CVE-2025-2551: D-Link DIR-618 Authentication Bypass Flaw

CVE-2025-2551 Overview

CVE-2025-2551 is an improper access control vulnerability [CWE-266] affecting D-Link DIR-618 and DIR-605L routers running firmware versions 2.02 and 3.02 respectively. The flaw resides in the /goform/formSetPortTr endpoint. An attacker with access to the local network can manipulate the endpoint to bypass access controls and modify port trigger configurations. The exploit details have been publicly disclosed. Both affected devices are end-of-life and no longer receive security updates from D-Link.

Critical Impact
An adjacent-network attacker can abuse /goform/formSetPortTr to alter router configuration without proper authorization, and no vendor patch is available because the affected devices are end-of-life.

Affected Products

D-Link DIR-618 firmware version 2.02
D-Link DIR-605L firmware version 3.02
Both models are no longer supported by the vendor

Discovery Timeline

2025-03-20 - CVE-2025-2551 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-2551

Vulnerability Analysis

The vulnerability affects the formSetPortTr handler exposed under the router's /goform/ HTTP interface. This endpoint controls port triggering configuration on the device. The handler fails to enforce proper access controls before processing incoming requests. An attacker on the same local network segment can send crafted HTTP requests to modify port trigger rules without holding the required privileges.

The flaw is classified under CWE-266 (Incorrect Privilege Assignment), indicating that the endpoint grants operational access beyond what its role should permit. Because these devices sit at the network edge, unauthorized modification of port triggers can expose internal services or redirect traffic in unintended ways.

Root Cause

The root cause is missing or insufficient authorization checks in the formSetPortTr request handler. The web management interface accepts configuration changes on this endpoint without verifying that the requester holds administrative privileges. This design flaw is common in legacy small office and home office (SOHO) router firmware where administrative endpoints rely on session context that is not consistently enforced.

Attack Vector

Exploitation requires adjacent network access, meaning the attacker must be on the same local network as the target router. This can be achieved through a compromised device on the LAN, a rogue wireless client, or a hostile insider. Once connected, the attacker issues HTTP requests directly to /goform/formSetPortTr to alter port triggering rules. No prior authentication and no user interaction are required. Refer to the VulDB entry #300165 and the technical write-ups for DIR-605L and DIR-618 for endpoint-level analysis.

Detection Methods for CVE-2025-2551

Indicators of Compromise

Unexpected HTTP POST requests to /goform/formSetPortTr originating from LAN clients
Unauthorized changes to port triggering rules in the router configuration
New or modified port forwarding entries that do not match administrator activity
Presence of end-of-life D-Link DIR-618 or DIR-605L devices in the network inventory

Detection Strategies

Monitor internal HTTP traffic destined for router management interfaces on the LAN
Alert on requests to /goform/ endpoints from non-administrator endpoints
Baseline router configuration and detect deviations in port triggering or forwarding tables
Correlate device inventory data to identify unsupported D-Link models still in use

Monitoring Recommendations

Enable logging on network segmentation devices to capture LAN-side HTTP flows to the router
Periodically export router configuration and diff against a trusted baseline
Watch for lateral movement behaviors originating from LAN hosts targeting gateway IPs
Track SOHO firmware versions using asset management to flag out-of-support devices

How to Mitigate CVE-2025-2551

Immediate Actions Required

Replace affected DIR-618 and DIR-605L devices with vendor-supported hardware
Restrict access to the router management interface to a dedicated administrative VLAN
Disable remote and untrusted-client access to the web administration interface
Segment untrusted wireless and guest networks away from the router LAN interface

Patch Information

No vendor patch is available. D-Link has designated the DIR-618 and DIR-605L as end-of-life, and the vendor will not release security updates for these models. Refer to the D-Link official website for current supported product lines and replace affected units accordingly.

Workarounds

Block LAN client access to /goform/formSetPortTr using an upstream firewall or network access control policy
Enforce network segmentation so only trusted administrative hosts can reach the router web interface
Disable port triggering functionality if not required by the environment
Migrate to a supported router platform that receives active security maintenance

bash

# Example: restrict router management access to a single admin host via iptables on an upstream gateway
iptables -A FORWARD -s 192.168.1.10 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP