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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.
A family of Linux Trojans. One of its representatives is described below.
A modified version of Linux.DDoS.87 and Linux.DDoS.89. Its main differences from Linux.DDoS.89 are as follows:
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.Mirai.3794
Linux.Mirai.3801
Linux.Mirai.3804
Linux.Mirai.3869
Linux.Mirai.3896
Linux.Mirai.3899
Linux.Mirai.3900
Linux.Mirai.3912
Linux.Mirai.3913
Linux.Mirai.3914
Linux.Mirai.3915
Linux.Mirai.3924
Linux.Mirai.3933
Linux.Mirai.3934
Linux.Mirai.3935
Linux.Mirai.3936
Linux.Mirai.3937
Linux.Mirai.3938
Linux.Mirai.3939
Linux.Mirai.3940
Linux.Mirai.3943
Linux.Mirai.3947
Linux.Mirai.3948
Linux.Mirai.3949
Linux.Mirai.3950
Linux.Mirai.3951
Linux.Mirai.3952
Linux.Mirai.3953
Linux.Mirai.3954
Linux.Mirai.3955
Linux.Mirai.3956
Linux.Mirai.3957
Linux.Mirai.3958
Linux.Mirai.3991
Linux.Mirai.4045
Linux.Mirai.4124
Linux.Mirai.4133
Linux.Mirai.4143
Linux.Mirai.4271
Linux.Mirai.4279
Linux.Mirai.4293
Linux.Mirai.4294
Linux.Mirai.4295
Linux.Mirai.4306
Linux.Mirai.4309
Linux.Mirai.4330
Linux.Mirai.4339
Linux.Mirai.4340
Linux.Mirai.4341
Linux.Mirai.4342
According to statistics, every fifth program for Android contains a vulnerability (or, in other words, a "loophole") that lets cybercriminals successfully introduce Trojans onto mobile devices and manipulate them into doing whatever actions they need them to.
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