ViewState payload can also be encrypted to avoid WAFs when the decryptionKey Although not knowing the value of this parameter can stop our attack, its value can often be found in the cookies or in a hidden input parameter ([17] shows an implemented example). Developer's common vision of a ViewState is a large hidden HTML field (see. Parse the viewstate data by decoding and unpacking it. URLENCODED data is okay ''' # URL Encoding: urldelim = "%" # Check to see if the viewstate data has urlencoded characters in it and remove: if re. View state is part of the ASP Web Forms framework. Base64 Encoder/Decoder Encode the plain text to Base64 or decode Base64 to the plain text. For purpose of demo we have used a sample application with below code base and with an assumption that web.config file has been accessed by the attacker due to any file read vulnerabilities: Now upon hosting this application in IIS we tried to intercept the functionality of the application using burp suite as shown below: Now, we can see that ViewState MAC has been enabled. A tag already exists with the provided branch name. Some examples for .NET are: PSObject, TextFormattingRunProperties and TypeConfuseDelegate. When the GO button is clicked in the application, this data is read back from the file and then deserialized with the help of ObjectStateFormatter. In order to make ViewState tamper free there are options to even make ViewState MAC enabled due to which an integrity check would be performed on the ViewState value during deserialization by setting the value. Is there a tool or a website exist that can help viewing the contents of viewstate? ASP.NET page as an example to make this clearer: The following screenshot shows the Home; Blog; Videos . After all, ASP.net needs to decrypt it, and that is certainly not a black box. the defined Purpose strings handle the serialization format used by .NET version 1 because that @ahwm True story. Add development tools in Pipfile and update README, https://github.com/mutantzombie/JavaScript-ViewState-Parser, http://viewstatedecoder.azurewebsites.net/, https://referencesource.microsoft.com/#System.Web/UI/ObjectStateFormatter.cs,45, https://msdn.microsoft.com/en-us/library/ms972976.aspx. algorithm, decryption key, and decryption algorithm in .NET Framework version Add-ons. removing the __VIEWSTATE parameter from the request or by adding the __PREVIOUSPAGE the __VIEWSTATE Community. However, as the ViewState do not use the MAC [Decode] Button Get help and advice from our experts on all things Burp. Just in case anyone stumbles across this answer ViewState is never encrypted. This can be done by disabling the MAC validation and As the __PREVIOUSPAGE parameter is path tree in IIS: You can check [20] if you are not familiar with virtual directory and application terms in IIS. I need to see the contents of the viewstate of an asp.net page. version is sorely outdated and therefore too unlikely to be This was identified by reviewing the .NET Framework source code [6]. whilst performing a major part of this research. Any official documents would be gladly accepted to help improve the parsing logic. ASP.NET web applications use ViewState in order to maintain a page state and persist data in a web form. A novel encoder-decoder network-based model is proposed for trend prediction in this work. The ViewState is in the form of a serialized data which gets deserialized when sent to the server during a postback action. First, it can be used as an imported library with the following typical use case: Failed to load latest commit information. Its purpose is to persist the state of server controls . The following blog posts are related to this research: A video link for Immunity Canvas was added to the references and also in the Other tools section. Before I go into details, first need to know what is view state. Install $ pip install viewstate Usage. After replacing the URL encoded value of the generated payload with the value of the __VIEWSTATE in the above shown request, our payload will execute. Low. parameter has been encrypted. A tag already exists with the provided branch name. Euler: A baby on his lap, a cat on his back thats how he wrote his immortal works (origin?). Connect and share knowledge within a single location that is structured and easy to search. First, it can be used as an imported library with the following typical use case: It is also possible to feed the raw bytes directly: Alternatively, the library can be used via command line by directly executing the module: Which will pretty-print the decoded data structure. As the targeted box might not send any requests externally, automated @Rap In .NET 4.5 I cannot simply base64 decode it. First, it can be used as an imported library with the following typical use case: decode ('utf8') else: d1 = copy . developments in these tools to support the missing features. For better understanding, we will understand various test cases and look at each one of them practically. This might be Please do not ask PortSwigger about problems, etc. scanners should use a payload that causes a short delay on the server-side. This attack allows for arbitrary file read/write and elevation of privilege. have been stolen. The purpose of "ViewState" is to memorize the state of the user, even after numerous HTTP queries (stateless protocol). is required to check whether the MAC validation is disabled when the __VIEWSTATE rather than txtMyInput.Text. I would like to thank Subodh Pandey for contributing to this blog post and the study without which I could not have had an in-depth insight on this topic.. Before getting started with ViewState deserialization, let's go through some key terms associated with ViewState and its exploitation. The ViewState is basically generated by the server and is sent back to the client in the form of a hidden form field _VIEWSTATE for POST action requests. choice for an attacker. Can you trust ViewState to handle program control? This post has been nominated in the pwnie for most under-hyped research category in 2019 pwnie awards [30]! It is automatically maintained across posts by the ASP.NET framework.When a page is sent back to the client, the changes in the properties of the page and its controls are determined, and stored in the value of a hidden input field named _VIEWSTATE. Development packages can be installed with pipenv. The Viewstate decoder accepts Base64 encoded .NET viewstate data and returns the decoded output in the form of plain Python objects. caused by using this tool. #decode_viewstate(encoded_viewstate, algo: 'sha1') Object. Viewstate is a method used in the ASP.NET framework to persist changes to a web form across postbacks. As mentioned previously, parts when the MaxPageStateFieldLength property has been set to a positive value. Disabled ViewState MAC Validation. Catch critical bugs; ship more secure software, more quickly. viewstate-decoder.py. an example: It should be noted that when a machineKey section has not been defined within the configuration files or when the validationKey and decryptionKey attributes have been set to AutoGenerate, the application generates the required values dynamically based on a cryptographically random secret. property to False does not stop this attack 3. I answered a similar question recently, Getting values from viewstate using JQuery?. The Collapse the selected tree. useful to bypass some WAFs when ViewState chunking is allowed. However, we can see below that the payload got executed and a file test.txt with content 123 was created successfully. a 10-second delay: The above code could be executed using the ActivitySurrogateSelector gadget of YSoSerial.Net. rev2023.3.3.43278. I've been . In the case . ASP.NET makes use of LosFormatter to serialize the viewstate and send it to the client as the hidden form field. . base64 string in the __VIEWSTATE parameter. There are two main ways to use this package. The data is in the top panel. Microsoft .NET ViewState Parser and Burp suite extension ViewStateDecoder, https://github.com/raise-isayan/BurpExtensionCommons, https://github.com/google/gson/blob/master/LICENSE. x-up-devcap-post-charset Header in ASP.NET to Bypass WAFs Again! I hope to see further Now click the button. If we notice the POST request above, we can see that there isnt a _VIEWSTATEGENERATOR parameter in the request. When the page is again posted back, the _VIEWSTATE field is sent to the server with the HTTP request. Based on project statistics from the GitHub repository for the PyPI package viewstate, we found that it has been starred 85 times. Now, we can create a serialized payload using ysoserial.net as shown below: The command used above to generate the payload is: Using the above generated payload in the ViewState parameter and using it in the HTTP POST request, we can observe the payload getting executed as below: CASE 2: When ViewState is removed from the HTTP request: In this case study we will cover the scenario where developers try to remove ViewState from becoming part of an HTTP Request. the actual ASP.NET error messages. Unit tests and code formatting tasks can be run with the builtin scripts: For PyPI releases, follow the build, check and upload scripts. 2ASP.NET . parameter that might be in use to stop CSRF attacks. ready made graham cracker crust recipes / ac valhalla ciara romance consequences / viewstate decoder github. The Viewstate decoder accepts Base64 encoded .NET viewstate data and returns the decoded output in the form of plain Python objects. Its default value is negative the __VIEWSTATE parameter does not need to be encrypted when Ensure that custom error pages are in use and users cannot see Downloads: 2 This Week. signature is different based on the used parameter. pip install viewstate Note that for uploading a new package version, a valid PyPI auth token should be defined in ~/.pypirc. You are correct. README.md. Decode the view state ; Return True if the message is valid ; Parses the given buffer and returns the result ; Parse b ; Parse a . Users starred: 59; Users forked: 9; Users watching: 59; Updated at: 2020-02-01 19:59:55; ASP.NET View State Decoder. GitHub page. 3 - Generate the signed/encrypted payload: 4 - Send a POST request with the generated ViewState to the same endpoint. It seems Immunity Canvas supports creating the ViewState parameter when the validation and encryption keys are known [29]. The following list shows how to mitigate risks of this Overall impact: See [13] for more details. GitHub - martabyte/viewstate-decoder: Quick python script to decode ASP.NET ViewState. HTTP Debugger App. Prior to the .NET Framework version 4.5, the __VIEWSTATE Minimising the environmental effects of my dyson brain. Regenerate any disclosed / previously compromised validation / decryption keys. Therefore, it is If you're not sure which to choose, learn more about installing packages. ASP.NET View State Decoder. I managed to use the TextFormattingRunProperties gadget in YSoSerial.Net to exploit Since there is no publically available specification of how .NET viewstate is encoded, reverse engineering was based on prior work: https://github.com/mutantzombie/JavaScript-ViewState-Parser, http://viewstatedecoder.azurewebsites.net/, https://referencesource.microsoft.com/#System.Web/UI/ObjectStateFormatter.cs,45, https://msdn.microsoft.com/en-us/library/ms972976.aspx. The Viewstate decoder accepts Base64 encoded .NET viewstate data and returns the decoded output in the form of plain Python objects. Browser Headers Viewer, Knowledge Base Is it correct to use "the" before "materials used in making buildings are"? This worked on an input on which the Ignatu decoder failed with "The serialized data is invalid" (although it leaves the BinaryFormatter-serialized data undecoded, showing only its length). $ viewgen -h usage: viewgen [-h] [--webconfig WEBCONFIG] [-m MODIFIER] [--viewstateuserkey VIEWSTATEUSERKEY] [-c COMMAND] [--decode] [--guess] [--check] [--vkey VKEY] [--valg VALG] [--dkey DKEY] [--dalg DALG] [-u] [-e] [-f FILE] [--version] [payload] viewgen is a ViewState tool capable of generating both signed and encrypted payloads with leaked validation keys or web.config files positional . The following shows an example: Another option for a stand-alone website would be to set the This means that in the latest .NET Framework versions the decryption key and Asking for help, clarification, or responding to other answers. What is the purpose of this D-shaped ring at the base of the tongue on my hiking boots? Basic Java Deserialization (ObjectInputStream, readObject) CommonsCollection1 Payload - Java Transformers to Rutime exec () and Thread Sleep. Fixed some issues with ViewState in the existing Burp suite. Home Blog Videos Documentation Community Download. Lets create our payload using ysoserial.net and provide the validation key and algorithm as parameters along with app path and path. No gadget was identified to exploit .NET Framework v1.1 at In order to generate a ViewState for the above URL, the Additionally, they do not use the ViewStateUserKey The world's #1 web penetration testing toolkit. has been disabled or by knowing the: In order to prevent manipulation attacks, .NET Framework can sign and encrypt the ViewState that has been serialised using the LosFormatter class [1]. an exploit has been executed successfully on the server-side. Bulk update symbol size units from mm to map units in rule-based symbology. the __VIEWSTATEGENERATOR parameter instead of providing is not a new attack. Specify the ViewState to be decoded in . When the __PREVIOUSPAGE parameter This parser was a huge help during testing as it facilitated easy decoding and identifying viewstate issues on web applications. For ASP.NET framework 4.5, we need to supply the decryption algorithm and the decryption key to the ysoserial payload generator as follows: The path and apppath parameters above can be decided with the help of a little debugging. validation feature has been disabled otherwise it would have suppressed the MAC The Viewstate decoder accepts Base64 encoded .NET viewstate data and returns the decoded output in the form of plain Python objects. valid ViewState can be forged. In the past, I've used this website to decode it: http://www.motobit.com/util/base64-decoder-encoder.asp. An example. Framework version 4.0 or below; and, An ASP.NET page that accepts input parameters, A valid input parameter name. In brief, ViewState is a Base64 encoded string and is not readable by the human eye. Viewstate variable lost on user control loaded dynamically, ASP.NET Viewstate Optimization/Analyzing Tools, Odd Behavior with Viewstate on Dynamically Loaded Control. There was an interesting presentation from Alexandre Herzog in November 2014 regarding exploiting the deserialisation issues in SharePoint when the MAC validation was disabled in certain pages [23]. is required. It is possible to If a POST request is used, the __VIEWSTATE We can force the usage of ASP.NET framework by specifying the below parameter inside the web.config file as shown below. You signed in with another tab or window. Follow For the sake of an example, we will be using the below code. If we add ViewState parameter to the request body and send our serialized payload created using ysoserial, we will still be able to achieve code execution as shown in CASE 1. One may assume that if ViewState is not present, their implementation is secure from any potential vulnerabilities arising with ViewState deserialization. the paths: It uses the ActivitySurrogateSelector gadget by default Staging Ground Beta 1 Recap, and Reviewers needed for Beta 2, Determine how much data is being stored in ViewState per control. The vulnerability occurs because a "tomcat" user on the system can run certain shell commands, allowing the user to overwrite any file on the filesystem and elevate privileges to root. If you find a bug in CyberChef, please raise an issue in our GitHub repository explaining it in as much detail as possible. It Code. Quoting from my previous answer: If you are writing the control for your own consumption and you only need to read from ViewState, you could do so, but I wouldn't . The best manual tools to start web security testing. or docker pull 0xacb/viewgen. I can't see where this has gone - is it still in the current version? Now, lets see the execution of the code at runtime. gadget can be changed to: Knowledge of used validation and seeing the actual error message, it is hard to say whether the MAC validation Note that it is also possible to decode using the command line. validation error message. The command line usage can also accept raw bytes with the -r flag: Viewstate HMAC signatures are also supported. https://github.com/mutantzombie/JavaScript-ViewState-Parser, http://viewstatedecoder.azurewebsites.net/, https://referencesource.microsoft.com/#System.Web/UI/ObjectStateFormatter.cs,45, https://msdn.microsoft.com/en-us/library/ms972976.aspx. until finding a ViewState that can execute code on the server (perhaps by ASP.NET decides The decryptionKey and its algorithm are not required This has been the first way that actually works for me. Get started with Burp Suite Professional. The ObjectStateFormatter class [2] performs the signing, encryption, and verification tasks. Now right click on the page > View Source. argument. Basically, by default ViewState is just Base64-encoded, so you can decode it as long as the administrator hasn't configured the site to encrypt it. I would like to thank Subodh Pandey for contributing to this blog post and the study without which I could not have had an in-depth insight on this topic. Cisco Bug IDs: CSCvc76634. The following URL shows an Since there is no publically available specification of how .NET viewstate is encoded, reverse engineering was based on prior work: Any official documents would be gladly accepted to help improve the parsing logic. Debug JAVA Applications. No key is needed. parameter is known, it can be used for the ASP.NET applications that use .NET Cannot retrieve contributors at this time. Contact Us, Latest Changes length that limits the type of gadgets that can be used here. As you can set the machine keys (for validation and decryption) to a known value in web.config you could then use this to decrypt manually if necessary. Expand the selected tree. Here is the source code for a ViewState visualizer from Scott Mitchell's article on ViewState (25 pages), And here's a simple page to read the viewstate from a textbox and graph it using the above code. CASE 1: Target framework 4.0 (ViewState Mac is disabled): It is also possible to disable the ViewState MAC completely by setting the AspNetEnforceViewStateMac registry key to zero in: Now, once this is done we will go for the exploitation phase. You need to include a reference to "System.Web" in your project if you paste this into a console application. A small Python 3.5+ library for decoding ASP.NET viewstate. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. viewstate decoder github. property has been used, the page would not ignore the errors, and without The command line usage can also accept raw bytes with the -r flag: Viewstate HMAC signatures are also supported. parameter in the request (it does not need to have any value). of course, you are correct. How can I entirely eliminate all usage of __VIEWSTATE on a single page? Online Viewstate Viewer made by Lachlan Keown: http://lachlankeown.blogspot.com/2008/05/online-viewstate-viewer-decoder.html. The response will be output in JSON format. As another person just mentioned, it's a base64 encoded string. is required when the MAC validation feature is enabled. e.g. be all in lowercase or uppercase automatically. . This means that knowing the validation key and its algorithm is enough to exploit a website. As mentioned previously, it is important to find the root of First, it can be used as an imported library with the following typical use case: +1 Good Link to the Online View State Decoder simple to use and worked. __gv + ClientID + __hidden, Validation key and its This can be achieved by executing the following ASP.NET code as an example to create Legal / Privacy / Eula Select the operation you want to perform on the data from the controls beside the data panel. attack: Exploiting untrusted data deserialisation via the ViewState parameter in the URL via a GET request. Donate today! Exploiting a deserialisation issue via __EVENTVALIDATION is more restricted and requires: Value Contribute to scottj/viewstate-decoder development by creating an account on GitHub. all systems operational. We discussed an interesting case of pre-published Machine keys, leading [1] https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.losformatter, [2] https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.objectstateformatter, [3] https://devblogs.microsoft.com/aspnet/farewell-enableviewstatemac/, [4] https://www.owasp.org/index.php/Anti_CSRF_Tokens_ASP.NET, [5] https://docs.microsoft.com/en-us/previous-versions/aspnet/hh975440(v=vs.120), [6] https://github.com/Microsoft/referencesource/blob/master/System.Web/Util/AppSettings.cs#L59, [7] https://github.com/Microsoft/referencesource/blob/master/System.Web/UI/Page.cs#L4034, [8] https://www.troyhunt.com/understanding-and-testing-for-view/, [9] https://portswigger.net/kb/issues/00400600_asp-net-viewstate-without-mac-enabled, [10] https://www.netsparker.com/web-vulnerability-scanner/vulnerabilities/viewstate-mac-disabled/, [11] https://www.acunetix.com/vulnerabilities/web/view-state-mac-disabled/, [12] https://github.com/pwntester/ysoserial.net/, [13] https://docs.microsoft.com/en-us/dotnet/api/system.web.configuration.machinekeysection, [14] https://docs.microsoft.com/en-us/dotnet/api/system.web.configuration.machinekeysection.compatibilitymode, [15] https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.control.templatesourcedirectory, [16] https://docs.microsoft.com/en-us/previous-versions/dotnet/articles/ms972969(v=msdn.10), [17] https://software-security.sans.org/developer-how-to/developer-guide-csrf, [18] https://github.com/pwntester/ysoserial.net/tree/master/ysoserial/Plugins/ViewStatePlugin.cs, [19] https://github.com/pwntester/ysoserial.net/tree/v2/ysoserial/Plugins/ViewStatePlugin.cs, [20] https://docs.microsoft.com/en-us/iis/get-started/planning-your-iis-architecture/understanding-sites-applications-and-virtual-directories-on-iis, [21] https://github.com/nccgroup/VulnerableDotNetHTTPRemoting/tree/master/ysoserial.net-v2, [22] https://www.nccgroup.trust/uk/about-us/newsroom-and-events/blogs/2019/march/finding-and-exploiting-.net-remoting-over-http-using-deserialisation/, [23] https://www.slideshare.net/ASF-WS/asfws-2014-slides-why-net-needs-macs-and-other-serialization-talesv20, [24] https://media.blackhat.com/bh-us-12/Briefings/Forshaw/BH_US_12_Forshaw_Are_You_My_Type_Slides.pdf, [25] https://docs.microsoft.com/en-us/security-updates/SecurityAdvisories/2013/2905247, [26] https://www.blackhat.com/docs/us-17/thursday/us-17-Munoz-Friday-The-13th-JSON-Attacks-wp.pdf, [27] https://www.slideshare.net/MSbluehat/dangerous-contents-securing-net-deserialization, [28] https://speakerdeck.com/pwntester/dot-net-serialization-detecting-and-defending-vulnerable-endpoints?slide=54, [29] https://vimeopro.com/user18478112/canvas/video/260982761, [30] https://web.archive.org/web/20190803165724/https://pwnies.com/nominations/, Danger of Stealing Auto Generated .NET Machine Keys, IIS Application vs. Folder Detection During Blackbox Testing, https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.losformatter, https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.objectstateformatter, https://devblogs.microsoft.com/aspnet/farewell-enableviewstatemac/, https://www.owasp.org/index.php/Anti_CSRF_Tokens_ASP.NET, https://docs.microsoft.com/en-us/previous-versions/aspnet/hh975440(v=vs.120), https://github.com/Microsoft/referencesource/blob/master/System.Web/Util/AppSettings.cs#L59, https://github.com/Microsoft/referencesource/blob/master/System.Web/UI/Page.cs#L4034, https://www.troyhunt.com/understanding-and-testing-for-view/, https://portswigger.net/kb/issues/00400600_asp-net-viewstate-without-mac-enabled, https://www.netsparker.com/web-vulnerability-scanner/vulnerabilities/viewstate-mac-disabled/, https://www.acunetix.com/vulnerabilities/web/view-state-mac-disabled/, https://github.com/pwntester/ysoserial.net/, https://docs.microsoft.com/en-us/dotnet/api/system.web.configuration.machinekeysection, https://docs.microsoft.com/en-us/dotnet/api/system.web.configuration.machinekeysection.compatibilitymode, https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.control.templatesourcedirectory, https://docs.microsoft.com/en-us/previous-versions/dotnet/articles/ms972969(v=msdn.10), https://software-security.sans.org/developer-how-to/developer-guide-csrf, https://github.com/pwntester/ysoserial.net/tree/master/ysoserial/Plugins/ViewStatePlugin.cs, https://github.com/pwntester/ysoserial.net/tree/v2/ysoserial/Plugins/ViewStatePlugin.cs, https://docs.microsoft.com/en-us/iis/get-started/planning-your-iis-architecture/understanding-sites-applications-and-virtual-directories-on-iis, https://github.com/nccgroup/VulnerableDotNetHTTPRemoting/tree/master/ysoserial.net-v2, https://www.nccgroup.trust/uk/about-us/newsroom-and-events/blogs/2019/march/finding-and-exploiting-.net-remoting-over-http-using-deserialisation/, https://www.slideshare.net/ASF-WS/asfws-2014-slides-why-net-needs-macs-and-other-serialization-talesv20, https://media.blackhat.com/bh-us-12/Briefings/Forshaw/BH_US_12_Forshaw_Are_You_My_Type_Slides.pdf, https://docs.microsoft.com/en-us/security-updates/SecurityAdvisories/2013/2905247, https://www.blackhat.com/docs/us-17/thursday/us-17-Munoz-Friday-The-13th-JSON-Attacks-wp.pdf, https://www.slideshare.net/MSbluehat/dangerous-contents-securing-net-deserialization, https://speakerdeck.com/pwntester/dot-net-serialization-detecting-and-defending-vulnerable-endpoints?slide=54, https://vimeopro.com/user18478112/canvas/video/260982761, https://web.archive.org/web/20190803165724/https://pwnies.com/nominations/.
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