29 May 2001 This is the third of 3 sequential advisories we are issuing regarding Aladdin eSafe Gateway. Status -------- The entire content of this advisory was reviewed and acknowledged by Aladdin. Product Background -------------------------- eSafe Gateway is an Internet Content Security product. You can configure eSafe Gateway to remove scripts (VBScripts, JavaScripts) and other executable tags from incoming HTML documents. Alternatively, the administrator can ban certain scripting commands from appearing inside scripts. The banned commands will be removed, while the rest of the HTML page is left intact. Scope -------- eDvice recently conducted a test of eSafe's ability to remove scripts from HTML documents. Although scripts are widely used by many web-sites, some organizations requesting to allow only limited use of Internet access from their internal network, prefer to disable scripting capabilities in order to avoid various known, as well as yet to be found, browser-based attacks. The Findings ---------------- eSafe does not recognize scripting tags constructed using extended Unicode notation. This allows an attacker to bypass eSafe script filtering mechanism and introduce malicious code into an organization. Details --------- eSafe gateway analyzes the incoming HTML file and searches for the keyword "<SCRIPT'. From the moment the keyword was found, eSafe looks for a following "</Script>" keyword and then replaces the entire content between these keywords with spaces. However, browsers such as Internet Explorer accept extended Unicode character representation within HTML files. If the string "<SCRIPT" is replaced with some extended Unicode representation, then eSafe will not filter the tag and the browser will run the script. Exploit ---------- See Attached file (unzip it first). To repeat this vulnerability, place the file on your web server and configure eSafe to remove all scripts. Access the file using the browser and you will see the message "hello" on your screen. This is a message generated by a VBScript script that should have been filtered. Solution ----------- Do not rely on eSafe Gateway version 3.0 for HTML filtering until Aladdin fixes the problem. Aladdin will publish a workaround to avoid this vulnerability and will address this issue in the next release of eSafe Gateway. ==================== Discovered by: eDvice Security Services supportat_private http://www.edvicetech.com Tel: +972-3-6120133 Fax: +972-3-6954837 begin 666 script38a.zip M4$L#!!0````(`$=QO2JS]/CJP@```/\````.````<V-R:7!T,SAA+FAT;6P] MC\$*@D 0AN]![S#LW>P40:Y@M660"K4%'3?;<F%S3<>HY^AU(NS-4JQ.'_SS MS\>,X_-@Z78[CL^\:<. <0]"+V"4S%G(5AZ/5@0F)D69(B6!BG-3F"/"5A6E MT+#&\J ,#'I]\E^/?VV4-[03/.L1Q(G("XETPV?6D$""F%GR4JHK_;HM?L]D MH^ +OF2N8[>L`_MWVSB:[FI6S_<CSE6&H$5Z*L5)TNO^&U4OH66.0'RIM2'5 MT_X/&M/8'.ZMLGW[`U!+`0(4`!0````(`$=QO2JS]/CJP@```/\````.```` M``````$`( "V@0````!S8W)I<'0S.&$N:'1M;%!+!08``````0`!`#P```#N %```````` ` end
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