CVE-2025-5624: D-Link DIR-816 Buffer Overflow Vulnerability

CVE-2025-5624 Overview

A critical stack-based buffer overflow vulnerability has been discovered in the D-Link DIR-816 router firmware version 1.10CNB05. This vulnerability exists in the QoSPortSetup function within the /goform/QoSPortSetup endpoint, where improper handling of the port0_group, port0_remarker, ssid0_group, and ssid0_remarker arguments allows remote attackers to trigger a buffer overflow condition. As a network-accessible vulnerability requiring no authentication, this flaw poses a significant risk to affected devices.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially execute arbitrary code with elevated privileges on the affected D-Link DIR-816 routers, compromising network security and enabling further attacks on connected devices.

Affected Products

• D-Link DIR-816 Firmware version 1.10CNB05
• D-Link DIR-816 Hardware

Discovery Timeline

• June 5, 2025 - CVE-2025-5624 published to NVD
• June 6, 2025 - Last updated in NVD database

Technical Details for CVE-2025-5624

Vulnerability Analysis

This vulnerability stems from improper memory bounds checking in the QoSPortSetup function, which handles Quality of Service (QoS) configuration requests on D-Link DIR-816 routers. The function processes user-supplied input through multiple parameters without adequate validation, enabling attackers to overflow stack-allocated buffers. The vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer) and CWE-787 (Out-of-bounds Write).

The attack requires no authentication and can be executed remotely over the network. Since D-Link has declared this product end-of-life, no official patches are expected to be released, making this vulnerability particularly dangerous for environments still operating these devices.

Root Cause

The root cause lies in insufficient input validation and boundary checking when processing the port0_group, port0_remarker, ssid0_group, and ssid0_remarker parameters in the QoS port setup handler. The function allocates a fixed-size stack buffer to store these user-controlled values but fails to verify that the input length does not exceed the buffer capacity. This allows attackers to write beyond the allocated memory region, potentially overwriting critical stack data including return addresses and saved registers.

Attack Vector

The attack vector is network-based, targeting the web management interface of the D-Link DIR-816 router. An attacker can craft malicious HTTP POST requests to the /goform/QoSPortSetup endpoint with oversized values in the vulnerable parameters. Since no authentication is required and the attack complexity is low, any attacker with network access to the device's management interface can exploit this vulnerability.

The exploitation process involves sending specially crafted input that exceeds the expected buffer size, allowing the attacker to overwrite adjacent stack memory. This can lead to control flow hijacking and arbitrary code execution. Technical details and proof-of-concept information have been documented in the GitHub Vulnerability Documentation.

Detection Methods for CVE-2025-5624

Indicators of Compromise

• Unusual HTTP POST requests to /goform/QoSPortSetup with abnormally large parameter values
• Router crashes or unexpected reboots that may indicate exploitation attempts
• Unauthorized configuration changes to QoS settings on affected devices
• Anomalous outbound network traffic from the router suggesting command-and-control communication

Detection Strategies

• Monitor web server logs for HTTP requests to /goform/QoSPortSetup containing unusually long parameter strings
• Implement intrusion detection signatures to flag oversized QoS configuration requests
• Deploy network-level monitoring to detect exploitation attempts against D-Link router management interfaces
• Enable logging on network firewalls to capture traffic destined for router management ports

Monitoring Recommendations

• Configure alerts for any access attempts to the router's web management interface from untrusted networks
• Implement network segmentation to isolate management interfaces from general network traffic
• Deploy SentinelOne Singularity to monitor network endpoints for lateral movement following potential router compromise
• Regularly review router access logs for suspicious authentication attempts or configuration changes

How to Mitigate CVE-2025-5624

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Implement firewall rules to block external access to ports 80 and 443 on affected devices
• Consider replacing end-of-life D-Link DIR-816 routers with supported models that receive security updates
• Disable remote management features if not explicitly required

Patch Information

No official patch is available. D-Link has classified the DIR-816 as end-of-life, meaning this product is no longer supported by the maintainer and will not receive security updates. Organizations using affected devices should prioritize replacement with currently supported router models.

Additional information about this vulnerability can be found at VulDB #311110 and the D-Link Official Website.

Workarounds

• Deploy a web application firewall (WAF) in front of the router management interface to filter malicious requests
• Implement strict network access controls limiting management interface access to specific IP addresses
• Use a VPN for any required remote administration rather than exposing the management interface directly
• Monitor the device for signs of compromise and prepare incident response procedures

# Example firewall rules to restrict management access (iptables)
# Block external access to router management interface
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP

# Allow management only from specific trusted admin workstation
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.100 -j ACCEPT