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diff --git a/users/tazjin/blog/posts/reversing-watchguard-vpn.md b/users/tazjin/blog/posts/reversing-watchguard-vpn.md new file mode 100644 index 0000000000..f1b779d8d9 --- /dev/null +++ b/users/tazjin/blog/posts/reversing-watchguard-vpn.md @@ -0,0 +1,158 @@ +TIP: WatchGuard has +[responded](https://www.reddit.com/r/netsec/comments/5tg0f9/reverseengineering_watchguard_mobile_vpn/dds6knx/) +to this post on Reddit. If you haven\'t read the post yet I\'d recommend +doing that first before reading the response to have the proper context. + +------------------------------------------------------------------------ + +One of my current client makes use of +[WatchGuard](http://www.watchguard.com/help/docs/fireware/11/en-US/Content/en-US/mvpn/ssl/mvpn_ssl_client-install_c.html) +Mobile VPN software to provide access to the internal network. + +Currently WatchGuard only provides clients for OS X and Windows, neither +of which I am very fond of. In addition an OpenVPN configuration file is +provided, but it quickly turned out that this was only a piece of the +puzzle. + +The problem is that this VPN setup is secured using 2-factor +authentication (good!), but it does not use OpenVPN\'s default +[challenge/response](https://openvpn.net/index.php/open-source/documentation/miscellaneous/79-management-interface.html) +functionality to negotiate the credentials. + +Connecting with the OpenVPN config that the website supplied caused the +VPN server to send me a token to my phone, but I simply couldn\'t figure +out how to supply it back to the server. In a normal challenge/response +setting the token would be supplied as the password on the second +authentication round, but the VPN server kept rejecting that. + +Other possibilities were various combinations of username&password +(I\'ve seen a lot of those around) so I tried a whole bunch, for example +`$password:$token` or even a `sha1(password, token)` - to no avail. + +At this point it was time to crank out +[Hopper](https://www.hopperapp.com/) and see what\'s actually going on +in the official OS X client - which uses OpenVPN under the hood! + +Diving into the client +---------------------- + +The first surprise came up right after opening the executable: It had +debug symbols in it - and was written in Objective-C! + + + +A good first step when looking at an application binary is going through +the strings that are included in it, and the WatchGuard client had a lot +to offer. Among the most interesting were a bunch of URIs that looked +important: + + + +I started with the first one + + %@?action=sslvpn_download&filename=%@&fw_password=%@&fw_username=%@ + +and just curled it on the VPN host, replacing the username and +password fields with bogus data and the filename field with +`client.wgssl` - another string in the executable that looked like a +filename. + +To my surprise this endpoint immediately responded with a GZIPed file +containing the OpenVPN config, CA certificate, and the client +*certificate and key*, which I previously thought was only accessible +after logging in to the web UI - oh well. + +The next endpoint I tried ended up being a bit more interesting still: + + /?action=sslvpn_logon&fw_username=%@&fw_password=%@&style=fw_logon_progress.xsl&fw_logon_type=logon&fw_domain=Firebox-DB + +Inserting the correct username and password into the query parameters +actually triggered the process that sent a token to my phone. The +response was a simple XML blob: + +```xml +<?xml version="1.0" encoding="UTF-8"?> +<resp> + <action>sslvpn_logon</action> + <logon_status>4</logon_status> + <auth-domain-list> + <auth-domain> + <name>RADIUS</name> + </auth-domain> + </auth-domain-list> + <logon_id>441</logon_id> + <chaStr>Enter Your 6 Digit Passcode </chaStr> +</resp> +``` + +Somewhat unsurprisingly that `chaStr` field is actually the challenge +string displayed in the client when logging in. + +This was obviously going in the right direction so I proceeded to the +procedures making use of this string. The first step was a relatively +uninteresting function called `-[VPNController sslvpnLogon]` which +formatted the URL, opened it and checked whether the `logon_status` was +`4` before proceeding with the `logon_id` and `chaStr` contained in the +response. + +*(Code snippets from here on are Hopper\'s pseudo-Objective-C)* + + + +It proceeded to the function `-[VPNController processTokenPrompt]` which +showed the dialog window into which the user enters the token, sent it +off to the next URL and checked the `logon_status` again: + +(`r12` is the reference to the `VPNController` instance, i.e. `self`). + + + +If the `logon_status` was `1` (apparently \"success\" here) it proceeded +to do something quite interesting: + + + +The user\'s password was overwritten with the (verified) OTP token - +before OpenVPN had even been started! + +Reading a bit more of the code in the subsequent +`-[VPNController doLogin]` method revealed that it shelled out to +`openvpn` and enabled the management socket, which makes it possible to +remotely control an `openvpn` process by sending it commands over TCP. + +It then simply sent the username and the OTP token as the credentials +after configuring OpenVPN with the correct config file: + + + +... and the OpenVPN connection then succeeds. + +TL;DR +----- + +Rather than using OpenVPN\'s built-in challenge/response mechanism, the +WatchGuard client validates user credentials *outside* of the VPN +connection protocol and then passes on the OTP token, which seems to be +temporarily in a \'blessed\' state after verification, as the user\'s +password. + +I didn\'t check to see how much verification of this token is performed +(does it check the source IP against the IP that performed the challenge +validation?), but this certainly seems like a bit of a security issue - +considering that an attacker on the same network would, if they time the +attack right, only need your username and 6-digit OTP token to +authenticate. + +Don\'t roll your own security, folks! + +Bonus +----- + +The whole reason why I set out to do this is so I could connect to this +VPN from Linux, so this blog post wouldn\'t be complete without a +solution for that. + +To make this process really easy I\'ve written a [little +tool](https://github.com/tazjin/watchblob) that performs the steps +mentioned above from the CLI and lets users know when they can +authenticate using their OTP token. |