CVE-2016-20017: D-Link DSL-2750B Devices Command Injection Vulnerability

CVE-2016-20017 is a command injection vulnerability in D-Link DSL-2750B devices. It allows a remote attacker with no authentication to inject and run operating-system commands through the login.cgi interface via the cli parameter. Because these devices often sit at the network edge as consumer or small-office routers, successful exploitation can give an attacker full control of the gateway, enabling traffic interception, lateral movement, or persistent access. Confirm all product and firmware details against the vendor advisory before acting.

The weakness is classified as CWE-77 (Improper Neutralization of Special Elements used in a Command). Organizations still running this hardware should treat the issue as high priority and follow CISA guidance to apply vendor mitigations or discontinue use if none are available.

How it works

Command injection occurs when user-supplied input is passed to a system shell or command interpreter without proper sanitization. In this case the login.cgi endpoint accepts a cli parameter that is not adequately filtered. An unauthenticated remote attacker can craft a request that appends additional shell commands to the intended operation. Those commands execute with the privileges of the web service process, which on many embedded routers is sufficient to reconfigure the device, open reverse shells, or install persistent malware. Exact request syntax and payload details are not provided here; defenders should rely on the vendor advisory and public technical analyses rather than inventing exploit code.

Am I affected? How to find it in your systems

D-Link DSL-2750B units are typically deployed as DSL gateways in homes, branch offices, or small businesses. Inventory steps include:

• Query network management systems, DHCP leases, and ARP tables for devices advertising the model string “DSL-2750B” or the corresponding OUI.
• Scan the management interfaces (commonly ports 80/443 or the vendor’s proprietary ports) and examine HTTP banners or the login page for the model identifier.
• Check firmware version strings reported by the device’s web UI or SNMP; any version that has not received the vendor’s remediation must be treated as vulnerable until confirmed otherwise.
• Review web-server access logs for unusual requests to login.cgi that contain unexpected characters in the cli parameter (semicolons, pipes, backticks, etc.).
• Look for anomalous outbound connections originating from the router itself, unexpected process lists, or configuration changes that cannot be attributed to legitimate administrators.

Because exact affected firmware revisions are not listed in the supplied facts, always cross-check the current vendor advisory.

How to remediate

The primary remediation is to apply the vendor-supplied update or mitigation instructions for the DSL-2750B. If the vendor has declared the product end-of-life and no fix exists, CISA requires that the device be discontinued and replaced. After patching or replacement:

• Change all default and previously used administrative credentials.
• Disable remote management interfaces if they are not strictly required, or restrict them to a management VLAN or VPN.
• Ensure the device firmware is obtained only from official D-Link channels and verify integrity where possible.
• Re-baseline configuration and enable any available logging of administrative actions.

Document the change and re-scan the network to confirm the vulnerable instance is gone.

If you can't patch immediately

Until a permanent fix or replacement is in place, reduce exposure with compensating controls:

• Segment the device onto an isolated network segment that cannot reach critical internal assets; block all inbound traffic from untrusted networks to the management ports.
• Place a web application firewall or reverse-proxy rule in front of the login.cgi endpoint that rejects requests containing shell metacharacters in the cli parameter (virtual patching).
• Disable the affected web management feature entirely if the device can still be administered via a local console or out-of-band method.
• Increase monitoring: alert on any HTTP request to login.cgi that includes the cli parameter, and watch for unexpected DNS, HTTP, or reverse-shell traffic leaving the router.
• If the device is no longer needed, power it off and remove it from the network immediately.

These measures buy time but do not eliminate the underlying vulnerability.

If your data may have been exposed

Actively exploited edge-device vulnerabilities frequently lead to full network compromise and subsequent data theft. If logs or other indicators suggest this CVE was used against your environment, treat the incident as a potential breach: isolate affected systems, preserve forensic evidence, and follow your incident-response plan. As a quick additional check, you can run a free exposure scan of your email addresses against known breach data sets to determine whether credentials or personal information have already appeared in public dumps.