Serious flaws in Western Digital My Cloud NAS devices allow attackers to fully control them

Researchers discovered serious issues in Western Digital My Cloud NAS that can be exploited by attackers to gain root control of the affected devices.

Western Digital Corporation network-attached storage owners were warned of Critical flaws in Western Digital NAS boxes of the My Cloud NAS line could be exploited by remote attackers to gain remote control of the affected devices.

The attackers can combine the flaws to steal sensitive data or to exploit flawed devices in lateral movements.

“By combining the vulnerabilities documented in this advisory an attacker can fully compromise a WD My Cloud device. In the worst case one could steal sensitive data stored on the device or use it as a jump host for further internal attacks.”

“SEC Consult recommends not to attach WD My Cloud to the network until a thorough security review has been performed by security professionals and all identified issues have been resolved.” reads the advisory published by SCVL.

The affected products belong to Western Digital MyCloud NAS devices, including DL4100, EX4, EX2 Ultra and PR2100. The full list of flawed devices is available online.

The attackers can trigger the flaw to bypass logins, insert commands, upload files without permission, and gain control of boxes.

“This is a serious vulnerability, as the chances for the device to be fully compromised is very high,” explained the SEC Consult Vulnerability Lab (SCVL).

The flaws have been reported by SCVL experts to Western Digital on Jan. 18, 2016 and publicly disclosed the flaw March 7, 2017. Another group of experts from the security firm Exploitee.rs have discovered the vulnerabilities and publicly disclosed them.

The flaws discovered by the experts include a command injection vulnerabilities, a stack-based buffer overflow bug, and a cross-site request forgery flaw.  As anticipated, by combining the exploitation of the cross-site request forgery issue with a command injection vulnerability the attacker can gain root access of the affected device and fully compromise it.

“The (cross-site request forgery flaw) can be combined with a command injection vulnerability to gain complete control (root access) of the affected device,” explained the advisory issued by the SCVL.

As of this writing, Western Digital has not provided any information regarding the vulnerabilities or supplied software updates to fix the reported bugs.

According to the researchers at Exploitee.rs, in December, the expert Steve Campbell discovered two command injection flaws in Western Digital MyCloud NAS (CVE-2016-10107 & CVE-2016-10108) that were patched by the company in the same month, but according to Exploitee.rs the patches did not fix the problems and introduced a new Login Bypass vulnerability.

The Exploitee.rs researcher Zenofex who analyzed the Login Bypass issue discovered a wrong implementation of the user authentication mechanism when the Secure Shell (SSH) access was enabled. The login check leverage on cookies that can be crafted by an attacker to bypass the login process.

“The above code contains a function called “login_check”, this function is used by all of the backend PHP scripts and is used to verify pre-authenticated users. The above code has two paths, one which involves checking the session values for “username” and “isAdmin” and another (if the prior fails) attempts to complete the same process but with cookies.” explained Zenofex.

“Because cookies are supplied by the user, the requirements that the scripts are looking for can be met by the attacker. The above process for sessions and cookies is summed up as follows.

“username” variable is set and is not empty – User is logged in as a normal privileged user.

“isAdmin” variable is set to 1 – User is logged in as an administrator.

This means that any time there is a login check within the PHP scripts, an attacker is able to bypass the check by supplying 2 specially crafted cookie values.”

The experts at Exploitee.rs have found 85 security issues tied to Western Digital My Cloud NAS devices

My Cloud users can contact the Customer Service for any question and to receive support. It is important that My Cloud NAS devices are configured to enable automatic firmware updates.

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Pierluigi Paganini

(Security Affairs – Western Digital My Cloud devices,  hacking)