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CVE-2026-42376— D-Link DIR-456U A1 Hardcoded Telnet Backdoor Credentials

Quick assessment

Affected
D-Link DIR-456U Firmware
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

D-Link DIR-456U是中国友讯（D-Link）公司的一款无线路由器。 D-Link DIR-456U Hardware Revision A1存在信任管理问题漏洞，该漏洞源于硬编码的telnet后门，可能导致本地网络上的未认证攻击者获得root shell并完全控制设备。

CVSS 9.8 · Critical EPSS 0.85% · P57

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
D-Link DIR-456U Firmware A1 affected
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I. Basic Information for CVE-2026-42376

Vulnerability Information
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Vulnerability Title
D-Link DIR-456U A1 Hardcoded Telnet Backdoor Credentials
Source: CVE Program / CVE List V5
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
使用硬编码的凭证
Source: CVE Program / CVE List V5
Vulnerability Title
D-Link DIR-456U 信任管理问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
D-Link DIR-456U是中国友讯（D-Link）公司的一款无线路由器。 D-Link DIR-456U Hardware Revision A1存在信任管理问题漏洞，该漏洞源于硬编码的telnet后门，可能导致本地网络上的未认证攻击者获得root shell并完全控制设备。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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Affected Products

Vendor Product Affected Versions CPE Subscribe
D-Link DIR-456U Firmware A1 cpe:2.3:o:dlink:dir-456u_firmware:*:*:*:*:*:*:*:*

II. Public POCs for CVE-2026-42376

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III. Intelligence Information for CVE-2026-42376

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News Coverage for CVE-2026-42376 (1)

Same Patch Batch · D-Link · 2026-05-04 · 5 CVEs total

CVE-2026-42375 9.8 CRITICAL D-Link DIR-600L A1 Hardcoded Telnet Backdoor Credentials
CVE-2026-42374 9.8 CRITICAL D-Link DIR-600L B1 Hardcoded Telnet Backdoor Credentials
CVE-2026-42373 9.8 CRITICAL D-Link DIR-605L B2 Hardcoded Telnet Backdoor Credentials
CVE-2026-42372 8.8 HIGH D-Link DIR-605L A1 Hardcoded Telnet Backdoor Credentials

IV. Related Vulnerabilities

Same vendor: D-Link
Same weakness: CWE-798

V. Comments for CVE-2026-42376

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