CVE-2026-2856: D-Link DWR-M960 Buffer Overflow Flaw

CVE-2026-2856 Overview

A stack-based buffer overflow vulnerability has been identified in D-Link DWR-M960 router firmware version 1.01.07. This vulnerability exists within the sub_424AFC function located in the /boafrm/formFilter Filter Configuration Endpoint. Improper handling of the submit-url argument allows a remote attacker to trigger a buffer overflow condition, potentially leading to arbitrary code execution or denial of service on the affected device.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to compromise 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
• D-Link DWR-M960 4G LTE Router

Discovery Timeline

• 2026-02-20 - CVE-2026-2856 published to NVD
• 2026-02-23 - Last updated in NVD database

Technical Details for CVE-2026-2856

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The vulnerable function sub_424AFC fails to properly validate the length of user-supplied input passed through the submit-url parameter before copying it to a stack-allocated buffer. When an attacker submits an oversized value for this parameter, the function writes beyond the allocated buffer boundary, corrupting adjacent stack memory including potentially the return address.

The attack can be launched remotely over the network and requires only low privileges, making it accessible to authenticated users of the router's web interface. The exploit has been publicly disclosed, increasing the risk of active exploitation in the wild.

Root Cause

The root cause of this vulnerability is insufficient bounds checking in the sub_424AFC function when processing the submit-url parameter within the Filter Configuration Endpoint. The function allocates a fixed-size buffer on the stack and uses an unsafe copy operation that does not verify input length against buffer capacity. This classic memory safety issue allows stack memory corruption when processing maliciously crafted HTTP requests.

Attack Vector

The attack vector is network-based, targeting the /boafrm/formFilter endpoint on the router's web management interface. An attacker with low-level authentication can craft a malicious HTTP request containing an oversized submit-url parameter value. When the vulnerable function processes this request, the overflow occurs, potentially allowing the attacker to:

1. Overwrite the saved return address to redirect execution flow
2. Inject shellcode into the stack buffer for code execution
3. Cause a denial of service by crashing the router's web service

The vulnerability is particularly concerning for IoT/embedded devices like routers, which often have limited security protections such as ASLR or stack canaries.

Detection Methods for CVE-2026-2856

Indicators of Compromise

• Unusual HTTP POST requests to /boafrm/formFilter containing excessively long submit-url parameter values
• Router crashes or unexpected reboots coinciding with web management interface access
• Abnormal memory consumption or error logs related to the BOA web server component
• Unexpected outbound network connections from the router indicating potential compromise

Detection Strategies

• Monitor HTTP request logs for requests to /boafrm/formFilter with submit-url parameters exceeding normal length thresholds (e.g., >1024 bytes)
• Implement network-based intrusion detection rules to flag suspicious traffic patterns to D-Link router management interfaces
• Enable logging on the router and review for segmentation faults, stack smashing detected messages, or unexpected service restarts
• Deploy SentinelOne Singularity for network-connected endpoints to detect post-exploitation lateral movement

Monitoring Recommendations

• Establish baseline traffic patterns for router management interface access and alert on anomalies
• Configure SIEM rules to correlate router reboot events with preceding web interface access logs
• Implement network segmentation to isolate router management interfaces from untrusted network segments

How to Mitigate CVE-2026-2856

Immediate Actions Required

• Check the D-Link Security Resource for firmware updates addressing this vulnerability
• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management access if not required for operations
• Place the router behind a firewall with strict ingress filtering
• Monitor the router for signs of compromise and prepare for device replacement if no patch is available

Patch Information

As of the last update on 2026-02-23, no official patch information has been released by D-Link. Organizations should monitor the D-Link Security Resource for security advisories and firmware updates. Additional technical details and community discussion can be found in the GitHub Issue Discussion and the VulDB entry.

Workarounds

• Disable the web management interface entirely and use alternative management methods (SSH/console) if available
• Implement network ACLs to restrict access to the /boafrm/formFilter endpoint
• Deploy a web application firewall (WAF) in front of the router management interface to filter malicious requests
• Consider replacing vulnerable devices with supported alternatives if D-Link does not provide timely patches

# Example: Restrict management interface access via iptables on upstream firewall
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -s <trusted_admin_ip> -j ACCEPT
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -s <trusted_admin_ip> -j ACCEPT
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP