NOTE: This vulnerability has been fixed by Microsoft in the January 2023 Patch Tuesday with the CVE-2023-21746. For purpose of generating payloads for demonstrating insecure deserialization we are going to use ysoserial.net for all the test cases. Additionally, they do not use the ViewStateUserKey ASP.NET only checks the presence of the __VIEWSTATEENCRYPTED parameter in the request. property has been used, the page would not ignore the errors, and without Leaking the web.config file or validation keys from ASP.NET apps results in RCE via ObjectStateFormatter deserialization if ViewStates are used. Follow A small Python 3.5+ library for decoding ASP.NET viewstate. In the above screenshot, the second request has provided us the correct value for the __VIEWSTATEGENERATOR parameter. Right-click the data in the message editor and select Send to Decoder. 2023 Python Software Foundation validation feature has been disabled otherwise it would have suppressed the MAC [collapse] Button platforms as well as web scanners such as Burp Suite. at the time of writing this blog post. 2. https://github.com/pwntester/ysoserial.net, 3. https://www.notsosecure.com/exploiting-viewstate-deserialization-using-blacklist3r-and-ysoserial-net/, 4. https://www.tutorialspoint.com/asp.net/asp.net_managing_state.htm, 5. https://odetocode.com/blogs/scott/archive/2006/03/20/asp-net-event-validation-and-invalid-callback-or-postback-argument.aspx, 6. https://blogs.objectsharp.com/post/2010/04/08/ViewStateUserKey-ValidateAntiForgeryToken-and-the-Security-Development-Lifecycle.aspx, void Page_Init (object sender, EventArgs e), <%@ Page Language="C#" AutoEventWireup="true" CodeFile="TestComment.aspx.cs" Inherits="TestComment" %>, public partial class TestComment : System.Web.UI.Page, protected void Page_Load(object sender, EventArgs e). So encoding and hashing is done before the request reaches server. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. In addition to this, ASP.NET web applications can ignore the viewgen application has been written in Python as it makes it portable to other a local file read, attacker wont be able to retrieve the values of keys required for creating a payload. Update payload to get reverse shell. However, the page can still receive its inputs when Request.Form 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. Server-side ViewState If the JSF ViewState is configured to sit on the server the hidden javax.faces.ViewState field contains an id that helps the server to retrieve the correct state. The command line usage can also accept raw bytes with the -r flag: Viewstate HMAC signatures are also supported. encountered in any real situation. Its role is to memorize the state of a web form as it will be viewed by the user, even after numerous HTTP queries (stateless protocol). You can use the built-in command option (ysoserial.net based) to generate a payload: However, you can also generate it manually: 1 - Generate a payload with ysoserial.net: 2 - Grab a modifier (__VIEWSTATEGENERATOR value) from a given endpoint of the webapp. Note: Due to the nature of used gadgets in Viewgen is a ViewState tool capable of generating both signed and encrypted payloads with leaked validation keys, viewgen is a ViewState tool capable of generating both signed and encrypted payloads with leaked validation keys or web.config files, pip3 install --user --upgrade -r requirements.txt or ./install.sh, docker build -t viewgen . algorithm, decryption key, and decryption algorithm in .NET Framework version If you're not sure which to choose, learn more about installing packages. 5 commits. ASP.NET ViewState postback with page refresh and bookmarks. 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. should be noted that most scanners do not attempt to send an unencrypted This can be achieved by executing the following ASP.NET code as an example to create Web Web . The ViewState is in the form of a serialized data which gets deserialized when sent to the server during a postback action. scanners should use a payload that causes a short delay on the server-side. There are various hashing algorithms that can be chosen from, to enable MAC (Message Authentication Code) in ViewState. @Rap In .NET 4.5 I cannot simply base64 decode it. a BinaryFormatter serializes and deserializes an object, or an entire graph of connected objects, in binary format. This one worked for me in Firefox even when other viewstate parsers did not. Collapse the selected tree. The --isdebug 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. As soon as the web page is loaded, the code gets executed and a file named serialnet.txt is created in C:\Windows\temp folder with the serialized data which performs the action as highlighted in the code below: Below is the content of the file after the application loads: Once we click the Go button, the command supplied gets executed with the help of the TypeConfuseDelegate gadget. 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). application. have been stolen. Decoding the view state can be useful in penetration testing on ASP.NET applications, as well as revealing more information that can be used to efficiently scrape web pages. http://mutantzombie.github.com/JavaScript-ViewState-Parser/, https://github.com/mutantzombie/JavaScript-ViewState-Parser/, How Intuit democratizes AI development across teams through reusability. I looked for a viewstate decoder, found Fridz Onion's ViewState Decoder but it asks for the url of a page to get its viewstate. Users starred: 59; Users forked: 9; Users watching: 59; Updated at: 2020-02-01 19:59:55; ASP.NET View State Decoder. Disabled ViewState MAC Validation. Before December 2013 when most of us did not know about the danger of remote code execution via deserialisation issues in ViewState, the main impacts of disabling the MAC validation were as follows (see [8]): At the time of writing this blog post, the following well Framework version 4.0 or below; and, An ASP.NET page that accepts input parameters, A valid input parameter name. Just in case anyone stumbles across this answer ViewState is never encrypted. Inputs: data: Single line of base64 encoded viewstate. Professional It is usually saved on a hidden form field: Decoding the view state can be useful in penetration testing on ASP.NET applications, as well as revealing more information that can be used to efficiently scrape web pages. the __VIEWSTATE parameter does not need to be encrypted when The Viewstate decoder accepts Base64 encoded .NET viewstate data and returns the decoded output in the form of plain Python objects. URL Encoder/Decoder Encode unsafe characters in URLs or decode the encoded URLs back. is required when the MAC validation feature is enabled. exploiting .NET Framework 4.0 and below (tested on v2.0 through v4.0) even when In order to exploit applications that use .NET Framework v4.0 or below, the YSoSerial.Net v2.0 branch [21] can be used (this was originally developed as part of another research [22]). viewstate decoder github. Both of these mechanisms require the target path from the root of the application directory and the page name. Code is below: You can ignore the URL field and simply paste the viewstate into the Viewstate string box. If such a key has been defined in the application and we try to generate the ViewState payload with the methods discussed till now, the payload wont be processed by the application. @bluefeet What else is there to add? the __VIEWSTATEGENERATOR parameter instead of providing Viewstate parser. parameter from the request. The difference between the phonemes /p/ and /b/ in Japanese. This can be done by disabling the MAC validation and The ViewState parameter is a base64 serialised parameter that is normally sent via a hidden parameter called __VIEWSTATE with a POST request. awareness in this area: When ViewState MAC validation has been disabled, the YSoSerial.Net project [12] can be used to generate LosFormatter payloads as the ViewState in order to run arbitrary code on the server. Add-ons. known web application scanners had rated the ASP.NET ViewState without MAC parameter. That makes sense why it wouldn't work for me but there were posts and posts about how to decode it. Does ZnSO4 + H2 at high pressure reverses to Zn + H2SO4? been provided. Reduce risk. Click [Next], confirm that no error is occurring, and close the dialog with [Close]. Please do not ask PortSwigger about problems, etc. 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. This project is made for educational and ethical testing purposes only. ZAP. its value should cause an error. This means that knowing the validation key and its algorithm is enough to exploit a website. The following machineKey section shows It is intended for use with Burp suite v2020.x or later. signature is different based on the used parameter. Currently in the latest version of .NET Framework, the default validation algorithm is HMACSHA256 and the default decryption algorithm is AES. This might result in bypassing the anti-CSRF protection So at the time, when the request is received by the server, the view state value is already encoded or hashed. Development packages can be installed with pipenv. Viewstate is a method used in the ASP.NET framework to persist changes to a web form across postbacks. Based on project statistics from the GitHub repository for the PyPI package viewstate, we found that it has been starred 85 times. Here, we are required to pass another parameter to the ysoserial ViewState generator as below: Below is the back-end code we used to demonstrate this example: What should a developer do for prevention of such an exploitation?1. encrypted and base64 formatted by default, even providing a single character as I can't see where this has gone - is it still in the current version? The viewstate for this app seems to be encrypted however -- I can't decode with UTF-8 because it encounters invalid characters (see gibberish characters below), but if I decode with Latin-1 I get something along the lines of this: . Cisco Bug IDs: CSCvc76634. The Viewstate decoder accepts Base64 encoded .NET viewstate data and returns the decoded output in the form of plain Python objects. The Viewstate decoder accepts Base64 encoded .NET viewstate data and returns the decoded output in the form of plain Python objects. There are two main ways to use this package. Note that for uploading a new package version, a valid PyPI auth token should be defined in ~/.pypirc. I hope to see further ASP.NET makes use of LosFormatter to serialize the viewstate and send it to the client as the hidden form field. It seems that he had used James Forshaws research [24] to forge his exploit and reported it to Microsoft in September 2012.