CVE-2026-42376

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 v3 9.8 CRITICAL

9.8^/10

CVSS v3 : CRITICAL

Vector :

Exploitability : 3.9 / Impact : 5.9

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://www.securin.io/zero-day/cve-2026-42376-hardcoded-telnet-backdoor-in-d-link-dir-456u-a1-end-of-life-	Exploit Third Party Advisory
https://www.securin.io/zero-day/cve-2026-42376-hardcoded-telnet-backdoor-in-d-link-dir-456u-a1-end-of-life-	Exploit Third Party Advisory

Configurations

Configuration 1 (hide)

AND

cpe:2.3:o:dlink:dir-456u_firmware:-:*:*:*:*:*:*:*

cpe:2.3:h:dlink:dir-456u:a1:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-05-04 17:16

Updated : 2026-06-17 10:47

NVD link : CVE-2026-42376

Mitre link : CVE-2026-42376

CVE.ORG link : CVE-2026-42376

JSON object : View

Products Affected

dlink

dir-456u_firmware
dir-456u

CWE

CWE-798

Use of Hard-coded Credentials

{"id": "CVE-2026-42376", "cveTags": [{"tags": ["unsupported-when-assigned"], "sourceIdentifier": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"}], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-42376", "role": "CISA Coordinator", "options": [{"exploitation": "poc"}, {"automatable": "yes"}, {"technicalImpact": "total"}], "version": "2.0.3", "timestamp": "2026-05-04T16:32:05.738044Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 9.8, "attackVector": "NETWORK", "baseSeverity": "CRITICAL", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H", "integrityImpact": "HIGH", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "NONE", "confidentialityImpact": "HIGH"}, "impactScore": 5.9, "exploitabilityScore": 3.9}]}, "affected": [{"source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "affectedData": [{"cpes": ["cpe:2.3:o:dlink:dir-456u_firmware:*:*:*:*:*:*:*:*"], "vendor": "D-Link", "product": "DIR-456U Firmware", "versions": [{"status": "affected", "version": "A1", "versionType": "custom"}], "platforms": ["MIPS32 Little-Endian"], "defaultStatus": "affected"}]}], "published": "2026-05-04T17:16:26.000", "references": [{"url": "https://www.securin.io/zero-day/cve-2026-42376-hardcoded-telnet-backdoor-in-d-link-dir-456u-a1-end-of-life-", "tags": ["Exploit", "Third Party Advisory"], "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"}, {"url": "https://www.securin.io/zero-day/cve-2026-42376-hardcoded-telnet-backdoor-in-d-link-dir-456u-a1-end-of-life-", "tags": ["Exploit", "Third Party Advisory"], "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Secondary", "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "description": [{"lang": "en", "value": "CWE-798"}]}], "descriptions": [{"lang": "en", "value": "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."}], "lastModified": "2026-06-17T10:47:46.167", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:o:dlink:dir-456u_firmware:-:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "76502864-95D1-417C-B210-C0AE12E7FA05"}], "operator": "OR"}, {"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:h:dlink:dir-456u:a1:*:*:*:*:*:*:*", "vulnerable": false, "matchCriteriaId": "1DA2448C-DD05-4AF5-A441-F9EA84185AFA"}], "operator": "OR"}], "operator": "AND"}], "sourceIdentifier": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"}