CVE-2025-5624: D-Link DIR-816 Buffer Overflow Flaw

CVE-2025-5624 Overview

CVE-2025-5624 is a stack-based buffer overflow vulnerability in the D-Link DIR-816 router running firmware version 1.10CNB05. The flaw resides in the QoSPortSetup function exposed through the /goform/QoSPortSetup endpoint. Attackers can trigger the overflow by manipulating the port0_group, port0_remarker, ssid0_group, or ssid0_remarker arguments. The vulnerability is reachable remotely without authentication and the exploit details have been publicly disclosed. D-Link no longer supports the DIR-816 product line, meaning no official patch will be issued. The vulnerability maps to [CWE-119] (improper restriction of operations within memory buffer bounds) and [CWE-787] (out-of-bounds write).

Critical Impact
Unauthenticated remote attackers can corrupt stack memory on affected DIR-816 routers, leading to denial of service or arbitrary code execution on an end-of-life device that will not receive a vendor fix.

Affected Products

D-Link DIR-816 hardware router (end-of-life)
D-Link DIR-816 firmware version 1.10CNB05
Any deployment exposing /goform/QoSPortSetup to untrusted networks

Discovery Timeline

2025-06-05 - CVE-2025-5624 published to NVD
2025-06-06 - Last updated in NVD database

Technical Details for CVE-2025-5624

Vulnerability Analysis

The vulnerability exists in the QoSPortSetup handler reachable through the web management interface at /goform/QoSPortSetup. The handler accepts user-controlled HTTP parameters and copies them into fixed-size stack buffers without enforcing length checks. Supplying oversized values for port0_group, port0_remarker, ssid0_group, or ssid0_remarker overwrites adjacent stack memory, including saved return addresses and frame pointers. An attacker who controls the overwritten data can redirect execution flow within the embedded HTTP daemon. The router does not implement modern exploit mitigations consistently across its MIPS-based binaries, increasing the reliability of code execution. Because authentication is not required prior to reaching the vulnerable parser path, the attack surface includes any network position with access to the device administration interface.

Root Cause

The root cause is missing bounds validation when the QoSPortSetup function copies request parameters into stack-allocated buffers. Functions in the C standard library that do not enforce destination size limits, such as strcpy or sprintf, are typical sources of this class of defect in embedded D-Link firmware.

Attack Vector

An attacker sends a crafted HTTP POST request to /goform/QoSPortSetup containing oversized values in one or more of the vulnerable QoS parameters. No credentials, user interaction, or prior foothold are required. Successful exploitation can crash the management daemon or hijack control flow to execute attacker-supplied shellcode on the router.

No verified proof-of-concept code is included here. Technical details on the parameter handling and overflow path are documented in the GitHub Vulnerability Report and the VulDB entry.

Detection Methods for CVE-2025-5624

Indicators of Compromise

HTTP POST requests to /goform/QoSPortSetup containing parameter values exceeding typical lengths (hundreds of bytes) for port0_group, port0_remarker, ssid0_group, or ssid0_remarker.
Repeated crashes, reboots, or unavailability of the DIR-816 web administration interface.
Outbound connections from the router to unfamiliar hosts, including TFTP, HTTP, or IRC traffic typical of router botnet payloads.
Unexpected configuration changes to QoS, DNS, or firewall rules following requests to /goform/QoSPortSetup.

Detection Strategies

Inspect HTTP traffic destined for the router management interface and alert on request bodies targeting /goform/QoSPortSetup with non-printable or oversized parameter values.
Apply network signatures that match the parameter names listed above when accompanied by payloads longer than the firmware's expected input size.
Correlate router crash telemetry or syslog reboot events with preceding HTTP requests to the QoS endpoint.

Monitoring Recommendations

Forward router syslog and SNMP trap data to a centralized logging platform and alert on management daemon restarts.
Monitor LAN segments for unauthorized hosts attempting to reach router administration interfaces.
Track DNS resolution patterns from the router itself to identify compromise-driven traffic redirection.

How to Mitigate CVE-2025-5624

Immediate Actions Required

Replace affected D-Link DIR-816 devices with a currently supported router model, as the product is end-of-life and no patch will be released.
Remove the management interface from any WAN-facing exposure and confirm remote administration is disabled.
Restrict LAN access to the web interface to a dedicated management VLAN or specific administrator hosts.
Rotate administrator credentials and audit current QoS, DNS, and port-forwarding configuration for tampering.

Patch Information

D-Link has confirmed that the DIR-816 is no longer supported. No official firmware update is planned. Refer to the D-Link Official Website for end-of-life notices and replacement model guidance.

Workarounds

Block inbound traffic to /goform/QoSPortSetup at an upstream firewall or reverse proxy if the device must remain in service temporarily.
Disable remote management and limit administrative access to wired LAN clients only.
Segment the affected router on an isolated network so a compromise cannot pivot into sensitive infrastructure.
Plan and execute hardware replacement on a defined timeline to eliminate exposure permanently.

bash

# Example upstream firewall rule to block external access to the vulnerable endpoint
# (adjust interface and router IP to match the environment)
iptables -I FORWARD -p tcp -d 192.0.2.10 --dport 80 \
  -m string --string "/goform/QoSPortSetup" --algo bm -j DROP