Serious vulnerability discovered in D-Link routers

UPDATE: patch available for users on D-Link support pages

In November 2018, Greenbone discovered a serious security vulnerability in D-Link routers and drew the company’s attention to it. The vulnerability is easy for hackers to exploit and allows unauthorised access to networks. There is now a patch available from the vendor. Greenbone has been offering its customers a vulnerability test (NVT) as part of its daily security feed since the end of last year.

Routers are pivotal to both home and business networks. They establish an Internet connection for connected laptops and PCs, and also for smart home and industrial applications. But even though so many components of a network converge here, router security is not always adequate. For example, last year, researchers at the American Consumer Institute found known vulnerabilities in 83 percent of the routers it examined as part of the study. Hackers can use these vulnerabilities to gain access to the device itself and therefore to the entire network. In total, the researchers counted more than 30,000 separate vulnerabilities – 7 percent of which represented a critical risk, while 21 percent were high risk.

Design errors make the DWR and DAP models vulnerable to attack

In addition to the already known vulnerabilities in routers, new ones are being found on a near constant basis. In November 2018, Greenbone security researchers found a serious vulnerability in various D-Link routers, particularly the DWR and DAP models. Described as an “Unauthenticated Remote Code Execution”, the vulnerability is a security hole where an attacker can execute commands on the router without any authentication. In the case of the D-Link routers, a hacker can even obtain full administrative rights. It is very likely that the NIST (National Institute of Standards and Technology) will award the highest possible CVSS rating (Common Vulnerability Scoring System) of 10.0.

The cause is probably a design flaw. In the devices we tested, we found an executable file called “EXCU_SHELL” that can be selected from the web browser using a so-called GET request. This is responsible for some useful (yet harmless) operations, such as displaying information about the installed firmware. But if you adjust some of the file’s parameters, it is possible to insert and execute arbitrary commands.

Access to routers without authentication possible

D-Link is one of the top vendors in the global wireless router market and was the market leader in 2017, with a market share of 24.1 percent.

But it’s not just the potential number of customers that could be impacted that make this vulnerability significant.  According to the CVSS basic score calculator, the severity of the vulnerability is high and relatively easy to exploit. The “EXCU_SHELL” file is not password-protected and hackers can therefore access the router and the associated network without authentication. Once infiltrated, all incoming and outgoing Internet traffic can be viewed, modified and controlled. It may even be possible for hackers to spread malware.

With smart home and IoT technologies, such vulnerabilities cause considerable damage. Hackers can open the door to critical infrastructures, such as health care facilities or energy suppliers.

D-Link publishes security update on March 19, 2019

Greenbone reported the vulnerability to D-Link last November. The manufacturer was responsive throughout the process and asked us to take over the CVE application. The D-Link website now provides information for customers and a patch has been made available.

After more than 90 days that have passed since the vulnerability was discovered – the deadline expired on February 11, 2019 – we were acting in accordance with Responsible Disclosure and published all available information to protect users. For Greenbone customers, the gap has been visible via the daily security feed since November 2018.

Manufacturers must act

Given the sheer number of security vulnerabilities on routers, closing the D-Link gap is certainly just a drop in the ocean. While the number of vulnerabilities is intimidating, placing your head in the sand is not an option. Focus must be placed on persuading (or, in some cases, forcing) as many manufacturers as possible to secure their routers.