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Tuesday, 27 November 2018 08:44

Linux malware of no use unless it gains access through SSH

Linux malware of no use unless it gains access through SSH Pixabay

A script that mines for cryptocurrencies on Linux systems first needs to infect these systems, either by using brute force to guess SSH passwords or else by gaining entry through the use of stolen credentials that can be bought on dark web forums.

Security researcher Alexander Vurasko, who runs the Dr Web anti-virus firm, told iTWire in response to queries that the malware itself — which he has named Linux.BtcMine.174 — was a long and complicated script that could do a number of things, including upping its privileges if the system was still vulnerable to a two-year-old flaw known as the Dirty Cow vulnerability.

The malware has been reported by some without offering any perspective as to how it first gains entry to a system, with a bid to apparently portray it as a weakness in Linux itself.

Asked about how the malware could gain access to systems, Vurasko responded, "In the first place it works like this: somebody searches for servers with [the] SSH port open; he is trying to brute [force] servers he found; if the brute force attack was successful, he connects to the compromised server using brute-forced credentials and starts the malware."

He added that brute-forced and stolen credentials were widely available for sale on hacker forums.

"Therefore, you don't have to brute [force] servers, You can buy credentials and install malware for mining via SSH."

Varusko said the malware could also gain entry to a Linux box by using credentials saved on the local drive of an infected system and spread like a worm. But, he added, for this it "surely must have a lot of luck to find saved logins and passwords to SSH sessions".

Once an attacker managed to gain access through SSH, then another vulnerability, which affected kernels from 2.6.37 to 3.8.8, could be exploited to raise the privileges of the attacker.

The mining script was then downloaded from another server. After that a trojan was downloaded and this could be used to stage DDoS attacks.

A third component downloaded was a rootkit that was able to steal passwords which are entered for the su command and hide them.

The mining script was then started and used to mine for monero.

But nothing of this is possible, unless an attacker manages to first gain access to a Linux box through SSH. Which means that weak passwords are a security risk, something that is rather widely known.


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Sam Varghese

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Sam Varghese has been writing for iTWire since 2006, a year after the site came into existence. For nearly a decade thereafter, he wrote mostly about free and open source software, based on his own use of this genre of software. Since May 2016, he has been writing across many areas of technology. He has been a journalist for nearly 40 years in India (Indian Express and Deccan Herald), the UAE (Khaleej Times) and Australia (Daily Commercial News (now defunct) and The Age). His personal blog is titled Irregular Expression.



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