Evading Cisco AnyConnect blocking LAN connections

Author: dnet

Some VPNs allow split tunneling, however, Cisco AnyConnect and many other solutions offer a way for network administrators to forbid this. When that happens, connecting to the VPN seals off the client from the rest of the LAN. As it turns out, breaking this seal is not that hard, which can be useful for special cases like performing pentests over a VPN designed for average users.

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Decrypting Eazfuscator.NET encrypted symbol names

Author: dnet

There are many obfuscators for different languages, and some of those offer reversible options for easier field debugging. Eazfuscator.NET is one of these and with a bit of reverse engineering, whole files can be restored with the original symbols once you have the password.

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Our take on social engineering

Author: dnet

Like many other offensive IT security companies, we also offer social engineering assessments. And like in other areas of our portfolio, we try to steer client needs in a way that they order something that actually matters. This blog post summarizes what we experienced and how we see things in this field. While many things work the same way around the globe, the starting point is our feeling here in Hungary, where many people in the local IT security scene think social engineering means walking into buildings dressed as a pizza delivery guy and calling targets on the phone.

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The curious case of encrypted URL parameters

Author: dnet

As intra-app URLs used in web applications are generated and parsed by the same code base, there’s no external force pushing developers towards using a human-readable form of serialization. Sure, it’s easier to do debugging and development, but that’s why I used the word “external”. Many frameworks use custom encodings, but one of the most extreme things a developer can do in this regard is completely encrypting request parameters. We encountered such a setup during a recent web app security assessment, let’s see how it worked out.

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Snow cannon vs. unique snowflakes — testing registration forms

Author: dnet

Many of the web application tests we conducted had a registration form in the scope. In such cases, there’s usually a field that needs to be unique for each invocation, sometimes called username, in other cases, the e-mail address is used as such. However, launching the Scanner or Intruder of Burp Suite or a similar tool will send the same username over and over again, resulting in possible false negatives. We faced this problem long enough that we came up with a solution for it, and now you can use it too!

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Not so unique snowflakes

Author: dnet

When faced with the problem of identifying entities, most people reach for incremental IDs. Since this requires a central actor to avoid duplicates and can be easily guessed, many solutions depend on UUIDs or GUIDs (universally / globally unique identifiers). However, although being unique solves the first problem, it doesn’t necessarily cover the second. We’ll present our new solution for detecting such issues in web projects in the form of an extension for Burp Suite Pro below.

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Beyond detection: exploiting blind SQL injections with Burp Collaborator

Author: dnet

It’s been a steady trend that most of our pentest projects revolve around web applications and/or involve database backends. The former part is usually made much easier by Burp Suite, which has a built-in scanner capable of identifying (among others) injections regarding latter. However, detection is only half of the work needed to be done; a good pentester will use a SQL injection or similar database-related security hole to widen the coverage of the test (obviously within the project scope). Burp continually improves its scanning engine but provides no means to this further exploitation of these vulnerabilities, so in addition to manual testing, most pentesters use standalone tools. With the new features available since Burp Suite 1.7.09, we’ve found a way to combine the unique talents of Burp with our database exploitation framework, resulting in pretty interesting functionality.

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Accessing local variables in ProGuarded Android apps

Author: dnet

Debugging applications without access to the source code always has its problems, especially with debuggers that were built with developers in mind, who obviously don’t have this restriction. In one of our Android app security projects, we had to attach a debugger to the app to step through heavily obfuscated code.

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Detecting ImageTragick with Burp Suite Pro

Author: dnet

After ImageTragick (CVE-2016–3714) was published, we immediately started thinking about detecting it with Burp, which we usually use for web application testing. Although collaborator would be a perfect fit, as image processing can happen out-of-band, there’s no official way to tap into that functionality from an extension.

The next best thing is timing, where we try to detect remote code execution by injecting the sleep command which delays execution for a specified amount of seconds. By measuring the time it takes to serve a response without and the with the injected content, the difference tells us whether the code actually got executed by the server.

We used rce1.jpg from the ImageTragick PoC collection and modified it to fit our needs. By calling System.nanoTime() before and after the requests and subtracting the values, the time it took for the server to respond could be measured precisely.

Since we already had a Burp extension for image-related issues, this was modified to include an active scan option that detects ImageTragick. The JPEG/PNG/GIF detection part was reused so that it could detect if any parameters contain images, and if so, it replaces each (one at a time) with the modified rce1.jpg payload. The code was released as v0.3 and can be downloaded either in source format (under MIT license) or a compiled JAR for easier usage. Below is an example of a successful detection:

issue screenshot

Header image © Tomas Castelazo, www.tomascastelazo.com / Wikimedia Commons / CC-BY-SA-3.0


iOS HTTP cache analysis for abusing APIs and forensics

Author: dnet

We’ve tested a number of iOS apps in the last few years, and got to the conclusion that most developers follow the recommendation to use APIs already in the system – instead of reinventing the wheel or unnecessarily depending on third party libraries. This affects HTTP backend APIs as well, and quite a few apps use the built-in NSURLRequest class to handle HTTP requests.

However, this results in a disk cache being created, with a similar structure to the one Safari uses. And if the server doesn’t set the appropriate Cache-Control headers this can result in sensitive information being stored in a plaintext database.

Like others in the field of smartphone app security testing, we’ve also discovered such databases within the sandbox and included it in the report as an issue. However, it can also be helpful for further analysis involving the API and for forensic purposes. Still, there were no ready to use tools, which is problematic in such a convoluted format.

The cache can usually be found in Library/Caches/[id]/Cache.db where [id] is application-specific, and is a standard SQLite 3 database, as it can be seen below.

$ sqlite3 Cache.db
SQLite version 3.12.1 2016-04-08 15:09:49
Enter ".help" for usage hints.
sqlite> .tables
cfurl_cache_blob_data       cfurl_cache_response
cfurl_cache_receiver_data   cfurl_cache_schema_version

Within these tables, all the information can be found that can be used to reconstruct the requests issued by the app along with the responses. (Well, almost; in practice, the lack of HTTP version and status text is not a big problem.)

Since we use Burp Suite for HTTP-related projects (web applications and SOAP/REST APIs), an obvious solution was to develop a Burp plugin that could read such a database and present the requests and responses within Burp for analysis and using it in other modules such as Repeater, Intruder or Scanner.

As the database is an SQLite one, the quest began with choosing a JDBC driver that supports it; SQLiteJDBC seemed to be a good choice, however it uses precompiled binaries for some platforms, which limits its compatibility. After the first few tests it also became apparent that quite a few parts of JDBC is not implemented, including the handling of BLOBs (raw byte arrays, optimal choice for storing complex structures not designed for direct human consumption). The quick workaround was to use HEX(foo) which results in a hexadecimal string of the blob foo, and then parsing it in the client.

BLOBs were used for almost all purposes; request and response bodies were stored verbatim (although without HTTP Content Encoding applied, see later), while request and response metadata like headers and the HTTP verb used were serialized into binary property lists, a format common on Apple systems. For the latter, we needed to find a parser, which was made harder by the fact that most solutions (be it code or forum responses) expected the XML-based representation (which is trivial to handle in any language) while in this case the more compact binary form was used. Although there are utilities to convert between these two (plutil, plistutil and others), I didn’t want to add an external command line dependencies and spawn several processes for every request.

Fortunately, I found a project called Quaqua that had a class for parsing the binary format. Although it also tried converting the object tree to the XML format, a bit of modification fixed this as well.

With these in place, I could easily convert the metadata to HTTP headers, and append the appropriate bodies (if present). For UI, I got inspiration from Logger++ but used a much simpler list for enumerating the requests, since I wanted a working prototype first. (Pull requests regarding this are welcome!)

Most of the work was solving small quirks, for example as I mentioned, HTTP Content Encoding (such as gzip) was stripped before saving the body, however the headers referred to the encoded payload, so both the Content-Length and the Content-Encoding headers needed to be removed, and former had to be filled based on the decoded (“unencoded”) body.

Below is a screenshot of the plugin in action, some values had been masked to protect the innocent.

screenshot of the plugin

The source code is available on GitHub under MIT license, with pre-built JAR binaries downloadable from the releases page.

Featured image is Apfelteiler by Frank C. Müller licensed under CC BY-SA