Teracue ENC-400 – Command Injection / Missing Authentication
Introduction ============ Multiple vulnerabilities were identified within the Teracue ENC-400, including pre-authenticated remote code authentication. While the vendor has released updated firmware after these issues were identified, they are not all resolved with the latest version of the firmware. Product ======= The Teracue ENC-400 is accessible over an HTTP interface, which allows device configuration (including setting passwords or video stream destinations and servers). The vendor describes the device as follows: This HD/SD H.264 fanless video encoder is able to deliver multiple streams in multiple bitrates and protocols to multiple destinations. [1] These issues affect firmware versions v2.56 or below. Note that the latest version of firmware, v2.57, does not adequately resolve all identified issues. Specific notes have been added to issues in the Technical Details section. Technical Details ================= 1) Command injection in login form ---------------------------------- CVE-2018-20218 The login form passes user input directly to a shell command without any kind of escaping or validation. In the file /usr/share/www/check.lp: #!/usr/bin/env cgilua.cgi <% local pass = cgilua.POST.password local com1 = os.execute("echo \'"..cgilua.POST.password.."\' | (su -c /bin/true)") An attacker is able to perform command injection using the "password" parameter displayed on the login form. An example "password" to bypass this authentication would be: f' > /dev/null # It is also possible for an attacker to simply execute code directly on the server. * Resolution Status * While this instance of remote code execution has been resolved, the resolution does not protect the entire codebase. In /usr/share/www/web/system_password.lp: local oldpass = cgilua.POST.oldpass local newpass = cgilua.POST.newpass local com1=os.execute("echo '"..oldpass.."' | (su -c 'echo '"..oldpass.."' | (su root -c '/bin/true') > /dev/null 2>&1 ; echo $?')") This allows an authenticated user to execute commands without knowing the existing password. This is particularly important given the insufficient resolution of CVE-2018-20219 (issue 2). 2) Hard-coded authentication token ---------------------------------- CVE-2018-20219 After successful authentication, the device sends an authentication cookie to the end user such that they can access the devices web administration panel. This token is hardcoded to a string in the source code. In the file /usr/share/www/check.lp: cookies.sethtml("AuthByPasswdENC400","Teracue:dGFpOfrtmR1bW1thrf5dGV4nhyxxdA==",{path='/'}) (Note: Line may be slightly different in different firmware versions, though the token is still the same). By simply setting this cookie in a browser, an attacker is able to maintain access to every ENC-400 device without knowing the password. Even if a user changes the password on the device, this token is static and unchanged. This results in an authentication bypass. * Resolution Status * While this cookie is now dynamically generated, the latest code generates cookie values from the current time in seconds. In the file /usr/share/www/check.lp: math.randomseed(os.time()) local cookie_value=RandomVariable(30) An attacker is able to trivially bypass authentication simply by knowing the approximate time of the last successful authentication. 2) Missing authentication on sensitive endpoints --------------------------------------------------------------------------------- CVE-2018-20220 While the web interface requires authentication before it can be interacted with, a large portion of the HTTP endpoints are missing authentication. The "/configuration.xml" file, for example, includes all information required to access a video stream, such as the IP and port information, and any encryption information if specified. * Resolution Status * No verification was performed as to whether this issue was appropriately resolved, or whether other files may be left unprotected. Disclosure Timeline =================== Attempts to contact vendor begin: August 30, 2018 Vendor contacted: September 7, 2018 Vendor acknowledges issues: October 23, 2018 Initial fixes released for testing: December 4, 2018 Response indicating insufficient fixes: December 4, 2018 Public firmware release: February 13, 2019 References ========== [1] https://www.teracue.com/en/iptv-products/encoding |