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Hardcoded Backdoor Found on Western Digital Storage Devices

Firmware updates released by Western Digital for its MyCloud family of devices address a series of security issues, including a hardcoded backdoor admin account.

Firmware updates released by Western Digital for its MyCloud family of devices address a series of security issues, including a hardcoded backdoor admin account.

The vulnerabilities were found in WDMyCloud firmware prior to version 2.30.165 and are said to affect devices such as MyCloud, MyCloudMirror, My Cloud Gen 2, My Cloud PR2100, My Cloud PR4100, My Cloud EX2 Ultra, My Cloud EX2, My Cloud EX4, My Cloud EX2100, My Cloud EX4100, My Cloud DL2100, and My Cloud DL4100.

Discovered by GulfTech security researcher James Bercegay, the security flaws could be exploited to achieve remote root code execution on the affected WD My Cloud personal cloud storage units (the device is currently the best-selling NAS (network attached storage) device on Amazon).

One of the most important security issues the researcher found was an unrestricted file upload vulnerability created by the “misuse and misunderstanding of the PHP gethostbyaddr() function,” the researcher says.

The vulnerable code in said file allows an attacker to define a remote auth server, which could be an attacker-controlled server. The result should fail if an invalid host is defined, but a series of bugs result in checks being skipped, eventually allowing an attacker to abuse the issue “to upload any file to the server that they want.”

While analyzing CGI binaries on the webserver, the security researcher discovered code where login functionality would specifically look for an admin user named “mydlinkBRionyg” and would accept the password “abc12345cba”.

The researcher then discovered that the backdoor could be turned into a root shell that would allow an attacker to execute any commands as root and gain control of the affected device. Damaging a vulnerable device would be extremely easy and would not require authentication.

“The triviality of exploiting this issues makes it very dangerous, and even wormable. Not only that, but users locked to a LAN are not safe either. An attacker could literally take over your WDMyCloud by just having you visit a website where an embedded iframe or img tag make a request to the vulnerable device using one of the many predictable default hostnames for the WDMyCloud such as “wdmycloud” and “wdmycloudmirror” etc.,” Bercegay explains.

In addition to the two critical vulnerabilities, the security researcher discovered a series of other dangerous issues as well in the WDMyCloud firmware. These bugs, however, are not deemed Critical, especially since some of them require authentication to be exploited.

The WDMyCloud web interface was found to lack an effective Cross site request forgery protection and exploitation of the issue is trivial, the researcher says. WDMyCloud is also plagued with a series of command injection issues. An attacker can abuse the language preferences functionality to cause denial of service to the web interface and can dump a list of all users, including detailed user information.

The researcher also discovered that the exact same mydlinkBRionyg backdoor account was found in the D-Link DNS-320L ShareCenter NAS device a while back, supposedly because both devices shared common firmware code. However, the issue was addressed in D-Link DNS-320L with firmware version 1.0.6, released in July 2014.

“It is interesting to think about how before D-Link updated their software two of the most popular NAS device families in the world, sold by two of the most popular tech companies in the world were both vulnerable at the same time, to the same backdoor for a while. The time frame in which both devices were vulnerable at the same time in the wild was roughly from early 2014 to later in 2014 based on comparing firmware release note dates,” Bercegay notes.

The researcher reported all these vulnerabilities to the vendor in June 2017. Firmware release 2.30.174 should address all of these issues.

Related: Multiple Zero-days Disclosed in Western Digital NAS Storage Devices

Related: Western Digital Patches Vulnerabilities in “My Cloud” Products


Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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