CVE-2026-2855: D-Link DWR-M960 Buffer Overflow Vulnerability

CVE-2026-2855 Overview

A stack-based buffer overflow vulnerability has been discovered in the D-Link DWR-M960 mobile router firmware version 1.01.07. The vulnerability affects the function sub_4648F0 within the file /boafrm/formDdns, which is part of the DDNS Settings Handler component. Manipulation of the submit-url argument can trigger a stack-based buffer overflow, allowing remote attackers to potentially execute arbitrary code or cause denial of service conditions on affected devices.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to compromise affected D-Link DWR-M960 routers, potentially gaining full control of the device or disrupting network connectivity for connected users.

Affected Products

• D-Link DWR-M960 Firmware version 1.01.07
• D-Link DWR-M960 Hardware revision B1

Discovery Timeline

• February 20, 2026 - CVE-2026-2855 published to NVD
• February 23, 2026 - Last updated in NVD database

Technical Details for CVE-2026-2855

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), representing a classic stack-based buffer overflow condition in embedded firmware. The flaw resides in the DDNS (Dynamic Domain Name System) configuration handler, a component responsible for managing dynamic DNS settings on the router.

The vulnerable function sub_4648F0 processes user-supplied input from the submit-url parameter without adequate bounds checking. When an attacker submits an excessively long string through this parameter, the function writes beyond the allocated buffer space on the stack, corrupting adjacent memory regions including potentially critical control structures such as saved return addresses or frame pointers.

The network-accessible nature of this vulnerability is particularly concerning for IoT devices like routers, which often sit at network perimeters and may be exposed to the internet. Successful exploitation requires only low-privilege authentication, making this a realistic attack vector for threat actors targeting home and small business networks.

Root Cause

The root cause of this vulnerability is the lack of proper input validation and boundary checking in the sub_4648F0 function when processing the submit-url parameter. The function copies user-supplied data into a fixed-size stack buffer without verifying that the input length does not exceed the buffer's capacity. This allows attackers to overflow the buffer and overwrite adjacent stack memory, potentially redirecting execution flow.

Attack Vector

The attack can be initiated remotely over the network by sending a specially crafted HTTP POST request to the /boafrm/formDdns endpoint. An authenticated attacker with low privileges can manipulate the submit-url parameter to include a payload exceeding the expected buffer size. The overflow occurs during the processing of DDNS configuration settings, and the exploit has been publicly disclosed, increasing the risk of active exploitation.

The attack flow typically involves:

1. Authenticating to the router's web management interface (low-privilege access required)
2. Submitting a malicious request to the DDNS settings handler
3. Providing an oversized submit-url parameter value that triggers the buffer overflow
4. Overwriting stack memory to achieve code execution or crash the device

Detection Methods for CVE-2026-2855

Indicators of Compromise

• Unexpected crashes or reboots of D-Link DWR-M960 devices
• Unusual HTTP POST requests to /boafrm/formDdns with abnormally large submit-url parameters
• Modified DDNS configurations or suspicious DNS resolution behavior
• Anomalous outbound connections from the router to unknown external hosts

Detection Strategies

• Monitor network traffic for HTTP POST requests targeting /boafrm/formDdns with payload sizes exceeding normal thresholds
• Implement web application firewall (WAF) rules to detect and block oversized parameters in DDNS-related requests
• Deploy intrusion detection signatures matching known buffer overflow attack patterns against D-Link router endpoints
• Utilize SentinelOne Singularity to identify anomalous behavior patterns on network segments containing vulnerable devices

Monitoring Recommendations

• Enable logging on the D-Link DWR-M960 to capture authentication attempts and configuration changes
• Implement network segmentation to isolate IoT devices and monitor inter-segment traffic
• Set up alerts for repeated failed authentication attempts followed by successful access to administrative endpoints
• Review device firmware versions regularly and correlate with known vulnerability databases

How to Mitigate CVE-2026-2855

Immediate Actions Required

• Restrict administrative access to the D-Link DWR-M960 web interface to trusted internal networks only
• Disable remote management features if not required for operations
• Implement network access controls to limit which hosts can reach the router's management interface
• Monitor for unusual traffic patterns targeting the DDNS settings handler endpoint

Patch Information

At the time of publication, no official patch has been released by D-Link for this vulnerability. Organizations should check the D-Link Security Resource page regularly for firmware updates. Additional technical details and tracking information are available through the VulDB entry #347094 and the GitHub Issue Discussion.

Workarounds

• Disable the DDNS feature on affected devices if dynamic DNS functionality is not required
• Place the router behind an additional firewall that filters malicious requests to the web management interface
• Implement IP whitelisting to restrict access to the router's administrative functions
• Consider replacing end-of-life or unpatched D-Link devices with supported alternatives

# Example: Restrict management interface access via firewall rules
# Block external access to router management port (typically port 80/443)
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