CVE-2026-42376 — CRITICAL (9.8)

Vulnerability Description

D-Link DIR-456U Hardware Revision A1 (End-of-Life, EOL) contains a hardcoded telnet backdoor. The device starts a telnet daemon at boot via /etc/init0.d/S80telnetd.sh with the username "Alphanetworks" and the static password "whdrv01_dlob_dir456U" read from /etc/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.

CVSS Score

9.8

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

UNCHANGED

Confidentiality

HIGH

Integrity

HIGH

Availability

HIGH

Affected Products

Vendor	Product	Versions
Dlink	Dir-456U Firmware	-
Dlink	Dir-456U	a1

Related Weaknesses (CWE)

CWE-798

References

https://www.securin.io/zero-day/cve-2026-42376-hardcoded-telnet-backdoor-in-d-liExploitThird Party Advisory
https://www.securin.io/zero-day/cve-2026-42376-hardcoded-telnet-backdoor-in-d-liExploitThird Party Advisory

FAQ

What is CVE-2026-42376?

CVE-2026-42376 is a vulnerability with a CVSS score of 9.8 (CRITICAL). D-Link DIR-456U Hardware Revision A1 (End-of-Life, EOL) contains a hardcoded telnet backdoor. The device starts a telnet daemon at boot via /etc/init0.d/S80telnetd.sh with the username "Alphanetworks"...

How severe is CVE-2026-42376?

CVE-2026-42376 has been rated CRITICAL with a CVSS base score of 9.8/10. This is considered a critical vulnerability requiring immediate attention.

Is there a patch for CVE-2026-42376?

Check the references section above for vendor advisories and patch information. Affected products include: Dlink Dir-456U Firmware, Dlink Dir-456U.