Thanks to reader Gary for sending us in a sample of a *Coin miner that he found attacking Port 32764. Port 32764 was recently found to offer yet another backdoor on Sercomm equipped devices. We covered this backdoor before [1]

The bot itself appears to be a variant of the "zollard" worm sean before by Symantec [2]. Symantec's writeup describes the worm as attacking a php-cgi vulnerability, not the Sercomm backdoor. But this worm has been seen using various exploits.

Here some quick, very preliminary, details:

The reason I call it *Coin vs. Bitcoin is that in the past, we found these miners to mostly attack non-Bitcoin crypto-currencies to make use of the limited capabilities of these devices. I do not have sufficient detail yet about this variant.

Interestingly, Gary found what looks like 5 binaries with identical functionality, but compiled for 4 different architecture providing for larger coverage across possible vulnerable devices. The binaries are named according to the architecture they support.

The binary appears to do the following among other things:

• delete and then recreate the /tmp directory (to have an empty one for download)
• create a directory /var/run/.zollard
• firewall port 23 (telnet) and 32764 (trying to avoid re-exploitation. Port 23 is odd ...)
• start the telnet demon (odd that it also firewalls port 23)
• it uses this user agent for some outbound requests: Mozilla/5.0 (compatible; Zollard; Linux)
• setup a php file with a backdoor (simple php "exec") 

It also looks like there are many other variants for different architectures based on string in the file Gary sent us.

[1] https://isc.sans.edu/diary/Port+32764+Router+Backdoor+is+Back+(or+was+it+ever+gone%3F)/18009
[2] http://www.symantec.com/connect/blogs/linux-worm-targeting-hidden-devices

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Johannes B. Ullrich, Ph.D.
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