CVE-2026-2961: D-Link DWR-M960 Buffer Overflow Flaw

CVE-2026-2961 Overview

A stack-based buffer overflow vulnerability has been discovered in the D-Link DWR-M960 mobile router firmware version 1.01.07. This firmware vulnerability affects the function sub_4196C4 within the /boafrm/formVpnConfigSetup file, which is part of the VPN Configuration Endpoint component. The vulnerability is triggered through manipulation of the submit-url argument, allowing attackers to overflow stack memory buffers. This security flaw can be exploited remotely over the network, making it particularly dangerous for devices exposed to the internet.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially execute arbitrary code or cause denial of service on affected D-Link DWR-M960 routers, compromising network security and device integrity.

Affected Products

• D-Link DWR-M960 Firmware version 1.01.07
• D-Link DWR-M960 Hardware revision B1
• D-Link DWR-M960 mobile router devices running vulnerable firmware

Discovery Timeline

• February 23, 2026 - CVE-2026-2961 published to NVD
• February 23, 2026 - Last updated in NVD database

Technical Details for CVE-2026-2961

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The vulnerable component resides in the VPN configuration functionality of the D-Link DWR-M960 router's web interface. When processing VPN configuration requests through the /boafrm/formVpnConfigSetup endpoint, the sub_4196C4 function fails to properly validate the length of user-supplied input in the submit-url parameter before copying it to a fixed-size stack buffer.

The attack can be initiated remotely over the network and requires low-level privileges to execute. No user interaction is required for successful exploitation. The potential impact includes complete compromise of device confidentiality, integrity, and availability, though the scope is limited to the vulnerable device itself.

Root Cause

The root cause of this vulnerability is insufficient bounds checking in the sub_4196C4 function when handling the submit-url parameter. The function allocates a fixed-size buffer on the stack and copies user-controlled input without verifying that the input length does not exceed the buffer capacity. This classic buffer overflow pattern allows attackers to overwrite adjacent stack memory, including return addresses and saved registers.

Attack Vector

The attack is network-based and targets the VPN Configuration Endpoint accessible via the router's web management interface. An attacker with network access to the device's administration interface can craft a malicious HTTP request to the /boafrm/formVpnConfigSetup endpoint containing an oversized submit-url parameter value. When processed by the vulnerable function, the excessive data overflows the stack buffer, potentially allowing the attacker to hijack program execution flow.

The vulnerability mechanism involves sending a crafted HTTP POST request to the VPN configuration endpoint with a maliciously long submit-url parameter. The sub_4196C4 function processes this input without adequate length validation, resulting in stack memory corruption. Successful exploitation could lead to arbitrary code execution with the privileges of the web server process, typically running as root on embedded devices. For detailed technical analysis, refer to the GitHub Issue Discussion and VulDB entry #347328.

Detection Methods for CVE-2026-2961

Indicators of Compromise

• Unusual HTTP POST requests to /boafrm/formVpnConfigSetup with abnormally large payloads or long submit-url parameter values
• Router crashes, unexpected reboots, or unresponsive web interface following VPN configuration attempts
• Anomalous outbound network connections from the router device to unknown external IP addresses
• Modified router configurations or unauthorized VPN tunnels appearing in device settings

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests to vulnerable D-Link endpoints with oversized parameters
• Monitor router device logs for segmentation faults, buffer overflow errors, or web server crashes
• Deploy packet inspection to detect malformed requests targeting /boafrm/formVpnConfigSetup with submit-url parameters exceeding normal length thresholds
• Use SentinelOne Singularity platform for network visibility and detection of exploitation attempts against IoT devices

Monitoring Recommendations

• Enable verbose logging on network perimeter devices to capture traffic destined for D-Link router management interfaces
• Establish baseline behavior for router web interface access patterns and alert on deviations
• Configure SIEM alerts for multiple failed or malformed requests to D-Link device endpoints
• Regularly audit router configurations for unauthorized changes that may indicate successful compromise

How to Mitigate CVE-2026-2961

Immediate Actions Required

• Restrict network access to the router's web management interface to trusted IP addresses only
• Disable remote administration if not required and limit access to local network management only
• Implement firewall rules to block external access to ports 80, 443, and any other management ports on affected devices
• Monitor the D-Link Security Resources page for firmware updates addressing this vulnerability
• Consider replacing end-of-life D-Link devices with supported models that receive security updates

Patch Information

As of the last modification date (February 23, 2026), no official patch has been released by D-Link for this vulnerability. Users should monitor the D-Link support portal and security advisories for firmware updates. Check the VulDB entry and the GitHub Issue Discussion for the latest information on available fixes and vendor response.

Workarounds

• Isolate affected D-Link DWR-M960 devices on a separate network segment with strict access controls
• Use a VPN or jump host to access the router management interface instead of exposing it directly
• Implement Web Application Firewall (WAF) rules to filter requests with abnormally long parameters to the affected endpoint
• Disable the VPN configuration feature if not in use until a patch becomes available

# Example iptables rules to restrict management access
# Replace 192.168.1.0/24 with your trusted management subnet

# Block external access to HTTP management interface
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP

# Block external access to HTTPS management interface
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP

# Log blocked attempts for monitoring
iptables -A INPUT -p tcp --dport 80 -j LOG --log-prefix "DLINK-MGMT-BLOCKED: "
iptables -A INPUT -p tcp --dport 443 -j LOG --log-prefix "DLINK-MGMT-BLOCKED: "