CVE-2025-0492: D-Link DIR-823X Firmware DOS Vulnerability

CVE-2025-0492 Overview

A critical null pointer dereference vulnerability has been discovered in D-Link DIR-823X routers running firmware versions 240126 and 240802. The vulnerability affects the function FUN_00412244 and can be exploited remotely without authentication, potentially causing a denial of service condition. The exploit details have been publicly disclosed, increasing the risk of exploitation in the wild.

Critical Impact

Remote attackers can exploit this vulnerability to cause a denial of service on affected D-Link DIR-823X routers, potentially disrupting network connectivity for all connected devices.

Affected Products

• D-Link DIR-823X Firmware version 240126
• D-Link DIR-823X Firmware version 240802
• D-Link DIR-823X Hardware (all revisions with affected firmware)

Discovery Timeline

• 2025-01-15 - CVE-2025-0492 published to NVD
• 2025-09-24 - Last updated in NVD database

Technical Details for CVE-2025-0492

Vulnerability Analysis

This vulnerability is classified as a null pointer dereference (CWE-404) within the D-Link DIR-823X router firmware. The flaw resides in the function FUN_00412244, where improper handling of certain inputs allows an attacker to trigger a condition that dereferences a null pointer. When successfully exploited, this causes the router's firmware to crash, resulting in a denial of service condition.

The network-accessible nature of this vulnerability is particularly concerning for consumer and small business environments where D-Link DIR-823X routers are commonly deployed. No authentication is required to trigger the vulnerability, and the attack can be executed remotely over the network.

Root Cause

The root cause of CVE-2025-0492 lies in improper resource management within the FUN_00412244 function. The firmware fails to properly validate or initialize pointer references before use, creating a condition where a null pointer can be dereferenced. This is a common programming error in embedded device firmware where memory safety checks are not consistently implemented.

The CWE-404 classification indicates improper resource shutdown or release, suggesting that the vulnerability may be triggered during resource cleanup or deallocation operations where pointer state is not properly verified.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no user interaction or authentication. An attacker with network access to the router's management interface can craft malicious requests that trigger the null pointer dereference condition in FUN_00412244.

The vulnerability mechanism involves sending specially crafted input to the affected function, which fails to handle edge cases properly. When the function attempts to access memory through the unvalidated pointer, the system crashes due to the null dereference.

Detailed technical analysis of the exploitation method is available in the Notion Security Advisory.

Detection Methods for CVE-2025-0492

Indicators of Compromise

• Unexpected router reboots or service interruptions without apparent cause
• Repeated crash logs referencing the FUN_00412244 function in router diagnostics
• Unusual network traffic patterns targeting the router's management ports
• Multiple failed connection attempts to the router's web interface from external sources

Detection Strategies

• Monitor network traffic for anomalous requests to D-Link DIR-823X management interfaces
• Implement intrusion detection rules to identify patterns associated with null pointer exploitation attempts
• Review router system logs for crash events or unexpected service restarts
• Deploy network-based anomaly detection to identify reconnaissance and exploitation attempts targeting router firmware

Monitoring Recommendations

• Enable logging on D-Link router management interfaces and forward logs to a centralized SIEM
• Configure alerts for router availability monitoring to detect denial of service conditions
• Implement network segmentation to limit external access to router management interfaces
• Regularly review access control lists for management interface exposure

How to Mitigate CVE-2025-0492

Immediate Actions Required

• Restrict network access to the router's management interface to trusted internal networks only
• Disable remote management features if not required for operations
• Monitor for firmware updates from D-Link and apply patches as soon as available
• Consider replacing affected devices with supported alternatives if patches are not available

Patch Information

At the time of this writing, no official patch has been confirmed from D-Link for this vulnerability. Users should monitor the D-Link Official Website for firmware updates addressing CVE-2025-0492. Given D-Link's history with end-of-life devices, affected users should verify whether their DIR-823X model is still receiving security updates.

Additional vulnerability details can be found at VulDB #291937.

Workarounds

• Disable remote management access to prevent external exploitation
• Implement firewall rules to block external access to management ports (typically ports 80, 443, and 8080)
• Use network segmentation to isolate the router management interface from untrusted networks
• Consider deploying a firewall or security appliance in front of the affected router to filter malicious traffic

# Example iptables rules to restrict management access (apply on upstream firewall)
# Block external access to common D-Link management ports
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.0.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.0.0/24 -j DROP
iptables -A INPUT -p tcp --dport 8080 -s ! 192.168.0.0/24 -j DROP