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Vulnerability Note VU#707100Multiple web-based email services fail to filter malicious characters when the message contains cascading style sheet character escapingOverviewAn attacker can send a specially crafted email message to a victim containing malicious scripting (JavaScript, VBScript, JScript, etc.), active content, or potentially HTML. When a victim views the message with scripting enabled, the victim's browser will then interpret this javascript which can lead to several impacts.I. DescriptionMalicious code provided by one client for another clientSites that provide email service with web interfaces have guarded against a vulnerability where one client embeds malicious HTML tags in a message intended for another client with in the body of a message. For example, an attacker might send an email message like
To: victim@example.com Subject: Hello Hello Victim, This is a message. <SCRIPT>malicious code</SCRIPT> This is the end of my message. When a victim with scripts enabled in their browser reads this message, the malicious code may be executed unexpectedly. Scripting tags that can be embedded in this way include <SCRIPT>, <OBJECT>, <APPLET>, and <EMBED>. With client-to-client sites, developers explicitly recognize that data input is untrustworthy when it is presented to other users. Most email services either will not accept such input or will encode/filter it before sending anything to other readers. It has recently been discovered that some sites that provide email services with web interfaces are failing to check for tags that have been encoded in the message body. The following message would be an example of this:
To: victim@example.com Subject: Hello Hello Victim, This is a message. <\73CRIP\T>malicious code<\/\73CRIP\T> This is the end of my message. Note that the email message does not need to originate from the same domain. This vulnerability is closely related to Cross-Site Scripting. For more information on Cross-Site Scripting, see http://www.cert.org/advisories/CA-2000-02.html. Yahoo!, Excite, and Outblaze (Mail.com) are all services that have been reported vulnerable to this attack. Hotmail and Lycos Mail are reported to be not vulnerable. II. ImpactMalicious scripting, HTML and Active Content can be executed in the victim's browser. This attack could be used to gain sensitive data such as passwords, credit card numbers, address book entries and any arbitrary information the user inputs. This may also lead to the theft of credentials.III. SolutionPlease review the Systems Affected section to determine if your vendor is vulnerable, and whether they have taken any action to remedy this vulnerability.Do not open messages that you feel may contain untrustworthy content. Even if the message originates from a known person. Also, you can set your browser's security settings to disable scripting and active content. This will limit, but not mitigate the attack vectors for this vulnerability, but will also decrease the functionality of your service.
Referenceshttp://www.kb.cert.org/vuls/id/361600 Thanks to Finjan Software for reporting this vulnerability. This document was written by Jason A Rafail.
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