D-Link DIR-600L B1 /bin/telnetd.sh strcmp hard-coded credentials

Summaryinfo

A vulnerability classified as critical has been found in D-Link DIR-600L B1. This affects the function strcmp of the file /bin/telnetd.sh. The manipulation leads to hard-coded credentials. This vulnerability only affects products that are no longer supported by the maintainer. This vulnerability is traded as CVE-2026-42374. Access to the local network is required for this attack to succeed. There is no exploit available.

Detailsinfo

A vulnerability was found in D-Link DIR-600L B1 (version now known). It has been rated as critical. This issue affects the function strcmp of the file /bin/telnetd.sh. The manipulation with an unknown input leads to a hard-coded credentials vulnerability. Using CWE to declare the problem leads to CWE-798. The product contains hard-coded credentials, such as a password or cryptographic key, which it uses for its own inbound authentication, outbound communication to external components, or encryption of internal data. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

D-Link DIR-600L Hardware Revision B1 (End-of-Life) contains a hardcoded telnet backdoor. The device starts a telnet daemon at boot via /bin/telnetd.sh with the username "Alphanetworks" and the static password "wrgn61_dlwbr_dir600L" read from /etc/alpha_config/image_sign. The custom telnetd binary accepts a -u user:password flag, and the custom login binary uses strcmp() to validate credentials. Successful authentication grants an unauthenticated attacker on the local network a root shell with full administrative control.  The device has reached End-of-Life (EOL) and will not receive patches.

The weakness was shared by Arjun Basnet. The advisory is shared at securin.io. The identification of this vulnerability is CVE-2026-42374 since 04/27/2026. The exploitation is known to be easy. Access to the local network is required for this attack to succeed. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available. The price for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 05/04/2026). MITRE ATT&CK project uses the attack technique T1110.001 for this issue.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-27025). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

Type

• Router Operating System

Vendor

• D-Link

Name

• DIR-600L B1

License

• commercial

Support

• end of life

Website

• Vendor: https://www.dlink.com/

CPE 2.3info

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CPE 2.2info

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Entryinfo

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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