
user_files_get – search and upload documents of the victims (.txt, docx,, .xls, .wallet.dat)
|T1219 - Remote Access Software||Zloader downloads and executes VNC tool to control victim machine|
|Exfiltration||T1041 - Exfiltration Over C&C Channel||Data collected by Zloader, such as stolen cookies, screenshot, and process list, are exfiltrated to C&C server|
The IOCs for Zloader can be found in this appendix.
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