D-Link DIR-100D1 Authentification-bypass

(post recovered after backup-issues, thanks to Archive.org)
After the previous set of bugs was discovered (read my previous blog-post about it here), D-Link implemented access controls. This made most commands and variables protected. So for example, an unauthentificated can’t ask for the administrative password in B13 and B15 nor can he do other naughty stuff an ill-behaved unauthentificated user may want to do (I’m considering writing more on that in a later blog-post) but he can ask for the current system language, that’s not too dangerous, now is it?

An inquisitive mind, will note that multiple cliget-commands can be batched together in one HTTP-request. If the unauthentificated user asks for say /cliget.cgi?cmd=$sys_user1%;$poe_user%;$poe_pass, the router will tell him rightfully of, those are all protected variables and this is the expected result. However, let’s say the first variable isn’t a protected variable, let’s say the request is for /cliget.cgi?cmd=$sys_language%;$sys_user1%;$poe_user%;$poe_pass. As you’ll notice, this just asks for the current language in addition to all the previously mentioned hush-hush-stuff, the correct response would be for the router to tell him off again but unless it runs on a firmware I’m about to link you to, it’ll say “he asked for the language, the admin-credentials and the poe-credentials, language seems good go right ahead then” and let the unauthentificated user read the administrative password, amongst other things.


This should be seen as a good lesson for the importance of correct array usage; if you take an array, validate all elements before taking them for granted, don’t just check the first and be done with it.


This issue has been fixed in 4.03 B13_fam2 (ftp://dlinktemp:dlinktemp2015@ Yes, I know downloading from IPs, especially IPs not registred in a block owned by the device manufacturer seems shady, I don’t like it but that’s the link I got so that’s what I can give you, the firmwares don’t seem to be neither signed nor encrypted nor do any public hashes/hashfiles from a reputable source exist so you choose if you trust me or not, though the official D-Link twitter-account has apparently refered to it before (https://twitter.com/dlink/status/181876200338231297).


For the record, I don’t hate the DIR-100D1, I’ve grown rather fond of mucking about with it and if there’s interest, I’ll write more about what I’ve done to the poor thing and learned from mucking about.

Hacking the DIR-100 rev. D1

So, let’s say you have this router, the DIR-100 revision D1, I did. Being bored, I went the login screen but since the password was not the default I was unable login. So I cranked open Chromes fantastic development tools.


Now, I sent random values to try to capture some traffic and lo and behold there was a several requests made to /cliget.cgi?cmd=$… . The client-side code was loading configuration-data using XHR, including a partial MD5 of the password! Trying more values I discovered that if I requested /cliget.cgi?cmd=$, I would get the entire configuration file, including the username and password! The router was giving away admin access to everyone with access to the login page (LAN, or if remote admin is enabled LAN+WAN).


Later, revisiting the router I discovered that the thing didn’t check the HTTP Origin header, meaning that a basic CSRF attack could successfully perform a login, given a known username and password. I also discovered the /cli.cgi?cmd= API that is used by the client-side code to change the configuration setting, which also proved unable to hinder basic CSRF attacks. Using a simple link and i bit of JavaScript a hacker could take control of someones network including but not limited to redirecting traffic.


After watching a bit of WarGames (the 80’s flick that thaught us that every system has a help function) I got this funky idea, that would happen if I requested help from the router? Apparently, a lot, you get a list of every command in the system, including amongst other dhcps (lists all DHCP-clients), mem, reboot and GDB (supposedly not GNU GDB).  One of the first thing i tried executing, was gdb which crashed the system, it might be that it triggers a debugger  Connected to the internal 3-pin serial port. mem however is quite a different beast, it’s a memory monitor like debug.com of DOS-past. That’s right: you can read and write memory on the device without authentification.


In addition to all this, I have it from credible sources that the router is plagued by the wide-spread UPnP portmap-from-wan bug that was detected, which means that an attacker may use the router for connection-bouncing and/or presumably use the UPnP bug to gain access to the internal admin-panel.

I will however remark that there has been some mention of the cliget.cgi and cli.cgi APIs before http://forum.nag.ru/forum/index.php?showtopic=58050&st=20.

So, as any responsible man would do, I attempted to contact D-Link, to no avail. D-Link has also made it difficult to track down firmware upgrades for the router.

I ask that anyone handling this information does so with care, and that D-Link makes sufficient arrangements for their unprotected customers.