CVE-2025-5630: D-Link DIR-816 Buffer Overflow Vulnerability

CVE-2025-5630 Overview

A critical stack-based buffer overflow vulnerability has been discovered in the D-Link DIR-816 router firmware version 1.10CNB05. This vulnerability affects the /goform/form2lansetup.cgi file, where improper handling of the ip argument allows an attacker to trigger a stack-based buffer overflow condition. The vulnerability can be exploited remotely without authentication, potentially enabling complete device compromise.

Critical Impact

This vulnerability enables remote attackers to execute arbitrary code on affected D-Link DIR-816 routers through a network-based attack requiring no user interaction or authentication. The affected product has reached end-of-life status and is no longer supported by D-Link.

Affected Products

• D-Link DIR-816 Firmware version 1.10CNB05
• D-Link DIR-816 Hardware (all variants running affected firmware)

Discovery Timeline

• June 5, 2025 - CVE-2025-5630 published to NVD
• June 6, 2025 - Last updated in NVD database

Technical Details for CVE-2025-5630

Vulnerability Analysis

This vulnerability is classified under CWE-787 (Out-of-bounds Write) and CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw exists in the LAN setup configuration handler, specifically within the /goform/form2lansetup.cgi endpoint. When processing the ip parameter, the firmware fails to properly validate the length of user-supplied input before copying it to a fixed-size stack buffer, resulting in a classic stack-based buffer overflow condition.

The vulnerability is particularly severe because the affected endpoint is accessible without authentication over the network. An attacker can craft malicious HTTP requests containing oversized ip parameter values that exceed the allocated buffer size, allowing them to overwrite adjacent stack memory including saved return addresses. This can lead to arbitrary code execution with the privileges of the web server process, typically running as root on embedded devices.

Root Cause

The root cause of this vulnerability is the absence of proper bounds checking when handling the ip argument in the LAN setup CGI handler. The firmware uses unsafe string handling functions that do not verify the length of input data against the destination buffer capacity. When user-controlled data is copied to a stack-allocated buffer without length validation, an attacker can supply input that exceeds the buffer boundaries, corrupting adjacent memory on the stack.

Attack Vector

The attack vector is network-based, allowing remote exploitation without requiring authentication or user interaction. An attacker with network access to the router's management interface can send specially crafted HTTP POST requests to the /goform/form2lansetup.cgi endpoint with a malicious ip parameter value.

The attack sequence involves:

1. Identifying a vulnerable D-Link DIR-816 router on the network
2. Crafting an HTTP request to the vulnerable CGI endpoint
3. Including an oversized ip parameter value designed to overflow the stack buffer
4. Overwriting the return address to redirect execution flow
5. Gaining arbitrary code execution on the device

The exploit has been publicly disclosed and documented in the GitHub Vulnerability Documentation, increasing the risk of active exploitation in the wild.

Detection Methods for CVE-2025-5630

Indicators of Compromise

• Unusual HTTP POST requests to /goform/form2lansetup.cgi with abnormally long ip parameter values
• Unexpected router reboots or crashes following network traffic to the management interface
• Modified router configurations or firmware without administrator action
• Suspicious outbound network connections originating from the router

Detection Strategies

• Monitor HTTP traffic to D-Link router management interfaces for requests containing oversized parameters in CGI form submissions
• Implement intrusion detection rules to flag POST requests to /goform/form2lansetup.cgi with ip parameter values exceeding typical IPv4 address lengths (15 characters)
• Deploy network anomaly detection to identify potential buffer overflow attempts targeting embedded device web interfaces

Monitoring Recommendations

• Implement network segmentation to isolate IoT and router management interfaces from untrusted networks
• Enable logging on network firewalls to capture traffic destined for router management ports
• Regularly review router access logs for signs of exploitation attempts or unauthorized configuration changes

How to Mitigate CVE-2025-5630

Immediate Actions Required

• Immediately restrict network access to the router's management interface to trusted administrative hosts only
• Disable remote management features if not required for operations
• Consider replacing the affected D-Link DIR-816 router with a currently supported device, as this product has reached end-of-life

Patch Information

This vulnerability affects a D-Link product that is no longer supported by the maintainer. D-Link has not released and is not expected to release a security patch for this vulnerability. Organizations using affected devices should prioritize hardware replacement with currently supported router models. For additional information, visit the D-Link Official Website.

Additional technical details are available from VulDB #311116.

Workarounds

• Implement firewall rules to block external access to the router's web management interface (typically port 80/443)
• Use access control lists (ACLs) to restrict management interface access to specific trusted IP addresses
• Disable the web management interface entirely if alternative management methods are available
• Place the router behind a network firewall that can inspect and filter malicious HTTP requests

# Example iptables rules to restrict management interface access
# Apply on upstream firewall or gateway device
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -j DROP
# Allow management only from trusted admin workstation
iptables -I FORWARD -s <ADMIN_IP> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT