Virus library

An analysis of the technologies used by cybercriminals allows us to draw conclusions about the virus industry’s possible vectors of development and more effectively confront future threats. You, too, can learn what actions various malicious programs take in infected systems and how to withstand them.

Linux in virus library:

A family of Linux Trojans. One of its representatives is described below.

SHA1:

7e0e07d19b9c57149e72a7ed266e0c8aa5019a6f

A modified version of Linux.DDoS.87 and Linux.DDoS.89. Its main differences from Linux.DDoS.89 are as follows:

Some samples of the Trojan can now delete themselves.
The Trojan can disable the watchdog timer, which prevents system hangs, to make it impossible to reboot the computer.
The process’s name is changed to a random sequence containing the characters [a-z 0-9].
The configuration structure has been changed.
If a process named “.anime” is found, the Runkiller function not only terminates this process but also deletes the executable file.
Unlike Linux.DDoS.89, this version can execute HTTP Flood attacks.
If the Trojan fails to create a socket and connect to it, the corresponding function searches for the process that owns the socket and kills it.

The Trojan’s configuration looks as follows:

Number	Value	Purpose
3	listening tun0	main output to stdin
4	Host	Command and control (C&C) server’s IP address
5	Port	C&C server’s port
6	"https://youtube.com/watch?v=dQw4w9WgXcQ"
7	"/proc/"	runkiller
8	"/exe"	runkiller
9	" (deleted)"
10	"/fd"	runkiller
11	".anime"	runkiller
12	"REPORT %s:%s"	runkiller
13	"HTTPFLOOD"	runkiller
14	"LOLNOGTFO"	runkiller
15	"\x58\x4D\x4E\x4E\x43\x50\x46\x22"	runkiller
16	"zollard"	runkiller
17	"GETLOCALIP"
18	Host
19	Port
20	"shell"
21	"enable"
22	"system"
23	"sh"
24	"/bin/busybox MIRAI"
25	"MIRAI: applet not found"
26	"ncorrect"
27	"/bin/busybox ps"
28	"/bin/busybox kill -9 "
29	"TSource Engine Query"
30	"/etc/resolv.conf"
31	"nameserver"
32	"Connection: keep-alive"
33	"Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,/;q=0.8"
34	"Accept-Language: en-US,en;q=0.8"
35	"Content-Type: application/x-www-form-urlencoded"
36	"setCookie('"
37	"refresh:"
38	"location:"
39	"set-cookie:"
40	"content-length:"
41	"transfer-encoding:"
42	"chunked"
43	"keep-alive"
44	"connection:"
45	"server: dosarrest"
46	"server: cloudflare-nginx"
47	"Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36"	User Agent
48	"Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36"	User Agent
49	"Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36"	User Agent
50	"Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36"	User Agent
51	"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/601.7.7 (KHTML, like Gecko) Version/9.1.2 Safari/601.7.7"	User Agent

All samples of the Trojan use a function that hides the following strings:

def decode(str_enc):
  return "".join([chr(ord(x) ^ 0x22) for x in str_enc])

Once launched, the Trojan removes its executable file from the disk, blocks the SIGINT signal with the help of sigprocmask, and sets the parameter SIG_IGN for SIGCHLD and a handler for SIGTRAP.

Then the Trojan tries to open the /dev/watchdog file for reading/writing (/dev/misc/watchdog is also checked) and, if successful, disables the watchdog timer.

ioctl(fd, WDIOC_SETOPTION, WDIOS_DISABLECARD)

The Trojan subsequently opens a root folder and sends a request to the address 8.8.8.8:53 to get the IP address of its network traffic.

Next, the Trojan calculates a function taken from the argv[0] value:

def check(name):
    print name
    a = [ord(x) for x in name]
    sum = (0 - 0x51) & 0xff
    for i in [2,4,6,8,10,12]:
        z =  (~a[i % len(a)] & 0xff)
        sum = (sum + z)&0xff
        #print "%x %x %x" % (z, sum, sum % 9)
    return sum % 9

This function returns a number from 0 to 8 that represents an index in a function array:

off_8055DC0     dd offset bind_socket   ; DATA XREF: main+109o
.rodata:08055DC4                     dd offset sub_80517E0
.rodata:08055DC8                     dd offset sub_8051730
.rodata:08055DCC                     dd offset create_config
.rodata:08055DD0                     dd offset sub_8051760
.rodata:08055DD4                     dd offset sub_80523F0
.rodata:08055DD8                     dd offset strcopy
.rodata:08055DDC                     dd offset runkiller
.rodata:08055DE0                     dd offset sub_804E900

If argv[0] == “./dvrHelper”, a parental process receives the SIGTRAP signal (for which a handler was previously installed). The handler, in turn, modifies the IP address taken from the configuration and the C&C server’s port to which the Trojan will connect.

Then a listening socket is opened at the address 127.0.0.1:48101. If this port is busy with another process, the Trojan runs a function that finds the process and kills it.

The Trojan subsequently generates a name that looks like a random sequence containing the characters [a-z 0-9] and writes it to argv[0]. Using the prctl function, the process’s name is changed to a random one.

Next, the Trojan creates child processes and terminates the parental one. All further steps are performed in a child process—in particular, a structure containing handlers is filled in. Then a function responsible for scanning telnet nodes and a function that terminates the processes of other Trojans are launched. The Trojan then runs a handler for incoming instructions sent from the C&C server. If the Trojan detects that a connection to a local server is being established, it runs a child process to scan vulnerable telnet nodes and terminates the parental process.

The picture below shows a code fragment for Linux.DDoS.87 (left column) and Linux.Mirai (right column).

Linux aliases: