CVE-2020-25506: D-Link DNS-320 Firmware RCE Vulnerability

CVE-2020-25506 Overview

CVE-2020-25506 is a command injection vulnerability affecting the D-Link DNS-320 network-attached storage (NAS) device running firmware version 2.06B01 Revision Ax. The flaw resides in the system_mgr.cgi component and allows unauthenticated remote attackers to execute arbitrary operating system commands. CISA has added this vulnerability to its Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. The vulnerability is tracked as [CWE-78] (Improper Neutralization of Special Elements used in an OS Command).

Critical Impact
Unauthenticated network attackers can execute arbitrary commands as the device's privileged user, leading to full takeover of the NAS, theft of stored data, and use of the appliance as a foothold inside enterprise networks.

Affected Products

D-Link DNS-320 NAS (hardware Revision Ax)
D-Link DNS-320 firmware version 2.06B01
End-of-life DNS-320 deployments still exposed to untrusted networks

Discovery Timeline

2021-02-02 - CVE-2020-25506 published to NVD
2025-11-07 - Last updated in NVD database

Technical Details for CVE-2020-25506

Vulnerability Analysis

The DNS-320 web management interface exposes the system_mgr.cgi script, which processes administrative parameters submitted over HTTP. The script passes user-supplied input into a shell context without sufficient sanitization or escaping. Attackers can inject shell metacharacters such as ;, |, &, or backticks to append arbitrary commands to the intended invocation.

Because the CGI binary runs with elevated privileges on the embedded Linux operating system, injected commands execute with administrative rights. Successful exploitation produces full remote code execution over the network with no authentication, no user interaction, and low attack complexity. EPSS data places this vulnerability among the highest-likelihood exploitation candidates tracked publicly.

Root Cause

The root cause is improper neutralization of OS command elements [CWE-78] in the system_mgr.cgi request handler. Parameters parsed from the HTTP request flow directly into a system()-style call without allowlisting, parameter binding, or quoting. This pattern is common in legacy embedded web stacks that concatenate shell strings to invoke helper utilities.

Attack Vector

The attack vector is purely network-based. An attacker crafts an HTTP request targeting system_mgr.cgi on the DNS-320 management interface and embeds shell metacharacters within a vulnerable parameter. When the request is processed, the injected payload runs in the device shell. Exposed DNS-320 units reachable from the internet have been mass-scanned and conscripted into botnets, consistent with CISA KEV listing.

The vulnerability manifests in the CGI parameter parsing logic. Refer to the D-Link Security Advisory SAP10183 and the public GitHub Gist proof-of-concept for request-level technical details.

Detection Methods for CVE-2020-25506

Indicators of Compromise

HTTP requests to /cgi-bin/system_mgr.cgi containing shell metacharacters such as ;, |, &, `, or $() in query parameters or POST bodies
Outbound connections from DNS-320 devices to unfamiliar IP addresses, particularly to known botnet command-and-control infrastructure
New or modified files in writable filesystem paths on the NAS, including unexpected shell scripts or binaries downloaded via wget or curl
Unexpected processes spawned by the web server parent process, such as sh, busybox, or telnetd

Detection Strategies

Inspect web server and reverse proxy logs for requests to system_mgr.cgi originating from external or unauthorized internal sources
Deploy network IDS/IPS signatures that flag command injection patterns in HTTP traffic destined for D-Link NAS management ports
Correlate authentication-less administrative URL requests with subsequent outbound traffic spikes from the same device

Monitoring Recommendations

Place legacy NAS appliances on isolated VLANs with full packet capture to retain forensic evidence of CGI exploitation attempts
Forward firewall, DNS, and proxy logs covering NAS devices into a centralized analytics platform for cross-source correlation
Alert on any management plane access to DNS-320 devices from outside a defined administrative subnet

How to Mitigate CVE-2020-25506

Immediate Actions Required

Remove DNS-320 management interfaces from any internet-exposed network segment without delay
Inventory all D-Link DNS-320 units and confirm firmware revisions against D-Link Security Advisory SAP10183
Treat any DNS-320 that has been internet-reachable as potentially compromised and perform a forensic review before reuse
Plan decommissioning of end-of-life DNS-320 hardware in favor of supported storage platforms

Patch Information

D-Link classifies the DNS-320 as an end-of-life product. The vendor advisory SAP10183 and the broader D-Link Security Bulletin direct customers to retire the device, since no security-supported firmware addresses CVE-2020-25506 for affected revisions. Organizations bound by CISA directives must remediate per the CISA Known Exploited Vulnerabilities Catalog entry.

Workarounds

Block inbound HTTP and HTTPS access to the DNS-320 web interface at the perimeter firewall and on internal segmentation boundaries
Restrict management plane access using ACLs that allow only a hardened administrative jump host
Disable remote administration features and any UPnP or port-forwarding rules that expose the NAS
Migrate stored data to a vendor-supported storage platform and power down the legacy device

bash

# Configuration example: block management access to the DNS-320 at an upstream firewall (iptables)
iptables -A FORWARD -p tcp -d <DNS320_IP> --dport 80  -j DROP
iptables -A FORWARD -p tcp -d <DNS320_IP> --dport 443 -j DROP
iptables -A FORWARD -p tcp -s <ADMIN_JUMP_HOST> -d <DNS320_IP> --dport 80  -j ACCEPT
iptables -A FORWARD -p tcp -s <ADMIN_JUMP_HOST> -d <DNS320_IP> --dport 443 -j ACCEPT