This cheatsheet will introduce the basics of SSTI, along with some evasion techniques we gathered along the way from talks, blog posts, hackerone reports and direct experience.
It would result in 49 in Twig, in Jinja2, and neither if no template language is in use. This step is sometimes as trivial as submitting invalid syntax, as template engines may identify themselves in the resulting error messages.
Note that there are other methods to identify more template engines. Tplmap or its Burp Suite Plugin will do the trick. This guide will specifically focus on Jinja2. Read the docs for more.
Basically, you can crawl up the inheritance tree of the known objects using mrothus accessing every class loaded in the current python environment! The usual exploitation starts with the following: from a simple empty string "" you will create a new-type object, type str.
If you happen to have the source code of the application, look for the flask. There are several sources from which objects end up in the template context. Remember that there may be sensitive viper4android uninstall zip xda explicitly added by the developer, making the SSTI easier. You can use this list by albinowax to fuzz common variable names with Burp or Zap.
The following global variables are available within Jinja2 templates by default:. If you want to explore in major details their globals, here are the links to the API docs: Flask and Jinja.
You may conduct introspection with the locals object using dir and help to see everything that is available to the template context. You can also use introspection to reach every other application variable. This script written by the DoubleSigma team will traverse over child attributes of request recursively. For example, if you need to reach the blacklisted config var you may access it anyway via:. The request. Injecting '' should be enough to shut down the server.
Information Security Stack Exchange is a question and answer site for information security professionals. It only takes a minute to sign up. RCE is usually obtained by uploading the reverse shell script on the target, thanks to a file reference, accesses by using the object.
Unfortunately, in the output I get, there isn't any file referenceso I'm not able to upload the reverse shell.
After further research, I think I figured out why.
Exploring SSTI in Flask/Jinja2, Part II
It seems that the latest versions of Python are not vulnerable to the metodology briefly explained in my original post. The Flask web app I was using as target was indeed running inside a Docker container, with the latest version of Python installed. Sign up to join this community.
The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Asked 11 months ago. Active 2 months ago.
Cheatsheet - Flask & Jinja2 SSTI
Viewed times. Response page Oops! That page doesn't exist. What am I missing? Active Oldest Votes. A simple way to check it out: Python 2. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Featured on Meta. Community and Moderator guidelines for escalating issues via new response….
Feedback on Q2 Community Roadmap. Related Hot Network Questions. Question feed.Grab nunjucks. Read more about the differences of these files in Getting Started. By moving our templates to the client, transfer sizes are reduced and page responsiveness increases significantly. Our API supplies data, meaning we can decouple testing the front-end from testing the back-end. Nunjucks has made our app feel native. Webmaker from the Mozilla Foundation encourages people to create. Using web technologies, you can create visually rich media with a powerful real-time tool.
Using nunjucks, it was easy to collaborate on the templates and implement complex features such as localization. There haven't been any problems with performance or stability.
We chose Nunjucks because of its close relationship with the Jinja and Twig languages, and also for its test coverage and robust implementation.
Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I have a variable in my code that is buried deep in some legacy code. Rather than spend all day searching for it, I'd like to just print out the variable from within the jinja template.
Is that possible? However, it sounds like the variable wasn't passed to the template. Check for that. If you're doing a lot of debugging, try Flask-DebugToolbarit'll print out all the variables that got passed to your template so you don't have to muck around with print statements like this.
Useful stuff. This will call Python during template generation, will get the value for your variable, and return it to the template.
Learn more. Asked 5 years, 9 months ago. Active 5 years, 7 months ago. Viewed 11k times. Brandon Brandon 1, 5 5 gold badges 15 15 silver badges 19 19 bronze badges. You can write a custom filter, jinja. Active Oldest Votes. Rachel Sanders Rachel Sanders 4, 17 17 silver badges 31 31 bronze badges.
You need context-processors. Example to put on your. Lovato Lovato 1, 11 11 silver badges 19 19 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook.
Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Featured on Meta. Community and Moderator guidelines for escalating issues via new response…. Feedback on Q2 Community Roadmap. Technical site integration observational experiment live on Stack Overflow. Dark Mode Beta - help us root out low-contrast and un-converted bits.
This could easily be achieved by setting up an intercepting proxy and study the requests and responses made by the application to the web sever. Also, trying to trigger error messages on the application can also give away a lot of information about the application under test.
In the screenshot below in the response of the we find the python version that is running, accompanied with the server "Werkzeug". This is a clear indicator the web application might be running python flask, and python flask typically runs with the templating engine, jinja2. Now that we have determined the type of application that is running let's try to see if any user supplied input is accepted by the application. So now we have control of whatever is being reflected on the page.
How do we now determine if the application might be susceptible to Server Side Template Injection? First we need to do some investigation on how the syntax works, so we dive into the docs!
And here we find the following information. Now, we want to use expressions to print to the template output to see if our payloads are interpreted and executed on the server-side by the templating engine. The most ideal way to do so is to inject mathematical statements. As found in the docs:. Let's see what happens of we inject the expression with the operator described above! Read the docs for more.
Basically, you can crawl up the inheritance tree of the known objects using mrothus accessing every class loaded in the current python environment. Now, lets find some usefull injections for Jinja2. In order to build our exploit this here already looks pretty promising:. After injecting the payload we now have a list of all the different classes loaded in our target application.
Let's see if we can use it to read some information from the file system.
Subscribe to RSS
On position 40 whilst iterating over the different loaded classes we find the "read" function. As mentioned before this attack can ultimately be used also to gain remote code execution on the target application. In order to do so we first would need to set up a listener and than inject the following payloads. KBID 3 - Cross site scripting attribute. KBID 3 - Cross site scripting href. KBID 13 - File upload. KBID 20 - Clickjacking. KBID 29 - Brute force login. KBID 44 - Authorisation missing.
KBID 45 - Exposed docker daemon. KBID - parameter binding attack. KBID - Tabnabbing. KBID - Insecure direct object references. Powered by GitBook.My initial goal was to find a path to file or operating system access. I was previously unable to do so, but thanks to some feedback on the initial article, I have since been able to achieve my goal. This article is the result of the additional research. In response to the initial article, Nicolas G published the following tweet.
I have no desire to act like I know more about this stuff than I do. By starting with a new-type object, e. Yes, this gives us access to every class loaded in the current python environment. So, how do we leverage this new found capability? We are after a universal exploit, so we want to set up our test environment to be as close to native Flask as possible. The more we add to the application in the way of imported libraries and 3rd party modules, the less universal our attack vector will become.
In the previous article, we had to add some functionality to the vulnerability in order to conduct introspection. This is no longer required.
The first thing we want to do is is select a new-style object to use for accessing the object base class. We can simply use ''a blank string, object type str. We can see the previously discussed tuple being returned to us. As you can see, there is a lot of stuff here. In the target app I am using, there are accessible classes. The goal is to find something useful that leads to file or operating system access.
It is probably not all that uncommon to find classes like subprocess. Luckily, there is capability in native Flask that allows us to achieve similar behavior. This is the key to file system access. While open is the builtin function for creating file objects, the file class is also capable of instantiating file objects, and if we can instantiate a file object, then we can use methods like read to extract the contents.
The previous article referenced several methods of the config object that load objects into the Flask configuration environment. The most obvious is the use of the compile function against the contents of a file whose path is provided as a parameter. This would come in handy if we had a way to write files to the operating system, no? Well, as we just discussed, we do! We can use the aforementioned file class to not only read files, but write them to world writeable locations on the target server.
This is a 2 staged attack. The code will execute upon compilation. Remote Code Execution achieved. While running code is great and all, having to go through a multi-step process for each block of code we want to run is tedious. Notice the difference between the following before and after images.Please consider reading both parts in their entirety. Part 2 can be found here. As security professionals, we are in the business of helping organizations make risk-based decisions.
Seeing as risk is a product of impact and likelihood, without knowing the true impact of a vulnerability, we are unable to properly calculate the risk. This article is the result of that research. The scenario behind this code is that the developer thought it would be silly to have a separate template file for a small page, so he created a template string within the view function.
Pretty reasonable, right? Most people who see this behavior immediately think XSS, and they would be right.Jinja2 Templating Engine Tutorial
This is a good example of that. Now that we have a working exploit, the next step is to dig into the template context and find out what is available to an attacker of the application through the SSTI vulnerability. Modify the vulnerable view function of the proof-of-concept application to look as follows.
There are several sources from which objects end up in the template context. Item 3 is application dependent and can be accomplished in a number of ways. This stackoverflow discussion contains a few examples.
We make our first interesting discovery by introspecting the request object. Within the request object is an object named environ. The request.
You guessed it. An extremely low effort denial-of-service. This method does not exist when running the applicatiom using gunicorn, so the vulnerability may be limited to the development server. Our second interesting discovery comes from introspecting the config object.
- Important questions for class 11 geography in hindi
- In campeggio con i bambini
- Android checkselfpermission
- Forces unit study guide answer key pdf
- Atom note