Shehriyar Qureshi
thatdevsherry's Blog

thatdevsherry's Blog

Accessing root shell of my home router

Subscribe to my newsletter and never miss my upcoming articles

Router Details

Vendor: FiberHome Telecommunication Technologies Co. Ltd

Software Version: 3.10L.02.A2pB022g.d20h

Bootloader (CFE) Version: before 1.0.37-5.12

Analyzing Attack Points

I had the following services enabled:

  • FTP
  • HTTP
  • SNMP
  • TELNET
  • TFTP

I had previously connected to FTP but the ls commands never worked so I didn't bother diving into it more.

I had no experience w/ SNMP and TFTP so my only option was to try TELNET.

Accessing Telnet

The password for FTP was the same as the default HTTP login one. What was interesting is that I had changed my HTTP login password, and that also changed the password of telnet login to the one I updated to, so my login to telnet was pretty straight forward.

Exploring Telnet

It was a typical telnet instance that I had also seen way back when I first tinkered w/ telnet on the router. It had the common telnet commands along w/ some specific ones like testing LEDs on the router, but that was not much fun.

Curiosity

There was one command in special that I liked, the ps command. I felt like the memory of the router was always on the edge, so I thought why not see what processes are running and if I can find something. The output was pretty normal, showing some dhcpd, init etc but there were some lines that caught my attention

  PID  Uid     VmSize Stat Command
   37 admin       316 S   -sh
12120 admin       280 S   sh -c ps
12121 admin       272 R   ps

So this meant some shell processes were running, and the last two ones were because of me issuing the ps command.

The heading caught my attention. I entered ps as a command, and yes the table also says that ps is a command. Now, if all these are commands, would sh -c ps, or if I trim it down to just sh be a valid command?

I tried that and was pleased to see the following output:

BusyBox v1.00 (2011.08.24-03:20+0000) Built-in shell (msh)
Enter 'help' for a list of built-in commands.

#

I was dropped into a shell, and issuing ls now showed all the linux folders like etc, var etc. I could now see all the files, files that had the values for configuring WAN, DHCP, NAS etc.

Conclusion

Seeing the busybox version, it seems the software was never updated after 2011 so it was bound to have more flaws, one of them being what I had just discovered.

Overall it was a good first step in me trying out security testing.

 
Share this