Bug: Firefox: serious cookie stealing / same-domain bypass vulnerability ( Ascii Version )

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Firefox: serious cookie stealing / same-domain bypass vulnerability

Published
Credit
Risk
2007.02.20
Michal Zalewski
Medium
CWE
CVE
Local
Remote
CWE-264
CVE-2007-0981
No
Yes

CVSS Base Score
Impact Subscore
Exploitability Subscore
7.5/10
6.4/10
10/10
Exploit range
Attack complexity
Authentication
Remote
Low
No required
Confidentiality impact
Integrity impact
Availability impact
Partial
Partial
Partial

There is a serious vulnerability in Mozilla Firefox, tested with 2.0.0.1,
but quite certainly affecting all recent versions.

The problem lies in how Firefox handles writes to the 'location.hostname'
DOM property. It is possible for a script to set it to values that would
not otherwise be accepted as a hostname when parsing a regular URL -
including a string containing \x00.

Doing this prompts a peculiar behavior: internally, DOM string variables
are not NUL-terminated, and as such, most of checks will consider
'evil.com\x00foo.example.com' to be a part of *.example.com domain. The
DNS resolver, however, and much of the remaining browser code, operates on
ASCIZ strings native to C/C++ instead, treating the aforementioned example
as 'evil.com'.

This makes it possible for evil.com to modify location.hostname as
described above, and have the resulting HTTP request still sent to
evil.com. Once the new page is loaded, the attacker will be able to set
cookies for *.example.com; he'll be also able to alter document.domain
accordingly, in order to bypass the same-origin policy for XMLHttpRequest
and cross-frame / cross-window data access.

A quick demonstration is available here:

http://lcamtuf.dione.cc/ffhostname.html

If you want to confirm a successful exploitation, check Tools -> Options
-> Privacy -> Show Cookies... for coredump.cx after the test; for the demo
to succeed, the browser needs to have Javascript enabled, and must accept
session cookies.

The impact is quite severe: malicious sites can manipulate authentication
cookies for third-party webpages, and, by the virtue of bypassing
same-origin policy, can possibly tamper with the way these sites are
displayed or how they work.

Regards,
/mz
http://lcamtuf.coredump.cx/

See this note in TXT Version

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Ascii Version