CVE-2025-7553: D-Link DIR-818LW Firmware RCE Vulnerability

CVE-2025-7553 Overview

CVE-2025-7553 is an operating system command injection vulnerability in the D-Link DIR-818LW wireless router, affecting firmware versions up to 20191215. The flaw resides in the System Time Page component, where the NTP Server argument is passed to a system shell without proper sanitization. An authenticated remote attacker can inject arbitrary OS commands through this parameter. The vulnerability has been publicly disclosed and affects a product line that D-Link no longer supports. Because the device has reached end-of-life, no official patch will be released.

Critical Impact
Authenticated attackers can execute arbitrary operating system commands on the router, enabling persistent compromise of the network perimeter device.

Affected Products

D-Link DIR-818LW router (hardware)
D-Link DIR-818LW firmware versions up to and including 20191215
End-of-life devices no longer receiving vendor security updates

Discovery Timeline

2025-07-14 - CVE-2025-7553 published to NVD
2026-04-29 - Last updated in NVD database

Technical Details for CVE-2025-7553

Vulnerability Analysis

The vulnerability is classified under [CWE-77] Command Injection and [CWE-78] OS Command Injection. The DIR-818LW web management interface includes a System Time configuration page that allows administrators to specify a Network Time Protocol (NTP) server. The input supplied for the NTP Server parameter is concatenated into a shell command on the router without proper input validation or sanitization. An attacker who supplies shell metacharacters such as semicolons, backticks, or pipe operators causes the underlying command interpreter to execute attacker-controlled commands alongside the intended NTP query. The exploit requires high privileges, meaning the attacker must possess valid administrative credentials on the device. Successful exploitation grants command execution in the context of the router's web service, typically running as root on embedded Linux-based D-Link firmware.

Root Cause

The root cause is the use of unsanitized user input in a shell command construction within the System Time handler. The firmware passes the NTP Server field directly to a system call that invokes the NTP client, without escaping shell metacharacters or using a safe execution API such as execve with argument arrays.

Attack Vector

The attack vector is network-based and requires authenticated access to the router's administrative web interface. An attacker submits a crafted value for the NTP Server field on the System Time configuration page. The injected payload uses shell separators to break out of the intended command context and execute arbitrary commands. The vulnerability cannot be exploited without valid credentials, which limits unauthenticated mass exploitation but does not prevent attacks following credential theft, default-credential abuse, or insider activity.

No verified proof-of-concept code is published in the referenced advisories. Technical details are tracked in VulDB entry #316251.

Detection Methods for CVE-2025-7553

Indicators of Compromise

Unexpected outbound connections from the router's WAN interface to unknown hosts following NTP configuration changes
Configuration entries in the System Time page containing shell metacharacters such as ;, |, `, $(), or &&
New or unexpected processes spawned by the router web service or NTP client
Modifications to router startup scripts, DNS settings, or firewall rules without administrator action

Detection Strategies

Audit router configuration backups for NTP Server values that contain non-hostname characters
Monitor administrative logins to the DIR-818LW web interface and correlate with configuration changes on the System Time page
Inspect network telemetry for traffic patterns originating from the router that do not match normal NTP, DNS, or management flows

Monitoring Recommendations

Forward router syslog output to a centralized logging platform and alert on authentication events and configuration changes
Apply network segmentation to restrict administrative access to the router's management interface from trusted hosts only
Track outbound connections from the router itself, which should normally be limited to NTP, DNS, and firmware update endpoints

How to Mitigate CVE-2025-7553

Immediate Actions Required

Replace the DIR-818LW with a currently supported router model, as the device is end-of-life and will not receive a patch
Change the administrative password to a strong, unique value and disable any default accounts
Disable remote (WAN-side) administration on the router to limit the attack surface to the local network
Restrict access to the management interface to a dedicated management VLAN or specific trusted IP addresses

Patch Information

No patch is available. D-Link has confirmed that the DIR-818LW is no longer supported and will not receive security updates. Refer to D-Link Security Information for the official end-of-life statement. The only durable remediation is hardware replacement with a supported device.

Workarounds

Isolate the DIR-818LW behind an upstream firewall that filters inbound management traffic
Disable the System Time configuration page through access control rules if the firmware allows it, and rely on default NTP settings
Limit administrative credentials to a small number of trusted operators and rotate them frequently until replacement
Monitor the router with external network sensors since the device itself cannot be assumed to produce reliable logs after compromise

bash

# Example: restrict router management interface to a single admin host using an upstream firewall (iptables)
iptables -A FORWARD -s 192.0.2.10 -d 192.168.0.1 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d 192.168.0.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.0.1 -p tcp --dport 443 -j DROP