Background
On May 27, 2019, Our Unknown Threat Detect System highlighted a suspicious ELF file, and till this day, the detection rate on VT is still only one with a very generic name. We determined that this is a Proxy Botnet, and it is a Linux version variant of the Win32.Ngioweb[1] malware. We named it Linux.Ngioweb. It shares a lot of code with Win32.Ngioweb, except that it has DGA features. We registered one of the DGA C2 domain names (enutofish-pronadimoful-multihitision.org) and was able to observe the Bot connections.
In addition, we have observed that Linux.Ngioweb malware has been implanted into a large number of WordPress Web servers.
Although the Bot program is loaded with the privilege of the user group corresponding to the Web container, it still works and runs as Rotating Proxy node[2].
We don’t know why the attacker runs this proxy botnet, but it is possible that everything goes through the proxy is being recorded by the attacker.
Overview of Linux.Ngioweb
The main functionality of the Linux.Ngioweb Bot sample is to implement Back-Connect Proxy[3].on the victim’s machine. The attacker builds multiple Bots into a Proxies Pool and controls it through a two-tier C2 protocol, then provides a Rotating Proxy Service.
Reverse engineering on Linux.Ngioweb
Basic information
- MD5: 827ecf99001fa66de513fe5281ce064d
ELF 64-bit LSB executable, AMD x86-64, version 1 (SYSV), statically linked, stripped
Anti-reverse engineering technique
Uses a niche library named musl libc
Stores its functions in the function table in advance
Uses Stack Strings Obfuscation
Generates constant table used by CRC and AES
Uses a two-tier C2 protocol, where Stage-2 C2 is determined by the CONNECT instruction of Stage-1 C2
Stage-2 C2 uses a two-layer encrypted communication protocol
Stage-1 C2 protocol analysis
At this stage, the main behavior of the sample is to establish communication with Stage-1 C2, and proceed to the next step according to the instructions returned by C2.
Communication attempt
Try to establish communication with the following hardcoded C2 IP every 60 seconds
169.239.128.166:443
185.244.149.73:443Try to establish communication with the domain name generated by DGA (Domain Generation Algorithm) every 73 seconds. When the number of DGA domain names reaches 300, the Seed will be reset. So the total number of DGA domain names is 300.
DGA implementation
uint64_t GenSeed(uint32_t& seed, uint32_t mod) { uint32_t tmp = 0x41C64E6D * seed + 0x3039; seed = tmp; return tmp % mod; } string dga(uint32_t& seed) { char* HeadBuf[] = { "un", "under", "re", "in", "im", "il", "ir", "en", "em", "over", "mis", "dis", "pre", "post", "anti","inter", "sub", "ultra", "non", "de","pro", "trans", "ex", "macro", "micro", "mini","mono", "multi", "semi", "co" }; char* BodyBufA[] = {"able","ant","ate","age","ance","ancy","an","ary", "al","en","ency","er","etn", "ed", "ese","ern","ize", "ify","ing","ish","ity","ion","ian","ism","ist","ic","ical", "ible","ive","ite","ish","ian","or","ous","ure" }; char* BodyBufB[] = {"dom","hood","less","like","ly","fy","ful","ness", "ment","sion","ssion","ship","ty","th","tion","ward" }; char* TailBuf[] = { ".net",".info",".com",".biz",".org",".name" }; string BlockBufA = "aeiou"; string BlockBufB = "bcdfghklmnprstvxz"; string domain; uint32_t dashloop = GenSeed(seed, 3) + 1; while (dashloop--) { domain += HeadBuf[GenSeed(seed, 0x1e)]; int flag = 0; int i = 0; if (BlockBufA.find(domain.back()) == string::npos) flag = 1; int fillcnt = GenSeed(seed, 0x3) + 4; while (fillcnt > i) { if (flag + i & 1) domain += BlockBufA[GenSeed(seed, 0x5)]; else domain += BlockBufB[GenSeed(seed, 0x11)]; i++; } if (BlockBufA.find(domain.back()) == string::npos) domain += BodyBufA[GenSeed(seed, 0x23)]; else domain += BodyBufB[GenSeed(seed, 0x10)]; if (dashloop != 0) domain += "-"; } return domain += TailBuf[GenSeed(seed, 0x6)]; } Communication Protocol
This phase of communication is based on the HTTP protocol and the parameters are Base64 encoded.
Packets overview
Sent Packets decode
After decoded the parameter content by Base64, we get the following information.
id=machine-id[0:15]
v=x86_64, hardcoded, architecture
sv=5003, hardcoded, version number
&qlohmzalwdepupwf, random 16-byte data, the algorithm is as follows
User-Agent, hardcoded
Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:59.0) Gecko/20100101 Firefox/59.0
Received Packets decode
Command Supported
- WAIT
- CONNECT
- DISCONNECT
- CERT
Stage-2 C2 protocol analysis
At this stage, the main action of the sample is to establish communication with the C2 of Stage-2 and enable the Back-Connect Proxy function. C2 of stage-2 is specified by the CONNECT command.
Communication Protocol
At this stage, the communication is combined by double-layer encryption. The inner layer is XOR and the outer layer is AES.
Packets overview
Encryption Algorithm
The XOR key is generated by a random algorithm:
The algorithm is:
AES uses ECB mode, no padding. The key is:qwerasdfzxcqwerasdftyuirfdsdsdss
Packet Structure
The packet consists of two parts: “header” and “msg”.
“header” structure:
#le->little endian #be->big endian struct header { uint32_le xorkey; uint32_be msgcrc32; uint32_be len; uint16_be msgcode uint16_be magic }; “msg” consists of chunks, and the chunks supported by the sample are as follows:
| Chunk Type | Chunk Length | Description |
|---|---|---|
| 1 | 1 | BYTE |
| 2 | 2 | WORD big endian |
| 3 | 4 | DWORD big endian |
| 4 | 8 | QWORD big endian |
| 5 | N+4 | Bytes array.The first 4 bytes of chunk are the big endian-encoded length (N) of the array |
A “msg” can have one or more chunks, and different “msg”s are made up by different chunks .
The “msg” types uses by this sample are “recv” and “send”.
recv
send
See the table below for a summary of different “msg”s:
| msgcode | Driection | Description | Fromat |
|---|---|---|---|
| 0x1010 | recv | set channel id | 3 chunks:(QWORD ConnId, Array IPAddr,WORD Port) |
| 0x1011 | recv | start proxy request | 5 chunks:(QWORD RequestId, BYTE reason,BYTE AddrType,Array Addr, WORD port) |
| 0x1012 | recv | close connection | 1 chunk:(QWORD ConnId) |
| 0x10 | send | check-in | 1 chunk:(QWORD BotId) |
| 0x11 | send | set-channel ack | 1 chunk:(DWORD VersionId) |
| 0x14 | send | tcp server started | 5 chunks:(DWORD ConnectionId, QWORD RequestId, BYTE AddrType, Array Addr, WORD Port) |
| 0x15 | send | error | 2 chunks:(DWORD RequestId,BYTE reason ) |
| 0x16 | send | udp server started | 5 chunks:(DWORD ConnectionId, QWORD RequestId, BYTE AddrType, Array Addr, WORD Port) |
Sent packets sample analysis
Raw data
packet[0:31]: 6c 52 8c 08 3e 80 a9 3c 00 00 00 10 00 10 fa 51 04 dd b0 b4 9d 10 ec 42 c3 00 00 00 00 00 00 00 header --->packet[0:15] xorkey --->0x088c526c msgcrc32 --->0x3e80a93c msglen --->0x00000010 msgcode --->0x0010,check-in magic --->0xfa51 msg --->packet[16:31] 1st chunk chunktype --->0x4 content --->0xddb0b49d10ec42c3After XOR encryption
6c 52 8c 08 36 0c fb 50 08 8c 52 7c 08 9c a8 3d 0c 51 e2 d8 95 9c be 2e cb 8c 52 6c 08 8c 52 6cAfter AES encryption
c1 d3 78 71 2d f6 5b bb 16 ca ff 8b ef 69 bb 26 3b 01 f0 22 70 09 38 dc e7 06 89 de 2b 55 eb 8e
Received packets sample analysis
Raw data
c5 ad 4a bf 30 C2 3a 43 9b 6e 22 08 73 e0 b9 5d 3c e6 b7 f0 74 76 53 43 3a 79 0e 82 80 1a c3 84 ba a4 85 05 4a 63 b1 d6 d1 94 ad 53 be 7a 9a 88After AES decryption
59 8b e5 6d 4a ee bf ef 6d e5 8b 79 7d f5 71 08 69 b8 81 aa 92 ed 65 fb 29 e0 8b 59 6d e1 51 47 19 e1 89 d8 29 e5 8b 59 6d e5 8b 59 6d e5 8b 59After XOR decryption
packet[0:47] 59 8b e5 6d 27 0b 34 b6 00 00 00 20 10 10 fa 51 04 5d 0a f3 ff 08 ee a2 44 05 00 00 00 04 da 1e 74 04 02 81 44 00 00 00 00 00 00 00 00 00 00 00 header --->packet[0:15] xorkey --->0x6de58b59 msgcrc32 --->0x270b34b6 msglen --->0x00000020 msgcode --->0x1010,set channel id magic --->0xfa51 msg --->packet[16:47] 1st chunk chunktype --->0x04 content --->0x5d0af3ff08eea244 2nt chunk chunktype --->0x05 content --->len:0x00000004 buf:0xda1e7404 3rd chunk chunktype --->0x02 content --->0x8144
Stage-2 C2 association analysis
We obtained the following 6 Stage-2 C2 addresses by visiting the Stage-1 C2 URL (http://185.244.149.73:443/min.js).
5.135.58.119 5.135.58.121 5.135.58.123 5.135.58.124 91.134.157.11 193.70.73.115 We looked up this md5 (9017804333c820e3b4249130fc989e00) in our GraphicQuery platform and was able to find more IPs which host the same file, we then sent specific crafted packets to these IPs and was able to ID another 18 Stage-2 C2s.
5.135.35.160 5.196.194.209 51.254.57.83 54.36.244.84 54.36.244.85 54.36.244.91 91.121.36.212 91.121.236.219 92.222.151.63 145.239.108.241 163.172.201.184 163.172.202.116 178.33.101.176 178.33.101.177 178.33.101.178 178.33.101.182 188.165.5.123 188.165.163.20 We found that these Stage-2 C2 IP address are providing Socks5 proxy service by looking them up on free-socks.in
As we tested, all these Socks5 proxy IPs are properly functioning. Also, they accessed the C2 domain we own(enutofish-pronadimoful-multihitision.org) via the Stage-1 C2 protocol, so it can be said that they are all Linux.Ngioweb Bots.
root@localhost:~# curl --socks5 91.134.157.11:50880 ifconfig.me 31.170.123.49 root@localhost:~# curl --socks5 91.134.157.11:62012 ifconfig.me 208.113.197.88 root@localhost:~# curl --socks5 91.134.157.11:18278 ifconfig.me 45.58.190.100 root@localhost:~# curl --socks5 91.134.157.11:64380 ifconfig.me 72.29.64.29 root@localhost:~# curl --socks5 91.134.157.11:47067 ifconfig.me 54.38.101.17 root@localhost:~# curl --socks5 91.134.157.11:63862 ifconfig.me 88.99.212.97 root@localhost:~# curl --socks5 91.134.157.11:49475 ifconfig.me 23.91.65.240 Infected IPs information
By listening on C2 domain (enutofish-pronadimoful-multihitision.org), we have observed a total of 2692 Bot IPs.
The following is a detailed list of countries/regions with number of infected IPs:
US 1306 BR 156 RU 152 DE 133 FR 102 SG 98 NL 80 GB 66 CA 66 IT 64 VN 42 AU 36 PL 31 TR 28 JP 26 IN 26 ZA 21 ID 19 ES 18 UA 15 By probing the infected IPs, we found out that almost all Bot IPs are web servers and have WordPress programs deployed. We did not look into how the attacker took control of these WordPress sites though.
We contacted some infected users and found multiple WebShells on their Web servers.
These WebShells are highly obscured, but the techniques, encryption, and code share similar characters.
Combined with the accessing characteristics (such as time, order) the infected IPs made to the our sinkhole DGA domain, we speculate that the attacker will periodically issue commands to the WebShells on the victim websites, as well as running the Linux.Ngioweb program.
Solutions and Suggestions
We recommend that readers do not use the Socks5 proxy service provided by these Stage-2 C2 IP.
We recommend that WordPress users back up the website article database (delete backdoor users such as wp.service.controller.*), reinstall the latest version of WordPress program, enhance user password complexity, enhance WebShell detection capabilities, and disable PHP commands to execute related functions;
Contact us
Relevant security and law enforcement agencies are welcomed to contact netlab[at]360.cn for a list of infected IP addresses.
Readers are always welcomed to reach us on twitter, WeChat 360Netlab or email to netlab at 360 dot cn.
IoC list
Sample MD5
827ecf99001fa66de513fe5281ce064d Stage-1 C2 (Hardcoded IP)
169.239.128.166 South Africa ASN 61138 Zappie Host LLC 185.244.149.73 Romania ASN 60117 Host Sailor Ltd. Stage-2 C2
163.172.201.184 France ASN 12876 Online S.a.s. 163.172.202.116 France ASN 12876 Online S.a.s. 5.135.35.160 France ASN 16276 OVH SAS 5.135.58.119 France ASN 16276 OVH SAS 5.135.58.121 France ASN 16276 OVH SAS 5.135.58.123 France ASN 16276 OVH SAS 5.135.58.124 France ASN 16276 OVH SAS 5.196.194.209 France ASN 16276 OVH SAS 51.254.57.83 France ASN 16276 OVH SAS 54.36.244.84 France ASN 16276 OVH SAS 54.36.244.85 France ASN 16276 OVH SAS 54.36.244.91 France ASN 16276 OVH SAS 91.121.36.212 France ASN 16276 OVH SAS 91.121.236.219 France ASN 16276 OVH SAS 91.134.157.11 France ASN 16276 OVH SAS 92.222.151.63 France ASN 16276 OVH SAS 145.239.108.241 Germany ASN 16276 OVH SAS 178.33.101.176 Ireland ASN 16276 OVH SAS 178.33.101.177 Ireland ASN 16276 OVH SAS 178.33.101.178 Ireland ASN 16276 OVH SAS 178.33.101.182 Ireland ASN 16276 OVH SAS 188.165.5.123 Ireland ASN 16276 OVH SAS 188.165.163.20 France ASN 16276 OVH SAS 193.70.73.115 France ASN 16276 OVH SAS Stage-1 C2 (DGA)
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