[ SOURCE: http://www.secureroot.com/security/advisories/9761225024.html ]

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Security Advisory: Various Charles Schwab online trading problems



*Date



4 December 2000



*Author



Jeffrey W. Baker, email jwbaker@acm.org



*Copyright Statement



This security advisory is Copyright 2000 by Jeffrey William Baker

(jwbaker@acm.org).  The advisory may be distributed in whole or in part

without modification.



*Background



Charles Schwab operates an online securities trading service.  On 25

August 2000 I discovered three security problems with this service.  

Between 25 August and 28 August 2000, I had discussions with Schwab staff,

but with no result.  As of the time of this writing, the flaws still exist

and I have no reason to believe that they are in the process of being

fixed.



*Synopsis



Through cross-site scripting[1], an attacker can gain control of the

account of a Charles Schwab customer who uses the online trading service.  

The attacker can choose to either gain interactive use of the service, or

to cause the account holder to perform inadvertent unwanted actions on the

attacker's behalf.



Additionally, it may be possible to predict a user's login cookie.



*Details



The Schwab trading web site does not properly validate form input.  In

some places, the form input is echoed back to the user's browser without

proper HTML escaping.  Therefore, it is possible for an attacker to cause

JavaScript code to be executed in the user's browser.  The attacker could

use this ability to retrieve the HTTP cookie which Schwab uses for user

authentication.



As a proof-of-concept, a Schwab user could visit this URL, and their login

cookie will be presented to them in a JavaScript alert dialog.  The

proof-of-concept can be easily modified to instead send the login cookie

to an arbitrary HTTP server.  The URL is:



https://investing.schwab.com/trading/trdmoesverify/?menu=2&submenu=1&ADOrderEntryNumber=0&AffirmativeDetermination=0&prenv=N&numOrders=3&Symbol0=foo%22><script>alert(document.cookie)</script><input%20value=%22&TradeType0=Select+One&Quantity0=&OrderType0=&LimitPrice0=&Minimum0=&MinimumQuantity0=&TimeLimit0=Day+Only&StopPrice0=&DoNotReduce0=&AllOrNone0=



There are other locations on the site which exhibit the cross-site

scripting problem.  For example, the forms at

https://investing.schwab.com/trading/quotexec/



Typically, the attacker would need to exploit this problem by causing a

Schwab user to make an HTTP request while logged on to the Schwab service.  

The likely vector for such an attack would be a link or image embedded in

an email or a message on a stock trading bulletin board.  Heavy users of

the service are the most vulnerable.



While I investigated these problems, I noted that the Schwab login cookie

only varied in the first five character positions at each login.  The

first character was always a hex digit, and the other four were in the

range [0-9A-Z].  I did not attempt a cryptanalysis, but I have a moderate

suspicion that it may be possible to predict the login cookie with

reasonable success.



*User Impact



This bug affects potentially all Schwab users.  To defend against this

attack, the user should:



1) disable JavaScript in the browser.  I do not know if the Schwab site

relies on JavaScript for proper operation.



2) not visit any other web sites, read email, or use bulletin boards while

using the Schwab web site.



3) always log off of the Schwab web site when done using it.



4) always close and restart the browser before and after using the Schwab

web site.



*Suggested Resolution



Schwab should examine their programs to ensure proper input validation.  

Their system should use a form key to ensure that form input comes from

the authenticated user interactively.



As an organization, Schwab should strive to fix problems when given

five-month advance notice.  They should raise their ethical standards to

alert their paying customers whenever a system vulnerability is reported.



*Footnotes



[1] CERTŪ Advisory CA-2000-02 Malicious HTML Tags Embedded in Client Web

Requests.  http://www.cert.org/advisories/CA-2000-02.html

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