In the “A Novel Way of Abusing IPv6 Extension Headers to Evade IPv6 Security Devices” blogpost I described a way to evade a high-end commercial IDPS device, the Tipping Point IDPS (TOS Tipping Point, Package 3.6.1.4036 and vaccine 3.2.0.8530 digital), by abusing a minor detail at the IPv6 specification. As I promised at the end of that blogpost, this is not the end. In this blogpost I am going to describe several new and different ways of evading another popular IDPS, an open-source one this time, Suricata.
Recently we started playing around with Cisco’s virtual router, the CSR 1000V, while doing some protocol analysis. We found Cisco offering an BIN file for download (alternatively there is an ISO file which contains a GRUB boot loader and the BIN file, or an OVA file which contains a virtual machine description and the ISO file) and file(1) identifies it as DOS executable:
$ file csr1000v-universalk9.03.12.00.S.154-2.S-std.SPA.bin
csr1000v-universalk9.03.12.00.S.154-2.S-std.SPA.bin: DOS executable (COM)
We didn’t manage to get the file running, neither in a (Free-)DOS environment, nor in a wine virtual DOS environment, except using the boot loader from the ISO file. So we became curious as for the structure and ingredients of the file.
As we continue our research in the 3GPP protocol world, there is a new tool for you to play with. It is called s1ap_enum and thats also what it does 😉
The tool itself is written in erlang, as i found no other free ASN.1 parser that is able to parse those fancy 3GPP protocol specs. It connects to an MME on sctp/36412 and tries to initiate a S1AP session by sending an S1SetupRequest PDU. To establish a S1AP session with an MME the right MCC and MNC are needed in the PLMNIdentity. The tool tries to guess the right MCC/MNC combinations. It comes with a preset of known MCC/MNC pairs from mcc-mnc.com, but can try all other combinations as well.
As it is well known to the IPv6 enthusiasts, one of the most significant changes that IPv6 brings with it, apart from supporting a really huge address space, is the improved support for Extensions and Options, which is achieved by the usage of IPv6 Extension headers. According to RFC 2460, “changes in the way IP header options are encoded allows for more efficient forwarding, less stringent limits on the length of options, and greater flexibility for introducing new options in the future.” So, by adding IPv6 Extension headers, according to the designers of the protocol, flexibility and efficiency in the IP layer is improved.
This can definitely be the case, but apart from it, it has already been shown that by abusing IPv6 Extension headers several security issues may arise (see for example my presentations at Black Hat Abu Dhabi 2012 and at the IPv6 Security Summit @ Troopers 13). This is why Enno Rey by talking straight to the point at the latest IPv6 Security Summit @ Troopers 14 described the IPv6 Extension headers as a “mess”!
In the course of a recent penetration test, we came across an Image validation vulnerability in Django when using the Python-Imaging-Library (PIL) which we want to explain in this post.
Everybody who doesn’t know what Django and/or the PIL is:
Django is a framework to create web applications with Python (comparable to Rails or Zend). The PIL is a powerful standard python library which provides a toolset to modify, display and verify images of many different formats.
Applications that support the upload of images and validate the file type of those images using the PIL contain an interesting attack vector. For this attack vector, the most interesting image formats are X Bitmap (xbm) and the similar X PixMap (xpm). These two types are text based image files, which contain code to create a monochrome (xbm) or 256 color (xpm) image. In a web server system, these files can be abused to put content (eg. Python/PHP/Code or HTML files) on the server, as long as they pass the image validation process.
This results in the following possible exploitation scenario:
Every system with a Django-Server and PHP-enabled webserver sharing the same document root folder is a possible target for the described, as long as the storage paths for uploaded content are known, accessible and the content and extension of the uploaded files remain untouched (e.g.: no conversion takes place). Those paths can often be guessed as there are several default options.
Uploading python code is also an option, but may only be exploitable in case it is possible to upload to the main folder of the django application (to add malicious functionality). This scenario also requires wide knowledge about the used application, since it is required to find a way to make the application call the code in the uploaded source-files. In addition to this, Django has a very strict policy that forces the administrator to manually add any application to the Django-Server configuration. Even if the upload of a new django app succeeds, it will not be executed by the server, because it is not added to the configuration file yet. For this example, we thus resorted to the scenario with a PHP-enabled server.
To illustrate this scenario, I’m using the django-avatar app on an Xubuntu machine. First of all, a minimal configuration of django-avatar and apache was set up, running in the same document root folder, enabling us to upload avatars for a specific user using the avatar application.
Notice the following default values of django-avatar that enable us to actually exploit this scenario:
Hashing for filenames and userdirnames is disabled by default which makes it easy to determine the path where uploaded content is stored. But even if these options are enabled, it is still possible to access the file- and username directory by just using the corresponding MD5 hashes (no salt is applied).
The most important setting is ALLOWED_FILE_EXTS, which allows every PIL validated image to be uploaded when set to None. Setting this parameter to comma separated strings will lead to exclusively accepting the given extensions [e.g. (“jpg”, “gif”,) leads to only accepting “.jpg” and “.gif ”-files].
To start the exploitation and upload an actual image, we have to login and then browse to the /avatar/add sub-URL, showing the following website:
It is a simple upload page which allows setting avatars. The avatar is not being displayed, since it is not set yet.
We are now uploading a simple xbm file (script.php) with the following content:
Lines starting with a # are comments in xbm definitions. The part after line 3 is the Javascript to empty the page and the PHP-payload, which we use to execute arbitrary PHP code on the server. The actual image is not defined, but PIL will still recognize this file as a valid image, since it contains all the relevant syntax for a valid xbm image and ends with a ;. What comes after line 3 is just ignored by the PIL parser, since it is irrelevant to the image. So the PIL will verify the image and will allow the app to save the image in the avatar directory, where an additional resized version of the image is being generated and saved. The original file will be stored in the directory without any changes to filename, extension and content (except for a hashed filename, if enabled).
After uploading the file, a new avatar is created for the user which appears on disk and in the django admin panel:
Given the apache server is running in the same directory, we now have our own php file on the server and can access all php functions. In our PoC we see the cleaned website with the additional PHP-Version information:
This process can be further exploited, since django-avatar will not overwrite files (instead create a renamed version of the same file: test.jpg and test_1.jpg) and stores old avatars when operating in default settings. Instead of uploading a harmless script to display the server version it is possible to upload a full php webshell and then further exploit the underlying webserver.
The django developers explicitly warn (see “Where should this code live?”) administrators to not run a classic server system (e.g. Apache) in the same directory as the django-server, meaning the overall chance of exploitation is low. Additionally exploitation is only possible if files are stored with their original extension, since the PHP-server will interpret the files depending on their file extension.
Even though this is not a vulnerability in the Django framework (it actually is a kind of a specific scenario), we still need to put more attention to this possible design pitfall, when using powerful libraries like the PIL. We further recommend the following best practices when developing Django applications or any upload-enabled web applications:
• Restrict (image-)file formats
• Do not store the original file on the disk, but instead convert every file to a specific format and only store the converted files.
• Delete unused data
• Set default values as safe as possible (people are lazy and tend to leave things that run untouched)
With this said: Happy coding and until next time! 🙂
On Saturday, April 26 Microsoft announced that Internet Explorer version 6 until version 11 is under potential risk against drive-by attacks from malicious websites, regardless of the underlying Microsoft operating system and the associated memory protection features integrated with the operating system. Microsoft has assigned CVE-2014-1776 to this unknown use-after-free vulnerability, which in the worst case could allow remote code execution if a user views a specially crafted website. If an attacker successfully exploits this vulnerability, s/he will gain the same rights and privileges as the current user (once again, activated User Account Control [UAC] helps keeping privileges of the user low).
The recommended mitigating controls from Microsoft, especially unregistering the VGX.DLL library has led to the misunderstanding, that many people thought the vulnerability is located in the VGX.DLL library. That is wrong. Instead, the vulnerability is located in mshtml.dll, mshtml.tlb, Microsoft-windows-ie-htmlrendering.ptxml, and Wow64_microsoft-windows-ie-htmlrendering.ptxml and therefore unregistering of the above library does not globally mitigate the vulnerability. It only mitigates a specific attack vector where Vector Markup Language (VML) is being used during the attack. Continue reading “The Role of VGX.DLL in the Context of the Latest IE 0-Day”
a few weeks ago I held a talk at UnFUCK, a small University con from students for students. I had decided to give a short talk on “Owning Stuff via USB” aka how to use our TR14 Badge! During the preparations and while building my demos, I tested my new USB RubberDucky. One rather “trivial” demo was actually to use it as a keyboard on an Android phone.
The below post was originally written on February 9th as a little educational exercise & follow-up to my BinDiff post. (This research was actually triggered by a relative asking about that strange Fritz!Box vulnerability he heard about on the radio). Once we realized the full potential of the bug we decided against publishing the post and contacted several parties instead. Amongst others this contributed to the German BSI press release. Given the cat is out of the bag now anyway, we see no reason to hold it back. We will further take this as an opportunity to lay out our basic vulnerability disclosure principles in a future post. This topic will also be discussed in the panel “Ethics of Security Work & Research” at Troopers
Fritz!Box is series of DSL and WLAN routers produced by AVM. They are extremely popular in Germany and are the uncontested market leader for private DSL customers. Recently, a significant number of Fritz!Box owners became victim of an attack that resulted in calls to expensive international numbers. The newspaper “Der Westen” reported about a case where phone calls valued over 4200€ were initiated from a compromised Fritz!Box. Few days later AVM published a security update for a large number of Fritz!Box models and urged customers to apply the patch as soon as possible.
However, no further details about the vulnerability were published. This blog post describes our analysis of the vulnerability that we performed directly after the first updates were released.
I recently got in contact with Intel AMT for the first time. Surely I had heard about it, knew it was “dangerous”, it was kind of exploitable and had to be deactivated. But I hadn’t actually seen it myself. Well, now I have, and I simply love it and you will probably, too (and don’t forget: love and hate are very very close to each other 😉 )
The following blogpost will be a set of features and instructions on how to own a device with an unconfigured copy of Intel AMT without using any complicated hacks or the famous magic! Continue reading “How to use Intel AMT and have some fun with Mainboards”
This is a guest post from Antonios Atlasis
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Hi,
my name is Antonios and I am an independent IT Security Researcher from Greece. One of my latest “hobbies” is IPv6 and its potential insecurities so, please let me talk to you about my latest experience on this.
This week, I had the opportunity to work together with the ERNW guys at their premises. They had built an IPv6 lab that included several commercial IPv6 security devices (firewalls, IDS/IPS and some high-end switches) and they kindly offered their lab to me to play with (thank you guys 🙂 – I always liked …expensive toys). The goal of this co-operation was two-fold: First, to test my new (not yet released) IPv6 pen-testing tool and secondly, to try to find out any IPv6-related security or operational issues on these devices (after all, they all claim that they are “IPv6-Ready”, right?).
