Attackers Use Trojanized Version of PuTTY to Steal SSH Credentials

Malicious actors are using a trojanized version of PuTTY, the popular open-source Secure Shell (SSH) and telnet client, to gain access to remote computers and steal valuable data, Symantec warned on Monday.

According to experts, the attackers created the malicious PuTTY back in late 2013, when they uploaded a sample to VirusTotal. Symantec says this trojanized version disappeared until recently.

Cybercriminals are distributing the malware by hijacking websites that appear in search engine results when users look for PuTTY. When users access the compromised site, they are taken through several redirects to a website hosted in the United Arab Emirates that is set up to serve the fake version.

“Our telemetry reveals that the current distribution of the Trojanized version of PuTTY is not widespread and is not specific to one region or industry,” Symantec said in a blog post.

When users initiate an SSH connection in order to securely access a remote server, the connection URL includes the server’s address, the port number, the username, and the password. The trojanized version of PuTTY is designed to copy this URL, encode it, and send it back to a server controlled by the attackers.

“Attackers can ultimately use this sensitive information to get the highest level of privileges on a computer or server, (known as “root” access) which can give them complete control over the targeted system,” experts said.

The trojanized PuTTY is detected by Symantec products as Hacktool, WS.Reputation.1, and Suspicious.Cloud.9. Experts noted that the rogue variant is much larger in size than the legitimate one.

Since PuTTY is commonly used by system and database administrators, and web developers to access remote servers, the tool is often whitelisted and it’s not viewed as a threat by firewalls and security products. This makes the malware spotted by Symantec even more dangerous.

This isn’t the first time this particular malicious actor launches a trojanized version of a popular application in an effort to steal sensitive information. In January 2014, Avast reported spotting a malicious variant of the FileZilla FTP client that was designed to harvest login details and send them to a remote server located in Germany.