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Date: Tue, 26 Apr 2016 16:09:45 +0200
From: Vulnerability Lab <>
Subject: Sophos XG Firewall (SF01V) - Persistent Web Vulnerability

Document Title:
Sophos XG Firewall (SF01V) - Persistent Web Vulnerability

References (Source):

ID: 5740075

Release Date:

Vulnerability Laboratory ID (VL-ID):

Common Vulnerability Scoring System:

Product & Service Introduction:
Sophos XG Firewall provides unprecedented visibility into your network, users, and applications right from the all-new control center. 
You also get rich on-box reporting and the option to add Sophos Firewall Manager and iView for centralized management and reporting 
across multiple Firewalls. Displays the real-time status of system performance, services, connections, and other system parameters. 
Green indicates everything is fine, orange indicates a warning, and red indicates something needs immediate attention. Each item is 
clickable to reveal additional details and graphs, as well as helpful system and network tools you can use for troubleshooting 
purposes such as ping, trace route, packet capture, command-line access, and much more.

(Copy of the Vendor Homepage: )

Abstract Advisory Information:
An independent vulnerability laboratory researcher discovered an application-side validation vulnerability in the official Sophos XG Firewall (SF01V) appliance web-application.

Vulnerability Disclosure Timeline:
2016-02-17: Researcher Notification & Coordination (Lawrence Amer)
2016-02-18: Vendor Notification (Sophos Security Team)
2016-04-25: Public Disclosure (Vulnerability Laboratory)

Discovery Status:

Affected Product(s):

Exploitation Technique:

Severity Level:

Technical Details & Description:
A persistent cross site scripting web vulnerability has been discoverd in the official Sophos XG Firewall (SF01V) appliance web-application.
The security issue allows remote attackers to inject own malicious script codes on the application-side of the affected service module.

The vulnerability is located in the `Protection  - Web Protection - Web Content Filter - General Configuration - Override Default Denied Message` module. 
Remote attackers and low privileged web-application user accounts are able to inject own malicious script code context as notification value of the 
Blocked Access Request. The data of the POST method request in the nody of message text, executes without a secure encoding or a restriction in the 
body of message in the web-application appliance. The persistent execution of the script code occurs in [Default Denied Message] that gets send by 
the appliances directly to users.

The security risk of the persistent validation vulnerability is estimated as high with a cvss (common vulnerability scoring system) count of 3.5. 
Exploitation of the persistent input validation web vulnerability requires a privileged web-application user account and low or medium user interaction. 
Successful exploitation of the vulnerability results in session hijacking, persistent phishing, persistent external redirects to malicious source and 
persistent manipulation of affected or connected application modules.

Request Method(s):
				[+] POST

Vulnerable Module(s):
				[+] Protection  - Web Protection - Web Content Filter - General Configuration - Override Default Denied Message

Vulnerable Parameter(s):
				[+] message body

Proof of Concept (PoC):
Persistent Web Vulnerability can be exploited by remote attackers with privileged web-application user account and low or medium user interaction.
For security demonstration or to reproduce the vulnerability follow the provided information and steps below to continue.

Manual steps to reproduce the vulnerability ...
1. goes to : Protection  > Web Protection > Web Content Filter> General Configuration
2. Choose the Override Default Denied Message input field 
3. Message HTML Input: [POC]
Note: '><iframe src="" onload=alert(document.cookie)<
4. After saving all users get it as default message of blocked requests as notification message
5. Successful reproduce of the vulnerability! 

<b><BR><font class=accessdeniedtextfont >This is a message from the IT Department. <BR><BR>The web site you are trying to access: '><iframe src="" onload=alert(document.cookie)<  <BR></font><font class=accessdeniedcategoryfont  >{url}</font><BR><font class=accessdeniedtextfont >is listed as a site within the category </font><font class=accessdeniedcategoryfont>{category}</font><BR><BR><font class=accessdeniedtextfont > Current Internet Access Configuration for you does not allow visiting sites within this category at this time.<BR><BR>If the website has been erroneously blocked,  please <a href="#" class="accessdeniedcategoryfont" onclick="callReevaluationFunction()">submit</a> it for re-evaluation.</font></b>

Solution - Fix & Patch:
The vulnerability can be patched by a secure parse and encode of the vulnerable input field context.
Encode all inputs and restrict the input by disallowing the usage of special chars.
Parse also the outgoing values for the user notification by the appliance service itself to prevent malicious attack scenarios.

Security Risk:
The security risk of the application-side input validation web vulnerability in the sophos xg firewall appliance web-application is estimated as medium. (CVSS 3.5)

Credits & Authors:
Lawrence Amer - ( )

Disclaimer & Information:
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or implied, including the warranties of merchantability and capability for a particular purpose. Vulnerability-Lab or its suppliers are not liable 
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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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