D-Link DIR-605 Router Information Disclosure and Credential Theft Vulnerability (CVE-2021-40655) Analysis & Mitigation Guide
Executive & SecOps Summary
SECOPS ASSESSMENTD-Link DIR-605 B2 Firmware Version 2.01MT and prior
Unauthenticated remote attackers can retrieve plaintext administrator credentials by sending a forged POST request to the /getcfg.php page
Immediately decommission and replace the legacy EOL device, or disable remote WAN management and restrict network access
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Since the D-Link DIR-605 is an End-of-Life (EOL) device, official security patches are no longer provided. The recommended action is to replace the hardware with a supported model. If replacement is not immediately possible, restrict all external access.
2. Temporary Workaround & Hardening Configuration
Disable the 'Remote Management' feature in the router's administration panel. If an upstream firewall is present, block all inbound HTTP/HTTPS traffic to the router's management IP using the following rules:
# Block external WAN access to the router's web interface (e.g., 192.168.1.1)
iptables -A INPUT -p tcp -d 192.168.1.1 --dport 80 -j DROP
iptables -A INPUT -p tcp -d 192.168.1.1 --dport 443 -j DROP3. Log Audit & IoC Verification Commands
Audit network traffic and web server logs for unauthorized POST requests to /getcfg.php. You can test if your device is exposed using the following curl command:
# Test if the target router leaks credentials via the vulnerable endpoint
curl -s -d 'services=DEVICE.ACCOUNT' 'http://[TARGET_IP]/getcfg.php' | grep -E '<password>|<username>'Stop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
Eliminate public-facing VPN concentrators and firewall management ports with identity-first Zero-Trust Network Access.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2021-40655) is an incorrect authorization issue (CWE-863) in the /getcfg.php page of D-Link DIR-605 B2 routers. The root cause lies in the lack of proper session validation on the script responsible for outputting system configuration data, allowing unauthenticated users to directly query sensitive endpoints.
2. Exploitation Mechanics & Attack Scenario
An attacker sends a crafted HTTP POST request targeting the /getcfg.php endpoint of the vulnerable router. By forging specific parameters in the request body, the attacker bypasses authentication checks. The server then responds with the system configuration file containing the administrator's plaintext username and password, leading to complete device takeover.
3. Infrastructure & Business Impact
This vulnerability is actively exploited in the wild and is listed in the CISA KEV catalog with a high EPSS score of over 0.87. Successful exploitation allows attackers to compromise the router, modify DNS settings to redirect traffic, or perform lateral movement to compromise internal corporate networks.
Official Vendor Advisories & References
An informtion disclosure issue exists in D-LINK-DIR-605 B2 Firmware Version : 2.01MT. An attacker can obtain a user name and password by forging a post request to the / getcfg.php page
Frequently Asked SecOps Questions (CVE-2021-40655)
FAQQ1. How critical is CVE-2021-40655 and is it actively exploited in the wild?
CVE-2021-40655 is rated CVSS 7.5 (HIGH) with a 30-day EPSS exploitation probability of 87.0%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2021-40655?
Primary impacted vendors include d-link across dir-605, dir-605_b2_firmware. Scope summary: D-Link DIR-605 B2 Firmware Version 2.01MT and earlier (End-of-Life models)
Q3. What temporary mitigations or workarounds exist for CVE-2021-40655 before patching?
[Mitigation] Immediately decommission and replace the legacy EOL device, or disable remote WAN management and restrict network access Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2021-40655
Instantly format this advisory into an executive CISO summary or engineering patch ticket.
🔗 Related Advisories in Similar Stack (d-link)
View Category →D-Link DIR-505 Router TFTP File Upload Stack-Based Buffer Overflow (CVE-2026-120189) Technical Analysis and Mitigation Guide
[Affected Scope] D-Link DIR-505 firmware version 1.10B02 and prior
Arista VeloCloud Orchestrator (VCO) Remote Code Execution and Privilege Escalation (CVE-2026-93952)
[Affected Scope] Arista VeloCloud Orchestrator (VCO) On-premise deployments.
Cisco Identity Services Engine (ISE) Critical Authentication Bypass Vulnerability (CVE-2026-76460)
[Affected Scope] Cisco Identity Services Engine (ISE) web-based management interface and API endpoints.
SonicWall SMA1000 Work Place Pre-Authentication Server-Side Request Forgery (SSRF) Vulnerability (CVE-2026-83548)
[Affected Scope] SonicWall SMA1000 Series Appliance Work Place interface
Subscribe to Daily Vulnerability Briefings & KEV Alerts
Concise morning briefings for SecOps, DevSecOps, and SRE teams covering newly exploited CVEs and mitigation priorities.