CVE-2026-5980: D-Link DIR-605L Buffer Overflow Flaw

CVE-2026-5980 Overview

A buffer overflow vulnerability has been identified in the D-Link DIR-605L router firmware version 2.13B01. This security flaw affects the formSetMACFilter function within the /goform/formSetMACFilter endpoint of the POST Request Handler component. Attackers can exploit this vulnerability by manipulating the curTime argument to trigger a buffer overflow condition, potentially leading to remote code execution or system compromise.

Critical Impact

This vulnerability allows remote attackers to exploit a buffer overflow in the MAC filter configuration handler, potentially gaining control of affected D-Link routers. The affected product is end-of-life and no longer supported by the vendor.

Affected Products

• D-Link DIR-605L firmware version 2.13B01
• D-Link DIR-605L routers (End-of-Life product)

Discovery Timeline

• April 9, 2026 - CVE-2026-5980 published to NVD
• April 9, 2026 - Last updated in NVD database

Technical Details for CVE-2026-5980

Vulnerability Analysis

This buffer overflow vulnerability (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer) exists in the formSetMACFilter function responsible for processing MAC address filtering configuration requests. The function fails to properly validate the length of the curTime parameter before copying it into a fixed-size buffer, allowing an attacker to overflow the buffer boundaries and potentially overwrite adjacent memory.

The vulnerability is particularly concerning because it can be exploited remotely over the network without requiring physical access to the device. An authenticated attacker with low privileges can send specially crafted POST requests to the /goform/formSetMACFilter endpoint, causing the buffer overflow condition. Successful exploitation could allow attackers to execute arbitrary code, crash the device, or gain elevated privileges on the router.

This vulnerability affects a product that has reached end-of-life status and is no longer receiving security updates from D-Link, leaving users with no official patch available.

Root Cause

The root cause of this vulnerability is improper bounds checking in the formSetMACFilter function when handling the curTime parameter from incoming POST requests. The function allocates a fixed-size buffer to store the parameter value but does not validate that the input length does not exceed the buffer capacity. This classic buffer overflow pattern allows attackers to write beyond allocated memory boundaries when supplying an oversized curTime value.

Attack Vector

The attack vector for CVE-2026-5980 is network-based, requiring the attacker to have network access to the vulnerable router's web management interface. The exploitation process involves:

1. Identifying a D-Link DIR-605L router running vulnerable firmware version 2.13B01
2. Authenticating to the router's web interface (low privilege level required)
3. Sending a malicious POST request to /goform/formSetMACFilter with an oversized curTime parameter
4. The buffer overflow overwrites critical memory structures, potentially allowing code execution

The vulnerability has been publicly disclosed with exploit details available, increasing the risk of active exploitation in the wild.

Detection Methods for CVE-2026-5980

Indicators of Compromise

• Unusual POST requests to /goform/formSetMACFilter with abnormally long curTime parameter values
• Unexpected router crashes or reboots indicating potential exploitation attempts
• Anomalous network traffic patterns targeting router management interfaces
• Modified router configurations or unauthorized access to administrative functions

Detection Strategies

• Monitor web server logs for POST requests to /goform/formSetMACFilter containing excessively long parameter values
• Implement network intrusion detection rules to identify buffer overflow exploit patterns targeting D-Link routers
• Deploy SentinelOne Singularity to detect anomalous behavior patterns associated with router compromise
• Conduct regular firmware version audits to identify vulnerable D-Link DIR-605L devices on the network

Monitoring Recommendations

• Enable logging on network boundary devices to capture traffic to/from D-Link router management interfaces
• Configure alerts for repeated authentication attempts or unusual administrative access patterns
• Monitor for DNS or routing changes that could indicate router compromise
• Regularly review device inventories to identify end-of-life equipment requiring replacement

How to Mitigate CVE-2026-5980

Immediate Actions Required

• Replace affected D-Link DIR-605L routers with currently supported models that receive security updates
• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote management features if not required
• Implement network segmentation to limit potential lateral movement if a router is compromised
• Block external access to port 80/443 on vulnerable routers at the network perimeter

Patch Information

D-Link has classified the DIR-605L as an end-of-life product that no longer receives security updates. No official patch is available for this vulnerability. D-Link recommends retiring affected devices and replacing them with current-generation routers. For additional information, refer to the D-Link Official Website and the Notion Vulnerability Report for technical details.

Workarounds

• Disable the web management interface entirely if feasible for your environment
• Implement strict firewall rules to limit access to the router's management interface to specific trusted IP addresses
• Place vulnerable routers behind a separate firewall with strict access controls
• Consider using a VPN for any necessary remote administration rather than exposing the management interface

# Example firewall rule to restrict access to router management (adjust IPs as needed)
# 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