A group of Linux Trojans designed to carry out DDoS attacks. These Trojans can infect 32-bit (Linux.DnsAmp.1) and 64-bit (Linux.DnsAmp.2) versions of Linux.
Once this Trojan is launched, it automatically registers itself in the OS autorun list by modifying the etc/rc.d/rc.local file. Then the Trojan creates two threads. Though each of these threads executes the same actions, they employ different command and control servers for their work.
Once the connection to the command and control server is established, the Trojan starts gathering information about the infected system. This information can include the following data:
- OS name and version
- Free memory and Swap cache space
- CPU frequency
- Data from the dosset.dtdb file (the data is written in the file after a corresponding command is received from the command and control server)
The data acquired by the Trojan is forwarded to the remote command and control server. Then the malware awaits further commands. If the Trojan cannot receive a command, it gathers additional information and sends it to the command and control server.
Depending on the command key value (DWORD values at zero offset), the malicious program can execute the following actions:
| Key | Command |
|---|---|
| 0x99 | Set the flag of the DDoS attack’s beginning to zero. |
| 0x4DE | Save the command data to the dosset.dtdb file. |
| 0x88 | Ignore the command. |
| Other options if key < 0x5DD | If the flag of the DDoS attack’s beginning is set to zero, launch the attack. |
| 0x5DD | Restart execution of actions once the command and control server address is determined |
| (key > 0x5DD) && (key != 0xFF1) | |
| && (key != 0x99999) && (key != 0x6AF) | Update itself. |
| 0xFF1 | Terminate the work. |
The Trojan can update itself once the corresponding command is received from the server. During update, the killall <module name> command is called. As a result, the module is deleted and the wget utility is run—with its help, the updated module is downloaded to the /home directory. If the download is successful, the file becomes executable (chmod +x). Next, the downloaded file is launched.
A DDoS attack command looks as follows:
| Offset | Meaning |
|---|---|
| 76 | Victim’s IP or domain (C string) |
| 48 | Number of threads used for the attack |
| 40 | Attack type |
Trojans belonging to this group can launch the following attacks:
- SYN Flood (repetitive sending of a specially generated package to the attacked host until the host stops responding)
- UDP Flood (after establishing a connection to the attacked host over the UDP protocol, the Trojan attempts to send the victim 1,000 messages)
- Ping Flood (an echo request with the process PID as an identifier is generated over the ICMP protocol (data is the HEX value 0xA1B0A1B0))
- Sending requests to DNS servers (DNS Amplification)
- Sending requests to NTP servers (NTP Amplification—implemented, but not used, in older versions of these Trojans)
