From March to July this year, the ThreatRecon team noticed a spear phishing campaign by the SectorE02 group going on against the Government of Pakistan and organizations there related to defense and intelligence. Spear phishing emails are sent to their victims via Excel XLS files, which asks their victims to enable macros which will end up executing the downloader. Malicious document lures they have employed in recent times include a document purporting to be for registration for the Pakistan Air Force.
SectorE02 is a threat actor which targets countries in South Asia, especially Pakistan, since at least 2012. Their arsenal includes a modular framework researchers have dubbed the “YTY Framework”, which has a Windows and mobile version. Usage of this framework allows the SectorE02 group to constantly modify and even remake individual plugins of the framework, and pick and choose which plugins – if any – are sent to their victims. This modularity also allows the SectorE02 group to maintain low detections by antivirus engines because each module only does something simple and will not even work without certain previously dropped files. In this post, we will describe their lure document, first stage downloader, file plugin, screenshot plugin, keylogger plugin, and exfiltration uploader plugin.
Excel Spear Phishing
The excel file used by them had names such as Credit_Score.xls, Advance_Salary.xls, CSD_Schemes_2019.xls, and Agrani_Bank.xls. In some instances, it masqueraded as an Excel calculator from the National Bank of Pakistan.
In later stages of the campaign, however, the group appeared to switch to using a MsgBox to show an error saying “This file is corrupted”.
At the back, the excel macro would retrieve encoded data stored in itself, and the encoding here is just a simple decimal encoding with a comma (or exclamation mark) as a separator. The same encoding is used for the dropped executable, although more often one entire file is encoded as a zip archive containing two files – a batch script and executable which is then unzipped and executed.
The dropped batch scripts follow the same basic format: creating folders with the hidden, system, and archive attributes, dropping the batch and executable files there, and setting persistence through either scheduled tasks or the autorun registry key. A text file containing the %COMPUTERNAME% variable and random digits will also be saved as “win.txt”, and this file is required for the executable downloader.
The batch file that is dropped is used for three main purposes: 1) to set up the first folder, which is used to store the text file containing the computer name, 2) to set up what we call the “common exfiltration folder” which each individual plugin uses for different purposes, and 3) to set up persistence via scheduled task or registry run keys.
Looking at the latest downloader executable which masquerades its filename as an InPage word document (bgfRdstr54sf.inp), it starts off by using CreateEventA as a mutex with the value “ab567” and only works if the file %USERPROFILE%\DriveData\Files\win.txt exists. It polls the C2 server every 100 or so seconds. It uses the fixed user agent string “Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Firefox/52.0”, and performs a HTTPS GET against servicejobs[.]life/orderme/<computername>-<random>.
This is a change from their previous URL structure, “/orderme”, which contained the file(s) to be downloaded, and this allows them to cherry pick their victims – unless the SectorE02 operator specifically places the next stage malware in the server directory for a particular victim, that victim will only ever be infected with the downloader.
The downloader malware accepts three commands from the server, when the Content-Type response is “Content-Type: application”, “Content-Type: cmdline”, or “Content-Type: batcmd”, which are used for saving files to disk or executing files/commands on the system. This is how the next stage downloader or plugins can be executed on the victim system.
Screenshot Plugin (f10f41bd38832596d4c449f81b9eb4129361aa4e4ebd4a8e8d2d8bf388934ca5)
This executable plugin takes a screenshot every two minutes using the Windows API to draw the raw screen bitmap to the common exfiltration folder, %USERPROFILE%\Print\Network\Server\. It then converts this raw bitmap to a JPG in a new file and deletes the raw bitmap file.
The screenshot files are named in the format of “tm_hour-tm_min-tm_sec-tm_year-tm_mday-tm_mon” .
Like some of the other YTY components, the obfuscated strings can be deobfuscated by running both the base64 and reverse string algorithm multiple (in this case, three) times.
File Listing Plugin (d71a1d993e9515ec69a32f913c2a18f14cdb52ef06e4011c8622b5945440c1aa)
This executable plugin recursively searches through the “C:”, “D:”, “E:”, “F:”, “G:”, and “H:” drives, looking for interesting file extensions shown below. Several default folders are avoided by the malware.
Note that the “.inp” extension is for “Urdu InPage”, a word processing program which supports languages such as Urdu which is the national language of Pakistan. The extensions the 2019 version of this plugin did not previously look for are “.odt” and “.eml”, and “.rft” is just a spelling mistake they made of “.rtf”.
It only looks for files modified later than year 2017 and saves the text data of all matching files found in %APPDATA%\DriveData\Files\clist.log using the format of “File Path|Size WriteTimestamp l_flag”.
A copy of these matching files are also saved to the common exfiltration folder, %USERPROFILE%\Print\Network\Server\. The copied files are individually saved with the file names being the full file path to the copied file, with slashes becoming underscores.
Keylogger Plugin (f331f67baa2650c426daae9dee6066029beb8b17253f26ad9ebbd3a64b2b6a37)
This plugin starts off by using CreateEventA as a mutex with the value “k4351”. It saves user keystrokes and which window title those keystrokes were pressed in the common exfiltration folder, %USERPROFILE%\Print\Network\Server\. The file is saved as “<username>_YYYY_MM_DD(HH_mm_ss).txt”.
Uploader Plugin (d4e587b16fbc486a62cc33febd5438be3a9690afc1650af702ed42d00ebfd39e)
This plugin starts off by using CreateEventA as a mutex with the value “MyEvent3525” and only works if the file %USERPROFILE%\DriveData\Files\win.txt exists . While the other plugins dump their files into the common exfiltration folder, the uploader plugin takes the files from that folder and uploads it to the C2 server, which is the same server as the downloader C2 server. The uploaded files are deleted immediately after.
The uploader performs a HTTP POST to /upload/<computername> of the file using HTTP forms with the same hard coded user-agent as their downloader malware, “Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Firefox/52.0”.
While the use of a modular framework is not a new concept, we see that the SectorE02 group’s continuous remaking of their YTY framework plugins which serve the same purpose allows them to keep detections by security tools at a minimum. Based on their campaigns and the plugins we have seen, we believe they may be recreating each plugin on a per-campaign basis, meaning that each attack campaign might be targeting with new binaries coded from scratch and be hardly detected by security tools. At the same time, their newfound cautiousness in protecting their binaries from being downloaded and limited targeting means that the hardest part of detecting and responding to the SectorE02 group may be finding their related binaries in the first place.
Indicators of Compromise
Malicious Excel Files (SHA-256)
Dropped Batch Scripts (SHA-256)
Dropped YTY Downloaders (SHA-256)
YTY File Plugin
YTY Screenshot Plugin
YTY Keylogger Plugin
YTY File Exfiltration Uploader Plugin
MITRE ATT&CK Techniques
The following is a list of MITRE ATT&CK Techniques we have observed based on our analysis of these malware.
T1193 Spearphishing Attachment
T1059 Command-Line Interface
T1053 Scheduled Task
T1204 User Execution
T1158 Hidden Files and Directories
T1060 Registry Run Keys / Startup Folder
T1053 Scheduled Task
T1140 Deobfuscate/Decode Files or Information
T1107 File Deletion
T1158 Hidden Files and Directories
T1066 Indicator Removal from Tools
T1112 Modify Registry
T1027 Obfuscated Files or Information
T1056 Input Capture
T1010 Application Window Discovery
T1083 File and Directory Discovery
T1082 System Information Discovery
T1497 Virtualization/Sandbox Evasion
T1119 Automated Collection
T1005 Data from Local System
T1039 Data from Network Shared Drive
T1025 Data from Removable Media
T1074 Data Staged
T1114 Email Collection
T1056 Input Capture
T1113 Screen Capture
Command and Control
T1043 Commonly Used Port
T1071 Standard Application Layer Protocol
T1020 Automated Exfiltration
T1041 Exfiltration Over Command and Control Channel
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