KL-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):~#


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KoreLogic, Inc. and are licensed under a Creative Commons
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