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With these threats in mind, we return to our objective: remotely obtaining root-privileged access without any authentication. The following section details our process for finding vulnerabilities in our targets.
Assessment Workflow This section covers the steps we took to identify vulnerabilities in our targets. Our intention was to identify potential attack surfaces and vulnerabilities that an advanced, targeted attacker might exploit to gain access to the system or other system specific resources. When necessary, automated tools were used, but more frequently, hands-on manual assessments of application components were performed to ensure that we conducted an accurate and complete review.
During the reconnaissance phase, we passively gathered as much information as we could about each device. We also downloaded and requested any open source code the manufacturer may have used.
Source code gave us insight into what libraries were used by each device. After initial reconnaissance, we began enumerating the default services available on each device.
We focused on network accessible services as we were interested in identifying remotely exploitable vulnerabilities. We documented the version number of each service, mapped each web application, and gathered network traffic. Next, we used what we learned during the service enumeration phase to identify vulnerabilities. When possible, we used shell access to the device during this phase to review source code and binaries used by network accessible services.
During the gaining access phase, we audited each device for vulnerabilities that granted us full access to our targets. After identifying vulnerabilities, we built proof-of-concept attacks PoCs. For example, we chained CSRF with CMDi to launch attacks that targeted authenticated users and abused their access to remotely compromise their device. In 12 of the 13 devices, we were able to achieve our goal of remote root-level access. The table below shows the types of vulnerabilities we identified in our targets. The following sections detail our targets, the security controls we encountered in a portion of our devices, and how we defeated each security control.
As a result, any user with network level access to this device can issue requests without authentication.
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This vulnerability could be used to enable or disable services, or perform other actions available through the web application. User creation follows a two-step process where the username is first stored in a database then retrieved and passed as an argument to the pdbedit system command. While this seems like a straightforward command injection vulnerability, we ran into a complication blacklist that prohibits usernames to contain certain special characters, i. With knowledge that the command processor used on the TeraStation is Bash, we could utilize built-in variables that can be used in place of the blacklisted characters.
Considering this, we used the following shell variables to build our final payload:. In the case of our exploit, this expands to nothing because we are not passing any parameters to the subshell. This payload will result in a user named ISEUserName being created and a telnet server being spawned as the root user listening on port The attacker can issue the following requests to first create the payload in the database and then trigger the command injection.
With the combination of an authentication bypass and a OS CMDi vulnerability, we demonstrate how attackers can circumvent some of the security controls Buffalo implemented on the TeraStation to obtain root privileges. This introduces the possibility for an uncontrolled format string vulnerability. In simple terms, ASLR randomizes the locations of segments in memory between different runs of a program.
As a result, it is difficult to exploit buffer overflow vulnerabilities to achieve code execution as the addresses of exploitable code are unpredictable. Fortunately, we were able to find an uncontrolled format string vulnerability that allowed us to disclose pointers saved on the call stack. In the Python script below, we use our format string vulnerability to disclose theses addresses then leverage this information to bypass ASLR, and develop a buffer overflow exploit that launches a shell using a combination of return oriented programming ROP and the well-known return-to-libc technique.
Try again when server restarts. Asus makes use of ASLR to guard against buffer-overflow attacks by randomizing the location in memory where system executables are loaded. We were able to use a format string vulnerability to circumvent this security control and effectively exploit a stack based buffer overflow we discovered on the device.
Its primary user interface is a web application. This device has functionality to support multiple user accounts, differentiating between standard users and administrators. The authentication workflow provides users with a session token as a cookie after the user supplies a correct username and password combination. The lack of authentication on certain API requests grants remote unauthenticated attackers the ability to bypass front-end only access controls on the F During our analysis of the F we needed to identify services that would grant us the ability to gain root shell access.
Although we could have mapped out the entire application and fuzzed each input field with common command injection payloads, we instead attempted to analyze each PHP file and determine which ones shell-out with user provided input. Instead of storing the PHP source files on the device as is common with PHP web applications, TerraMaster encrypts the source files making them unreadable by attackers with filesystem access in an attempt to hinder reverse engineering efforts.
However, because the encrypted files must be decrypted before they can be processed by the PHP interpreter, the decryption key must be stored on the NAS.theotercpergardmango.tk
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We extracted this key and decrypted each file manually with the following command. Attackers can use these attributes to achieve unauthenticated root system command injection. A sample payload is shown in the POST request below. Attackers may connect to this telnet server without authentication and execute arbitrary system commands. Drobo 5N2 The Drobo 5N2 is a NAS that allows users to install additional applications, administer the device, host additional web applications and databases, and serve as a network accessible storage device.
The 5N2 is unique in comparison to the other devices in this study as it does not feature any sort of web application by default. Instead, the primary user interface is a desktop application for Windows and macOS called Drobo Dashboard. NASd uses a custom protocol that attackers must reverse engineer in order to communicate with the service.
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Fortunately, the protocol can be understood after observing normal traffic between Drobo Dashboard and NASd. While this is ordinarily a poor form of authentication as the number can be found on the device itself and possibly elsewhere, the device also provides its serial number to anything that connects to port , also known as the stat port. Connections made to port , the cmd port, must include the serial number.
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For an in-depth look at the NASd protocol as well as a proof-of-concept program to interact with a Drobo 5N2, please refer to our Appendix. These applications, including the web application DroboAccess, had a number of vulnerabilities in them. DroboAccess has a command injection vulnerability that allows unauthenticated attackers to execute arbitrary system commands with root privileges. The following GET request shows a proof of concept request to start a telnet server. The security of the NASd protocol relies exclusively on the protocol being obfuscated and proprietary.
Sufficiently skilled adversaries can reverse engineer proprietary protocols, to then leverage the pervasive issue of missing authentication. After the attacker has successfully exploited missing authentication measures, they can install other applications. When we installed DroboAccess we discovered that there were many authenticated pages that shelled out to the underlying OS to issue commands that contain unsanitized user input granting us remote access with root level permissions.
As a result, traditional command injection techniques cannot be used. Fortunately for security researchers, zyshclient may also be used interactively.
After enabling telnet and logging into the NAS, zyshclient can be started resulting in a prompt similar to output shown below. After testing these functions, we determined that package executes Linux system commands. The output shown below contains the whoami command which indicates the process is executed as root. This request is also vulnerable to CSRF attacks, where an attacker can trick an authenticated user into issuing this request.
While assessing this device, we first analyzed how requests are routed then accessed each implemented route for vulnerabilities. In the figure below we illustrate the parameters used when issuing request to this endpoint. The controller for this request has a helper function for ensuring these parameters are either nil, or do not contain a blacklisted set of shell metacharacters characters that could be used to break out of the shell argument context.
The following characters are blacklisted by the Mi Router:. Using these characters, attackers can inject commands into the sns parameter. A sample GET request is shown in below.
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This character bypass shows how attackers could circumvent some of the security controls Xiaomi placed on the device. In addition to the vulnerability discussed above, this same endpoint is vulnerable to a command injection attack that is not restricted by the character blacklist at all.
This allows attackers to use any command injection payload, regardless of character set. As noted above, we also found other endpoints with programming logic errors that allowed us to circumvent the blacklist entirely. The primary user interface for this device is a web application, but a SOAP-based mobile application is also available.
Within either interface, an administrator may manipulate common network settings, view device logs, manage Quality of Service as well as various other settings. This device also appears to whitelist requests from its own IP address, allowing internal use of the API without managing authentication.
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