Skip to main content

XML Injection

Description:

XML Injection is an attack technique used to manipulate or compromise the logic of an XML application or service. The injection of unintended XML content and/or structures into an XML message can alter the intend logic of the application. Further, XML injection can cause the insertion of malicious content into the resulting message/document.


How to Exploit:

Inserting hacker@evil.com</Email><UniqueID>0</UniqueID><Email>hacker@evil.com in Email field will yield the following result:

<UserRecord>
<UniqueID>123</UniqueID>
<Name>Henry Ackerman</Name><Email>
hacker@evil.com</Email><UniqueID>0</UniqueID><Email>hacker@evil.com&lt;/Email>
<Address>123 Disk Drive</Address>
<ZipCode>98103</ZipCode>
<PhoneNumber>206-123-4567</PhoneNumber>
</UserRecord>

This will add more one record in XML database with UniqueID=0.



One Live Example:

In order of doing a Web Application Server Assessment we came across something which was vulnerable to XML Injection. We found that the input field was not properly validating the input given by the user. That means there was no XML validation on part of contents and length of the input supplied by the user. The application didn’t have XML Schema (xsd file) against which the XML was being validated.

The application had one admin module where User management function was implemented. The admin can add user, delete user, manage its profile and assign roles and privileges to them.


We entered valid user information in all the respective filed in order to add a user:



We captured the request in proxy. All the data in respective fields were going into XML format as you can see in the here:


We inserted a valid XML payload confirming to the all the required fields required to add a valid user and that adheres to the valid XML structure. You can see the highlighted payload which is being inserted into ‘CustomerView’ filed of the XML:



Upon forwarding the result the application successfully accepts the request and instead of creating a user in the name of ‘validuser’ the application creates another user in the name of ‘hackman’:



Thus an attacker acting as Man in the Middle attack will successfully create a user of his choice and login into the application in unauthorized way.


Countermeasures:


Do not trust client input.

Validate input: length, range, format, and type.

Validate XML streams.

Constrain, reject, and sanitize input.

Encode output.

Restrict the size, length, and depth of parsed XML messages.






Comments

Popular posts from this blog

Ardilla- New tool for finding SQL Injection and XSS

Three Researchers -- MIT's Adam Kiezun , Stanford's Philip Guo , and Syracuse University's Karthick Jayaraman -- has developed a new tool ' Ardilla ' that automatically finds and exploits SQL injection and cross-site scripting vulnerabilities in Web applications. It creates inputs that pinpoint bugs in Web applications and then generates SQL injection and XSS attacks. But for now Ardilla is for PHP -based Web app only. The researchers say Ardilla found 68 never-before found vulnerabilities in five different PHP applications using the tool -- 23 SQL injection and 45 XSS flaws. More information is awaited. For their attack generation techniques refer to their document at: http://www.cs.washington.edu/homes/mernst/pubs/create-attacks-tr054.pdf

Combining power of Fiddler with Burp

Both are pretty powerful tools when it comes to intercept and modify http communications. But at some point of time, they become even more powerful combo if tied with each other. They complement each other. In a recent pentest I came across a similar situation where in Burp was not able to intercept a specific kind of traffic and Fiddler came to rescue. The application was designed to upload video. The initial communication was straight forward, I mean logging into application, filling up the video details etc. And all these were easily captured by Burp except the point where you hit the Upload Video and it connects to a different server and surprisingly it was not captured by Burp, not sure why, even after repeated attempts. So, I fired Fiddler to see if the it sees this request. But it's a;ways to play with requests using Burp due to it's various functionalities like, Intruder, Repeaters etc. But it was necessary to capture this request in Burp. So the below steps can be

File Upload through Null Byte Injection

Sometimes, during file upload we come across situation wherein there would be check on the file extension at the client side as well as server side too. If the application does allow only .jpeg extension to be uploaded, the client side java script checks for the extension of the file before passing the request. We all know that how easily this can be defeated. Some applications, checks for the extension at the server side also. That's not easy to bypass. However there are some ways with which it still can be bypassed. Most of server side scripts are written in high level languages such as Php, Java etc who still use some C/C++ libraries to read the file name and contents. That leads to the problem. In C/C++ a line ends with /00 or which is called Null Byte. So whenever the interpreter sees a null byte at the end of the a string, it stops reading thinking it has reached at the end of the string. This can be used for the bypass. It works for many servers, specially php servers. T