[NEWS] Mozilla Cookie StealingFrom: firstname.lastname@example.org
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From: firstname.lastname@example.org To: email@example.com Date: Thu, 24 Jan 2002 13:34:48 +0100 (CET)
The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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Mozilla Cookie Stealing
Cookies are often used to identify and authenticate users to a website. If
an attacker can steal a user's cookies, then they can impersonate that
user. The completeness of the impersonation and the actions the attacker
can perform as that user depend on how the particular site uses the
A bug in Mozilla allows an attacker to steal the user's cookies for any
given domain if the attacker can convince the user's browser to load a
given URL. It does not require that active scripting is enabled in the
browser, and can be done with something as simple as an image tag,
allowing for hassle free use in HTML email, web based email services, etc.
Netscape versions prior to 6.2.1
Mozilla versions prior to 0.9.7
Netscape version 6.2.1
Mozilla version 0.9.7
Cookies are the mechanism used by most websites to identify and
authenticate a user. If you can steal someone's cookies, you can trick the
server into thinking you are that other server. Exactly what this gains
you depends on the application and how it is designed. It may gain you
very little, or it may gain you a whole lot (e.g.
<http://alive.znep.com/~marcs/passport/> Microsoft Passport to Trouble).
For more information about cookies, see
<http://www.cookiecentral.com/faq/> The Unofficial Cookie FAQ.
Cookies are set with a specific hostname or a domain, so that they are
only sent to that host or domain, with an exception or two. They can also
be set with a specific path, or with the secure flag, which means they
will only be sent if the connection is a SSL connection. Normally, this
should mean that only the server that set the cookie, or others it is
operating in cooperation with (e.g. in the same domain) can read it.
Mozilla has a bug that lets you bypass this protection and steal cookies
for any domain. This is quite similar to bugs found in Microsoft Internet
Explorer in the past (see
http://alive.znep.com/~marcs/security/iecookie2/). As has been shown
repeatedly, there are many security flaws in many Microsoft products.
Sadly, they are far from being alone. There is almost certainly no web
browser out there that is functional enough to browse a significant
percent of current popular websites and that does not have similar
Loading a URL such as:
Will cause Mozilla to connect to the hostname specified before the "%00",
but send the cookies to the server based on the entire hostname. The "%00"
is the URL encoded version of the null character, used in C to terminate
This exploit can be used to steal cookies with a specific path set, and
can be used to steal cookies with the secure flag set, by using the
specific path and SSL in the request URL. Note, however, that cookies set
for a specific hostname (e.g. "www.passport.com") cannot be stolen using
this method, but only cookies set for an entire domain (e.g.
An example exploit is available. It is in fact very straightforward:
The information has been provided by <mailto:firstname.lastname@example.org> Marc Slemko.
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