CVE-2026-42376 | D-Link DIR-456U Hardware Revision A1 (End-of-Life, EOL) cont… | CVSS 9.8 CRITICAL

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.

Metadata

CVE ID: CVE-2026-42376
State: PUBLISHED
Assigner: securin
Reserved: 2026-04-27 06:21 UTC
Published: 2026-05-04 16:03 UTC
Last updated: 2026-05-04 16:32 UTC
Primary CWE: CWE-798
CWE-798 Use of Hard-coded Credentials
Vendor / Product: D-Link / DIR-456U Firmware
Sources: cve.org · NVD

Severity & Metrics

9.8 CRITICAL CVSS 3.1

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

SSVC — CISA Coordinator

Exploitation: PoC
Automatable: yes
Tech. Impact: total

Affected products (1)

Vendor	Product	Platform	Versions
D-Link	DIR-456U Firmware	MIPS32 Little-Endian	A1

Weakness (CWE)

CWE	Source	Description
CWE-798	cna	CWE-798 Use of Hard-coded Credentials

CVSS scores (1)

Score	Severity	Version	Source	Vector
9.8	CRITICAL	3.1	cna	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References (1)

D-Link DIR-456U A1 Hardcoded Telnet Backdoor - Securin Advisory https://www.securin.io/zero-day/cve-2026-42376-hardcoded-telnet-backdoor-in-d-link-dir-456u-a1-end-of-life-