Threat Level: green Handler on Duty: Didier Stevens

SANS ISC: Multi Platform *Coin Miner Attacking Routers on Port 32764 SANS ISC InfoSec Forums

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Multi Platform *Coin Miner Attacking Routers on Port 32764

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.

Name Size "file" output
arm 86680 ELF 32-bit LSB executable, ARM, version 1, statically linked, stripped
armeabi 131812 ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, stripped
mips 140352 ELF 32-bit MSB executable, MIPS, MIPS-I version 1 (SYSV), statically linked, stripped
mipsel 141288 ELF 32-bit LSB executable, MIPS, MIPS-I version 1 (SYSV), statically linked, stripped
x86 74332 ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically linked, stripped

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.
STI|Twitter|LinkedIn

I will be teaching next: Defending Web Applications Security Essentials - SANS San Francisco Spring 2020

Johannes

3698 Posts
ISC Handler
RE: Multi Platform *Coin Miner Attacking Routers on Port 32764

Hello,

I have an Asus RT-N66U, which I try to ensure is up to date on it's firmware and has all unnecessary or insecure features disabled.
I keep an anti virus and firewall solution up to date as well as my windows updates.

But when it comes to things like the story in this diary. How does an end user like myself determine if something malicious is happening on my
router?

I know how to enable telnet and use putty to telnet, it appears to run some form of gnu Linux but alas I am a windows user.

Any advice you can provide would be appreciated.

Sincerely

PN
Anonymous

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