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HistoryJul 28, 2014 - 12:00 a.m.

Barracuda Networks Firewall 6.1.2 #36 - Filter Bypass & Exception Handling Vulnerability + PoC Video BNSEC-2398


Document Title:

Barracuda Networks Firewall 6.1.2 #36 - Filter Bypass & Exception Handling Vulnerability + PoC Video

References (Source):

Barracuda Networks Security ID (BNSEC): BNSEC-2398


Vulnerability Magazine:

View Video:

Solution #00006613
BNSEC-02398: Authenticated non- & persistent validation vulnerability in Barracuda Firewall v6.1.2

Release Date:


Vulnerability Laboratory ID (VL-ID):


Common Vulnerability Scoring System:


Product & Service Introduction:

The Barracuda Firewall goes beyond traditional network firewalls and UTMs by providing powerful network security,
granular layer 7 application controls, user awareness and secure VPN connectivity combined with cloud-based malware
protection, content filtering and reporting. It alleviates the performance bottlenecks in Unified Threat Management
(UTM) appliances through intelligent integration of on-premise and cloud-based technologies. While the powerful on-
premises appliance is optimized for tasks like packet forwarding and routing, Intrusion Prevention (IPS), DNS/DHCP
services and site-to-site connectivity; CPU intensive tasks like virus scanning, content filtering and usage
reporting benefit from the scalable performance and elasticity of the cloud.

(Copy o the Vendor Homepage: )

Abstract Advisory Information:

The Vulnerability Laboratory Team discovered a filter bypass and a persistent vulnerability in Barracuda Networks Firewall Appliance v6.1.0.016 Application.

Vulnerability Disclosure Timeline:

2013-09-26: Researcher Notification & Coordination (Benjamin Kunz Mejri)
2013-09-27: Vendor Notification (Barracuda Networks Security Team - Bug Bounty Program)
2013-09-30: Vendor Response/Feedback (Barracuda Networks Security Team - Bug Bounty Program)
2014-06-30: Vendor Fix/Patch (Barracuda Networks Developer Team) [Coordination: Dave Farrow]
2014-07-23: Public Disclosure (Vulnerability Laboratory)

Discovery Status:


Affected Product(s):

Barracuda Networks
Product: Firewall Appliance Web-Application - x100 x200 x300 x400 x500 x600 & Vx

Exploitation Technique:


Severity Level:


Technical Details & Description:

An input validation web vulnerability is detected in the official Barracuda Networks Firewall Appliance Web-Application.
The vulnerability allows an attacker (remote) to implement/inject own malicious persistent script codes (application side).

The vulnerability is located in the `VPN > Certificates` module when processing to request via POST to GET method manipulated
`cert_error` values through the secure appliance application exception-handling. The script code execution occurs in the main
header on top of the error message (exception-handling). The issue impact a persistent and non-persistent attack vector
because of the values can be exploited in the regular service GET method request in the referer on the client-side. The second
technique is to exploit by inject via POST method request to provoke an error (exception) with specific manipulated context.

The attacker moves to the certificates area and uploads even in the restricted mode 2 pem certs, he tampers the request and
exchange the upload path but drops also an invalid value to the name. The application will respond via GET and drops an unknown
error message in the exception-handling of the module. The attacker is able to change the referer and includes his own code to
the affected parameters. The result is a client-side execution in the first exception message body context.

Now the links in the main website will change to the error link with referer through application-side. The attacker is now
able to click the link or request the url to execute the code inside of the exception-handling contents`>Error message with
persistent attack vector.

The security risk of the persistent and non-persistent input validation vulnerability and fitler bypass is estimated as medium
with a cvss (common vulnerability scoring system) count of 5.7. Exploitation of the persistent web vulnerability requires low
user interaction and a local low privileged (restricted) web-application account. Successful exploitation of the vulnerability
results in application-side session hijacking (customers), account theft via persistent web attacks, persistent phishing,
persistent external redirects and persistent manipulation of affected or connected module context.

Request Method(s):
[+] POST & GET

Vulnerable Module(s):
[+] VPN > Certificates

Vulnerable Parameter(s):
[+] cert_error (contents:error)

Affected Module(s):
[+] Exception Handling - Error Message

Proof of Concept (PoC):

The input validation vulnerability in the exception-handling can be exploited by remote attackers with low privileged web-application user account
and low user interaction. For security demonstration or to reproduce the vulnerability follow the provided steps and information below to continue.

  1. You need to request the regular module …

  2. Provoke an error inside of the regular protected exception-handling via upload pem:

  3. After the redirect with the url to the error happened the attacker is able to change the exception input variable to execute own codes

PoC: Exception Handling - Error Message

<tr><td><table id="status_screen" class="status_screen"><tbody><tr><td><center><table class="status_module"
cellpadding="0" cellspacing="0"><tbody><tr><td><div id="error"><b class="outlinetop"><b class="outline1"></b>
<b class="outline2"></b><b class="outline3"></b><b class="outline4"></b></b><div
id="contents">Error: >"<[MALICIOUS INJECTED SCRIPT CODE!])"><<br>
</div><b class="outlinebottom"><b class="outline4"></b><b class="outline3"></b><b class="outline2"></b>
<b class="outline1"></b></b></div></td></tr></table></center></td></tr></table></td></tr><tr style="background-color:#D9F5FF;">
<td class="config_screen" valign="top" height="400" width="100%" ><table summary="Body" border="0" width="100%" ><tr ><td>
<table width=100% height=100% style="padding:2px" ><tr><td height=100%>
<table cellspacing=0 cellpadding=0 class=outlined>
<td class='tl'></td>
<td class='tm'></td>
<td class='tr'></td>

…/Barracuda Firewall Certificates - provoke unknown exception.htm
…/Barracuda Firewall Certificates.htm


Solution - Fix & Patch:

The remote web vulnerability can be patched by a secure parse and encode of the error message referer and exception-handling message
body context inside of the firewall certificate error exception-handling. Restrict the certificate error input but also the certificate
name value itself. Prepare a more secure invalid context exception without redisplay of the wrong encoded vpn cert inputs.

Barracuda Networks Appliance: Advanced >Firmware Updates Page

Security Risk:

The security risk of the persistent and non-persistent input validation web vulnerability with filter bypass is estimated
as high because of the location in the secure application exception-handling.

Credits & Authors:

Vulnerability Laboratory [Research Team] - Benjamin Kunz Mejri ( []

Disclaimer & Information:

The information provided in this advisory is provided as it is without any warranty. Vulnerability Lab disclaims all warranties,
either expressed or implied, including the warranties of merchantability and capability for a particular purpose. Vulnerability-
Lab or its suppliers are not liable in any case of damage, including direct, indirect, incidental, consequential loss of business
profits or special damages, even if Vulnerability-Lab or its suppliers have been advised of the possibility of such damages. Some
states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation
may not apply. We do not approve or encourage anybody to break any vendor licenses, policies, deface websites, hack into databases
or trade with fraud/stolen material.

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