Pierluigi Paganini
September 07, 2016
Ransomware is considered by the security experts one of the most dangerous threats to Internet users and organizations across the world.
Malware authors are developing new malicious codes that implement new features to improve evasion and spreading abilities.
Security researchers at BleepingComputer have reported a new ransomware dubbed Cry or CSTO because it pretends to come from the inexistent organization Central Security Treatment Organization.
The CSTO ransomware was first spotted by the malware researcher MalwareHunterTeam.
Once infected a machine the CSTO ransomware encrypts files and append the .cry extension to them. Like the Cerber ransomware, also the CSTO sends information to its command and control server via UDP.
After infecting a computer, the CSTO ransomware collects information on the host (Windows version, installed service pack, OS version, username, computer name, and CPU type) that sends via UDP to 4096 different IP addresses, but only one of them is the C&C server.
The Vxers have chosen the UDP protocol in an attempt to hide the location of the C&C server.
The threat requests the payment of a 1.1 Bitcoins (more than $600) ransom in order to decrypt the files.
The CSTO ransomware implements a singular feature, it leverages websites such as Imgur.com and Pastee.org to host information about victims, it is able to query the Google Maps API to discover the victim’s location using SSIDs of nearby wireless networks .
The ransomware uses the WlanGetNetworkBssList function to get the nearby SSIDs, in this way it is able to determine the victim’s location, but it is not clear how the malware uses this information.
“Furthermore, it will also use public sites such as Imgur.com and Pastee.org to host information about each of the victims. Last, but not least, it will query the Google Maps API to determine the victim’s location using nearby wireless SSIDs.” reported bleepingcomputer.com.
The threat encrypts the file, it uploads host information along with a list of encrypted files to Imgur.com by compiling all details in a fake PNG image file and sending it to a certain album.
Imgur, in turn, assigns a unique name for the image file and notifies it to the CSTO ransomware and then broadcasts the filename over UDP to inform the C&C server.
Similar to other ransomware, the Cry ransomware deletes the Shadow Volume Copies using the command vssadmin delete shadows /all /quiet. In this way it prevents victims from restoring the encrypted files.
The threat gains the persistency by creating a randomly named scheduled task that is triggered every time the user logs into Windows. The task also drops ransom notes on the desktop of the infected machine.
The ransom note includes instructions on how to access the Tor network to reach the payment site used by the authors.
“The ransom notes created by the Central Security Treatment Organization Ransomware contain links to a TOR payment site that has a Window title of User Cabinet. When a user visits this site, they will be prompted to login using the personal code from their ransom note.” continues bleepingcomputer.com.
The payment site includes a support page and offers victims the possibility to decryption just one file for free as proof that it is possible to decrypt all the locked files.
The researchers tested the free decryption feature, but it failed, another good reason to avoid paying the ransom.
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(Security Affairs – CSTO ransomware, cybercrime)
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