D-Link DIR-605L Hardcoded Telnet Backdoor Analysis CVE-2026-42372

Vulnerability Summary: CVE-2026-42372 Vulnerability Overview Vulnerability ID: CVE-2026-42372 Vulnerability Name: Hardcoded Telnet Backdoor in D-Link DIR-605L A1 Firmware Severity: Critical Vulnerability Types: CWE-798 (Use of Hard-coded Credentials), CWE-912 (Hidden Malicious Code), CWE-259 (Password in Clear Text) Affected Product: D-Link DIR-605L Hardware Revision A1 (End-of-Life) Description: A hardcoded Telnet backdoor exists within the firmware file system and is identical across all DIR-605L A1 devices. Upon successful authentication, it provides a root shell with full administrative privileges. The backdoor script executes unconditionally at startup, with no user interface option available to disable it. Impact Scope Attack Scenario: The attacker is located on the same Local Area Network (LAN) or WiFi network. Attack Vector: Connect to the router's Telnet service (TCP port 23) and input the hardcoded credentials to obtain a root shell. No authentication, session tokens, or CSRF tokens are required. Potential Impact: Execute arbitrary commands as root. Read/modify all router configurations, including WiFi passwords and DNS settings. Intercept, redirect, or modify all network traffic. Install persistent malware or perform lateral movement within the internal network. Remediation Vendor Status: This product has reached End-of-Life (EOL); D-Link will not release a patch. Recommended Actions: 1. Immediately replace the device with a currently supported router model. 2. Temporary mitigation: Terminate the process via the backdoor and block port 23 (note: this will fail after a reboot). 3. Do not use this device in networks handling sensitive security data. Proof of Concept (POC) Vulnerable Code Snippet ( ) Exploitation Steps 1. Connect: Telnet to the router's default LAN IP (e.g., ). 2. Enter Username: 3. Enter Password: (firmware-specific password) 4. Result**: Immediate access to a root shell.

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D-Link DIR-605L Hardcoded Telnet Backdoor Analysis CVE-2026-42372