Unauthenticated Command Injection Flaw Exposes D-Link VPN Routers to Attacks

D-Link is working on releasing firmware updates to address two command injection vulnerabilities that affect multiple VPN router models.

Security researchers at Digital Defense identified a total of three vulnerabilities that affect several D-Link VPN routers, including authenticated and unauthenticated command injection flaws, and an authenticated crontab injection issue.

Initially discovered in DSR-250 routers running firmware version 3.17, the vulnerabilities were confirmed to affect other devices as well, namely D-Link DSR-150, DSR-250, DSR-500, and DSR-1000AC VPN routers running firmware versions 3.17 and earlier.

The most important of these bugs could allow an unauthenticated attacker able to access the “Unified Services Router” web interface over LAN or WAN to inject arbitrary commands that are executed with root privileges. The attacker would need to send specially crafted requests to trigger the flaw.

“The following lua cgi actions, which are accessible without authentication, execute a lua library function which passes user-supplied data to a call to os.popen() as part of a command intended to calculate a hash: /platform.cgi?action=duaAuth, /platform.cgi?action=duaLogout,” D-Link explains in an advisory.

According to Digital Defense, exploitation of this vulnerability could essentially allow an unauthenticated attacker to gain complete control of the router. Thus, they could intercept and modify traffic, cause a denial of service (DoS) condition, or set up for further attacks, targeting additional assets.

Similarly, the second vulnerability could allow an attacker to inject commands that would be executed with root privileges. Unlike the first bug, however, this one requires authentication.

“The Lua CGI, which handles requests from the ‘Package Management’ form in the ‘Unified Services Router’ web interface, has no server-side filtering for the multi-part POST parameters payload, which are passed to os. execute () functions intended to move the uploaded file to another directory,” D-Link says.

The third bug could allow an authenticated user to inject arbitrary CRON entries that will then be executed as root.

According to D-Link, a fix won’t be released for this vulnerability, for this generation of products. The company explains that an attacker looking to exploit this bug would first need to find a way to access the device and upload a configuration file.

Thus, D-Link considers that, once the firmware release that patches the first two issues is available, the third vulnerability is low-impact and does not require addressing.

The company plans on making the patched firmware available for its users in mid-December. Until then, however, users can download the available hotfixes, which are considered beta firmware releases.

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