Date:         Tue, 5 Dec 2000 10:53:56 -0800
From: "Jeffrey W. Baker" <jwbaker@ACM.ORG>
Subject:      Charles Schwab online trading various lame vulnerabilities
To: BUGTRAQ@SECURITYFOCUS.COM

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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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