Security researchers have discovered a critical vulnerability in popular D-Link router models that exposes millions of devices to potential remote attacks.
CVE-2025-46176, disclosed three days ago, reveals hardcoded credentials embedded within the Telnet service of affected routers, allowing attackers to execute arbitrary commands remotely through firmware analysis.
The vulnerability affects two widely deployed consumer router models: the D-Link DIR-605L version 2.13B01 and the DIR-816L version 2.06B01.
The vulnerability was uncovered through systematic firmware analysis using binwalk, a popular tool for extracting and analyzing firmware images.
Researchers successfully extracted the SquashFS file system from both affected router models, revealing the underlying architecture that contains the security flaw.
The investigation began when security experts searched for references to “Alphanetworks” within the extracted file systems, which led them to discover the telnetd initialization script located at ./bin/telnetd.sh.
This discovery method highlights the importance of firmware security auditing and demonstrates how seemingly innocuous references can lead to the identification of serious security vulnerabilities.
The use of binwalk for firmware extraction has become a standard practice in security research, allowing experts to examine the internal workings of embedded devices that consumers typically cannot access.
Hardcoded Credential Issue
The core vulnerability lies in the telnetd service initialization process, where both affected router models configure a user account named “Alphanetworks” with a password derived from a system variable called $image_sign.
This password is not randomly generated or user-configurable but instead reads from a static file located at ./etc/alpha_config/image_sign within the router’s file system.
The security flaw becomes evident when examining the telnetd.sh script, which automatically establishes this user account with predetermined credentials every time the service starts.
The image_sign file contains a hardcoded password that remains consistent across all devices of the same model and firmware version, creating a universal backdoor that attackers can exploit once they determine the credentials for any single device.
This implementation represents a fundamental security oversight in embedded device design, where manufacturer-intended access mechanisms become unintended attack vectors when discovered by malicious actors.
Impact and Security Implications
The implications of CVE-2025-46176 extend far beyond simple unauthorized access, as the vulnerability enables complete remote code execution on affected devices.
Organizations should also conduct network security assessments to identify and remediate any vulnerable devices within their infrastructure.
Once attackers gain access through the hardcoded Telnet credentials, they can execute arbitrary commands with system-level privileges, potentially compromising the entire network infrastructure connected to these routers.
According to the Report, The widespread deployment of the affected D-Link models amplifies the security risk, as millions of home and small business networks could be vulnerable to attack.
Attackers could leverage compromised routers for various malicious activities, including network surveillance, traffic interception, botnet recruitment, and lateral movement within connected networks.
The vulnerability also raises broader questions about embedded device security practices and the need for mandatory security auditing in consumer networking equipment.
The discovery of hardcoded credentials in production firmware suggests inadequate security review processes during device development and highlights the ongoing challenge of securing Internet of Things devices.
Users of affected D-Link router models should immediately check for firmware updates and consider disabling Telnet services if not required for legitimate network administration purposes.
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