SEC-CONSULT Security Advisory 20051021-0 =================================================================================== title: Yahoo/MSIE XSS program: Yahoo Webmail in combination with MSIE 6.0 (maybe other browsers) homepage: www.yahoo.com found: 2005-04 by: SEC-Team / SEC-CONSULT / www.sec-consult.com =================================================================================== Vulnerabilty overview: --------------- Since april 2005 SEC-Consult has found 5+ serious vulnerabilities within Yahoo's webmail systems. All of them have been fixed in the production environment. Nevertheless SEC-Consult believes that input-validation thru blacklists can just be a temporary solution to problems like this. From our point of view there are many other applications vulnerable to this special type of problem where vulnerabilities of clients and servers can be combined. Vulnerabilty details: --------------- 1) XSS / Cookie-Theft Yahoos blacklists fail to detect script-tags in combination with special characters like NULL-Bytes and other META-Characters. This leaves Webmail users using MSIE vulnerable to typical XSS / Relogin-trojan / Phishing attacks. 2) Some XSS Examples from our advisories Excerpt from HTML-mails: ================================================================================================ SCRIPT-TAG: ---cut here---

hello

alert("i have you now")
rrrrrrxxxxx
---cut here--- ================================================================================================ OBJECT-TAG: ---cut here--- ---cut here--- ================================================================================================ ONERROR-Attribute: ---cut here--- uargg

---cut here--- ================================================================================================ ONUNLOAD-Attribute: ---cut here---

somewords

---cut here--- ================================================================================================ Recommended hotfixes for webmail-users --------------- Do not use MS Internet-Explorer. Recommended fixes --------------- Do not use blacklists on tags and attributes. Whitelist special/meta-characters. Vendor status: --------------- Vulnerabilities have been fixed. General remarks --------------- We would like to apologize in advance for potential nonconformities and/or known issues. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SEC-Team / www.sec-consult.com / _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.grok.org.uk/full-disclosure-charter.html Hosted and sponsored by Secunia - http://secunia.com/