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Two Vulnerabilities in Mozilla may lead to remote compromise

From: Mind Warper (mindwarperlinuxmail.org)
Date: Tue Jul 13 2004 - 05:16:32 CDT

Two Vulnerabilities in Mozilla may lead to remote compromise.

Vendor Information:

Homepage : http://www.mozilla.org
Vendor : informed on 11/06/04
Mailed advisory: 13/06/04
Vender Response : None yet

Affected Versions:

All version of Mozilla and Firefox


There are two vulnerabilities in Mozilla that may lead to remote code execution under local zone.
The first vulnerability affects firefox, and may affect mozilla as well. I have only tested
firefox under windows 2000 and windows XP so I'm not sure if this issue exists on other OS's.
The problem is that firefox stores its cache in a known directory, and some of the cached html
is stored in known files. If a victim visits the attackers website which includes malicious javascript
and then views the content of one of the cache files in local zone, the script will get executed and
the attacker will be able to compromise the victim's system. This vulnerability in mozilla can't be
abused as it is, but combined with a few other vulnerabilities the attacker could execute malicious
code on the victim's computer without having the victim do anything except visit his website (very
similar to the exploits in Internet Explorer).

The second vulnerability allows the attacker to modify the mime type by using the infamous NULL byte.
Mozilla by default uses the file extention name to decide how to show a local file. For example,
if a user requests file:///C:/blah.txt, Mozilla will show the contents of blah.txt, but if the user
requests file:///C:/blah then Mozilla will pop up a window asking the user if he/she wants to download
the file. By adding a NULL byte at the end of the filename, and the extention that you want Mozilla
to handle right after the filename, you can make Mozilla open file:///C:/blah as an html file.
Just like the vulnerability above, this can't be used alone to execute malicious code, the attacker
needs to combine the above vulnerability with this one to succeed.

Since the known cache file names have no extention by default on windows, if the attacker uses the NULL
byte bug, he/she can cause mozilla to show the contents of one of the cache files as an html file,
and therefore cause mozilla to execute whatever scripts that exist in the cache files.


The first vulnerability does not require an exploit.
On windows 2000, there are 3 cache files with known names. They are:

1. C:\Documents and Settings\Administrator\Application Data\Mozilla\Firefox\Profiles\default.nop\Cache\_CACHE_001_
        [ This cache file stores the http headers ]

2. C:\Documents and Settings\Administrator\Application Data\Mozilla\Firefox\Profiles\default.nop\Cache\_CACHE_002_
3. C:\Documents and Settings\Administrator\Application Data\Mozilla\Firefox\Profiles\default.nop\Cache\_CACHE_003_
        [ These 2 cache files store the html data ]

If we combine both vulnerabilities shown above we get something like this:

file://C:\\Documents and Settings\\Administrator\\Application Data\\Mozilla\\Firefox\\Profiles\\default.nop\\Cache\\_CACHE_002_%00.html

Mozilla will open this file without the %00.html, but it will treat it as an html file and won't pop up a download window.


Visit mozilla.org to check for updates.


- Mindwarper
- mindwarpermlsecurity.com
- http://mlsecurity.com