PT-2026-36837 · D Link · Dir-456U

Arjun Basnet · Published 2026-04-20 · Updated 2026-05-13 · CVE-2026-42376

Positive Technologies (AI Summary)

CVSS v3.1

10

Critical

Base vector

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

Name of the Vulnerable Software and Affected Versions D-Link DIR-456U Hardware Revision A1

Description The device contains a hardcoded telnet backdoor. At boot, a telnet daemon is started via the script '/etc/init0.d/S80telnetd.sh' using the username "Alphanetworks" and a static password "whdrv01 dlob dir456U" stored in '/etc/config/image sign'. The custom telnetd binary utilizes a -u user:password flag, and the login binary employs the strcmp() function to validate credentials. An unauthenticated attacker on the local network can use these credentials to gain a root shell, providing full administrative control over the device.

Recommendations At the moment, there is no information about a newer version that contains a fix for this vulnerability.

Exploit

Using Hardcoded Credentials

Weakness Enumeration

CWE-798

CWE-259

Related Identifiers

BDU:2026-06321

CVE-2026-42376

Affected Products

Dir-456U

References · 11

• 🔥 https://securin.io/zero-day/cve-2026-42376-hardcoded-telnet-backdoor-in-d-link-dir-456u-a1-end-of-life- · Exploit
• https://nvd.nist.gov/vuln/detail/CVE-2026-42376 · Security Note
• https://bdu.fstec.ru/vul/2026-06321 · Security Note
• https://twitter.com/lyrie_ai/status/2054449298507534543 · Twitter Post
• https://twitter.com/vuldb/status/2051346661021229257 · Twitter Post
• https://twitter.com/VulmonFeeds/status/2051419015197704380 · Twitter Post
• https://t.me/CVEtracker/52642 · Telegram Post
• https://twitter.com/lyrie_ai/status/2054449299371483418 · Twitter Post
• https://twitter.com/lyrie_ai/status/2054449300189425688 · Twitter Post
• https://t.me/cveNotify/163092 · Telegram Post
• https://twitter.com/lyrie_ai/status/2054449301045100661 · Twitter Post