CVE-2026-5214: D-Link DNR-202L Buffer Overflow Flaw

CVE-2026-5214 Overview

A stack-based buffer overflow vulnerability has been identified in multiple D-Link Network Attached Storage (NAS) devices. The vulnerability exists in the cgi_addgroup_get_group_quota_minsize function within the /cgi-bin/account_mgr.cgi file. Remote attackers can exploit this vulnerability by sending specially crafted requests with a malicious Name argument, potentially leading to arbitrary code execution or system compromise on affected devices.

Critical Impact

Remote attackers with low privileges can exploit this stack-based buffer overflow to achieve complete system compromise, potentially gaining full control over affected D-Link NAS devices and accessing stored data.

Affected Products

• D-Link DNS-120, DNS-315L, DNS-320, DNS-320L, DNS-320LW, DNS-321 (firmware up to 20260205)
• D-Link DNS-323, DNS-325, DNS-326, DNS-327L, DNS-340L, DNS-343, DNS-345 (firmware up to 20260205)
• D-Link DNS-726-4, DNS-1100-4, DNS-1200-05, DNS-1550-04 (firmware up to 20260205)
• D-Link DNR-202L, DNR-322L, DNR-326 (firmware up to 20260205)

Discovery Timeline

• 2026-03-31 - CVE-2026-5214 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-5214

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-787: Out-of-bounds Write) with an underlying memory corruption issue (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The affected function cgi_addgroup_get_group_quota_minsize in the account management CGI script fails to properly validate the length of user-supplied input in the Name parameter before copying it to a fixed-size stack buffer.

When an attacker submits an overly long string in the Name argument, the function writes beyond the allocated buffer boundaries on the stack. This can overwrite critical stack data including saved return addresses and frame pointers, enabling attackers to redirect program execution flow. The vulnerability is remotely exploitable over the network and requires only low-level authentication, making it particularly dangerous for internet-exposed NAS devices.

Root Cause

The root cause of this vulnerability is inadequate input validation and bounds checking in the cgi_addgroup_get_group_quota_minsize function. The code does not verify that the length of the Name parameter falls within acceptable bounds before performing memory copy operations. This allows attackers to supply input that exceeds the allocated stack buffer size, resulting in adjacent memory being overwritten. The use of unsafe string handling functions without proper length restrictions enables this classic stack buffer overflow condition.

Attack Vector

The attack is performed remotely over the network by sending a malicious HTTP request to the /cgi-bin/account_mgr.cgi endpoint on vulnerable D-Link NAS devices. The attacker crafts a request containing an excessively long Name parameter value designed to overflow the stack buffer. This overflow can corrupt stack memory, overwrite return addresses, and potentially allow the attacker to inject and execute arbitrary shellcode with the privileges of the web server process running on the NAS device.

The exploitation path involves sending an HTTP POST or GET request to the affected CGI script with the malformed Name parameter. Technical details and proof-of-concept information have been documented in the GitHub vulnerability documentation. Additional information is available through the VulDB entry.

Detection Methods for CVE-2026-5214

Indicators of Compromise

• Unusual HTTP requests to /cgi-bin/account_mgr.cgi containing excessively long Name parameter values
• Web server crashes or unexpected restarts on D-Link NAS devices
• Unexpected processes spawning from the web server process on the NAS device
• Network connections from the NAS device to unknown external IP addresses

Detection Strategies

• Monitor HTTP traffic to D-Link NAS devices for requests containing abnormally long parameter values in CGI requests
• Deploy network intrusion detection rules to identify buffer overflow attack patterns targeting the account_mgr.cgi endpoint
• Implement web application firewall rules to block requests with oversized input parameters
• Review NAS device logs for signs of exploitation attempts or unexpected service behavior

Monitoring Recommendations

• Enable comprehensive logging on D-Link NAS devices and forward logs to a centralized SIEM solution
• Configure network segmentation to isolate NAS devices from direct internet exposure
• Set up alerting for unusual network traffic patterns originating from or destined to NAS devices
• Regularly audit device firmware versions against known vulnerable versions

How to Mitigate CVE-2026-5214

Immediate Actions Required

• Restrict network access to D-Link NAS management interfaces to trusted IP addresses only
• Place affected devices behind a properly configured firewall that blocks external access to CGI endpoints
• Disable remote management features if not required
• Monitor devices for signs of compromise and isolate any potentially compromised systems

Patch Information

At the time of publication, vendor patch status should be verified through the D-Link official website. Many of the affected models are legacy devices that may have reached end-of-life status. Organizations should check D-Link's security advisories for firmware updates addressing this vulnerability. If patches are unavailable for end-of-life products, consider replacing affected devices with supported alternatives.

Workarounds

• Implement network access control lists (ACLs) to restrict access to the /cgi-bin/account_mgr.cgi endpoint
• Deploy a reverse proxy or web application firewall with input validation rules in front of the NAS device
• Disable the web management interface if feasible and manage devices through alternative methods
• Consider network segmentation to place vulnerable NAS devices in isolated network zones with limited connectivity

# Network firewall rule example (iptables)
# Block external access to NAS CGI endpoints
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