CVE-2019-16057

CVE-2019-16057: Remote Command Injection in D-Link DNS-320 login_mgr.cgi

AI-generated analysis based on the vulnerability data on this page.

Summary

The login_mgr.cgi script in D-Link DNS-320 Network Attached Storage (NAS) firmware through version 2.05.B10 is vulnerable to remote command injection. An unauthenticated attacker on the network can exploit this flaw to execute arbitrary operating-system commands with root privileges on the device.

Background

D-Link DNS-320 is a consumer-grade NAS device designed for home and small-office file sharing. The device exposes a web-based management interface that includes the login_mgr.cgi endpoint for authentication handling. In affected firmware versions, this endpoint does not adequately sanitize user-controlled input before passing it to shell-execution contexts, creating a direct path from the HTTP request to the underlying operating system.

Root Cause — CWE-78

This vulnerability is classified under CWE-78: Improper Neutralization of Special Elements used in an OS Command (OS Command Injection).

The root cause is that login_mgr.cgi constructs operating-system commands using attacker-supplied input without proper input validation, escaping, or parameterization. When a request reaches the CGI script, the application logic treats portions of the HTTP parameters as literal shell tokens rather than as data, allowing metacharacters (such as command separators, backticks, and pipe operators) to alter the intended command flow and inject arbitrary instructions.

Impact

The CVSS v3 score of 9.8 (CRITICAL) reflects the severe, unauthenticated nature of this flaw:

Exploitation Walkthrough (Defensive Context)

Ethics Caveat: The following walkthrough is provided for defensive awareness, detection tuning, and incident-response context only. It does not contain weaponized exploit code. Unauthorized access to systems you do not own or operate is illegal under most jurisdictions.

1. Reconnaissance: An attacker identifies a D-Link DNS-320 device exposed to the internet or a local network segment (commonly via TCP ports 80/443 or passive service-discovery broadcasts).
2. Parameter Analysis: The attacker sends HTTP requests to the login_mgr.cgi endpoint and observes how query parameters or POST body fields are processed.
3. Injection Testing: By injecting shell metacharacters into login fields (for example, using semicolons, backticks, or pipe operators), the attacker observes anomalous response timing, error messages, or side effects indicating command execution.
4. Command Confirmation: The attacker issues a benign command (such as a DNS lookup or time-delay) to confirm the injected command is executed by the underlying OS.
5. Post-Exploitation Risk: With root shell access, the attacker can harvest stored credentials, exfiltrate files, install persistent firmware implants, pivot into the internal network, or use the device as a botnet node.

Affected and Patched Versions

Because the DNS-320 is an older device, D-Link has not publicly released a firmware patch specifically for this CVE. Defenders should treat all DNS-320 units running firmware ≤ 2.05.B10 as permanently vulnerable.

Remediation

1. Immediate — Remove Exposure:

   • Disconnect the device from the internet.
   • If internal use is required, place it behind a firewall that restricts access to trusted management IP ranges only.
   • Disable remote/cloud access features on the device if available.

2. Compensating Controls:

   • Segment the NAS onto an isolated VLAN with no outbound internet access.
   • Apply strict ingress rules on the management interface (TCP/80, TCP/443) so only designated admin hosts can reach it.
   • Monitor proxy / IDS logs for requests to login_mgr.cgi containing shell metacharacters.

3. Long-Term — Replace the Device:

   • Given the end-of-life status and lack of patches, the safest and most compliant remediation is to retire the DNS-320 and migrate data to a currently supported NAS platform with active security maintenance.

Detection

• Network Signatures: Monitor for inbound HTTP requests to /login_mgr.cgi with abnormal query parameters, especially those containing shell tokens (;, |, &&, `, $(), |bash, etc.).
• Behavioral Telemetry: Unexpected DNS queries, outbound connections, or file-system activity from the NAS process context are strong indicators of successful exploitation.
• Log Analysis: If the device supports any form of request logging (or if traffic is captured at a reverse proxy / WAF), correlate login_mgr.cgi access with anomalous response codes or payload sizes.
• Vulnerability Scanning: Use authenticated or unauthenticated network scanners that include this CVE to confirm exposure during routine assessments.

Assessment

With an EPSS score of 0.8721 (placing it in the 97.7th percentile), this CVE is one of the most actively exploited weaknesses in the catalog. Its inclusion in the CISA Known Exploited Vulnerabilities (KEV) list since April 2022 confirms that threat actors routinely target internet-facing DNS-320 devices.

Key lessons:

1. Legacy IoT/NAS devices must not face the internet. A consumer-grade device from 2010–2015 without ongoing patch support becomes a liability the moment it is exposed to a hostile network.
2. Input validation is foundational. CWE-78 remains a top-ten recurring vulnerability class because developers continue to pass user input directly to shell execution primitives. Every parameter entering a system boundary must be treated as hostile until proven otherwise.

References

• https://blog.cystack.net/d-link-dns-320-rce/
• https://www.ftc.gov/system/files/documents/cases/dlink_proposed_order_and_judgment_7-2-19.pdf
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-16057