CVE-2026-0625: Active Exploitation of Legacy D-Link Routers

Imagine a small business owner in 2026. Their office relies on a trusty, older D-Link router that hasn't been touched in years. It works, so why change it?

While the office is closed, that router is "interviewing" for a new job. Without any clicks or password entries, it is being recruited into a global botnet. This isn't a movie; it’s the real-world reality of CVE-2026-0625, a critical RCE vulnerability currently being exploited across the globe. Security telemetry from global monitoring projects confirms that thousands of legacy routers are being scanned and exploited automatically every day.

Silent exploitation of a legacy D-Link router via CVE-2026-0625 during off-hours


Attack Flow at a Glance

The following flow shows, step by step, how a single unauthenticated internet request can quietly transform a forgotten router into part of a criminal botnet.

[ Internet Scanning Bots ] (Automated mass scanners searching the web) ⬇️

[ Legacy D-Link Router Found ] (Public IP identifies a vulnerable gateway) ⬇️

[ Web Request Sent to dnscfg.cgi ] (Unauthenticated HTTP access attempt) ⬇️

[ No Password Requested ] (The endpoint performs no authentication checks at all) ⬇️

[ Router OS Processes Input ] (User data is passed directly to the router's internal Linux shell) ⬇️

[ The "Semicolon" Weapon ] (Malicious command injected via ; separator) ⬇️

[ Root Execution ] (Command runs with full Administrator privileges) ⬇️

[ Malware Deployment ] (Remote payload is downloaded and authorized) ⬇️

[ Persistence Established ] (Startup files modified to survive reboots) ⬇️

[ Full Botnet Integration ] (Router joins a global army for DDoS, spying, and hijacking)

In simple terms: The router is never “hacked” interactively — it blindly follows instructions from the internet because it was never designed to defend itself.

The Real-World Scenario: A 3:00 AM Takeover

The attack doesn't start with a hacker typing your name. It starts with an automated script—a "bot"—that is constantly scanning every corner of the internet for a way in.

Phase 1: The Automated Scout

At 3:00 AM, the bot finds the office IP. It notices the device is a legacy D-Link gateway and sends a simple web request to the dnscfg.cgi endpoint. The router responds immediately. Because the endpoint was never designed to be exposed to the internet, it performs no authentication checks. It simply waits for instructions.

Phase 2: The Silent Injection

The bot sends a "chained" command. To the router, it looks like a simple request to update its DNS settings (the "phonebook" it uses to find websites).

  • The Purpose of DNS Settings: Every router has a setting called "Primary/Secondary DNS." Its job is to tell the router which server to ask when you type a name like mybank.com. By default, your ISP handles this, but the dnscfg.cgi library allows these settings to be changed for better speed or privacy. Attackers target this because if they can change your DNS, they can quietly redirect your internet traffic to their own fake servers.

  • The Trick: The bot hides a secret instruction behind a semicolon (;).

  • The Vulnerability: The router fails to treat user input as plain text and instead passes it directly to the router’s internal operating system (a lightweight version of Linux) as a command. In other words, the router mistakes user-provided text for trusted system instructions.

  • The Logic: In the router’s OS, that semicolon means: "Finish task A, then start task B." While the router thinks it is just updating its DNS to 8.8.8.8, it is actually being told to download a hidden file and run it with full "root" privileges (the highest level of control on the device).

Phase 3: The Persistent Soldier

Within seconds, the router is compromised. The malware it just downloaded rewrites the router's startup instructions. Even if the owner reboots the device the next morning, the malware re-installs itself. The "ghost" is now part of the machine.

Why This Matters to You

Once the router is recruited, the attacker doesn't just "own" the router—they own the gateway to your digital life.

  • DNS Hijacking: When you type mybank.com, the router can silently send you to a perfect replica site owned by the hacker.

  • The Botnet Soldier: Your router's processing power is used to launch massive DDoS attacks against others.

  • Invisible Spying: Because these devices sit below traditional security tools, their compromise often goes undetected for years.

The "Unpatchable" Truth

D-Link officially declared these models End-of-Life (EoL) in 2020. This means there are no security patches, no firmware updates, and no vendor support—now or in the future.

Confirmed vulnerable models (End-of-Life, no patches):

  • DSL-526B

  • DSL-2640B

  • DSL-2740R

  • DSL-2780B

How to Fix CVE-2026-0625 (What Actually Works)

The Only Permanent Fix

Replace the legacy D-Link router with a modern, supported gateway. This is the only action that fully removes the vulnerability. Any device that no longer receives security updates should be treated like an unpatched operating system.

Temporary Risk Reduction (Not a Fix)

If replacement is not immediately possible, the steps below may reduce exposure but do not eliminate the vulnerability:

  • Disable Remote / WAN Management to prevent internet-wide scanning.

  • Audit DNS settings for unauthorized third-party IP addresses.

Final Verdict The legacy D-Link crisis is a global reminder: In 2026, the strongest defense isn't a louder alert—it's Data Resilience. When hardware is abandoned by the vendor but still connected to your life, recovery isn't measured in days—it's measured in the safety of your entire network.

Related Intelligence: If you missed our previous alert on critical browser security, read our breakdown of the Google Chrome Emergency Patch (December 2025).

Stay Technical. Stay Human. Stay Safe. — The ZyberWalls Research Team

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