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.
"}],"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."}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":9.8,"baseSeverity":"CRITICAL","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","version":"3.1"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-798","description":"CWE-798 Use of Hard-coded Credentials","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-05-04T16:03:59.473Z","orgId":"33c584b5-0579-4c06-b2a0-8d8329fcab9c","shortName":"securin"},"references":[{"name":"D-Link DIR-456U A1 Hardcoded Telnet Backdoor - Securin Advisory","url":"https://www.securin.io/zero-day/cve-2026-42376-hardcoded-telnet-backdoor-in-d-link-dir-456u-a1-end-of-life-"}],"source":{"discovery":"EXTERNAL"},"tags":["unsupported-when-assigned"],"title":"D-Link DIR-456U A1 Hardcoded Telnet Backdoor Credentials","workarounds":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"This product is End-of-Life (EOL) and will NOT receive patches. Users should replace the device. Temporary: connect via backdoor and run \"killall telnetd\" and \"iptables -A INPUT -p tcp --dport 23 -j DROP\" (lost on reboot).
"}],"value":"This product is End-of-Life (EOL) and will NOT receive patches. Users should replace the device. Temporary: connect via backdoor and run \"killall telnetd\" and \"iptables -A INPUT -p tcp --dport 23 -j DROP\" (lost on reboot)."}],"x_generator":{"engine":"Vulnogram 1.0.2"}}},"cveMetadata":{"assignerOrgId":"33c584b5-0579-4c06-b2a0-8d8329fcab9c","assignerShortName":"securin","cveId":"CVE-2026-42376","datePublished":"2026-05-04T16:03:59.473Z","dateReserved":"2026-04-27T06:21:56.902Z","dateUpdated":"2026-05-04T16:32:10.149Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-05-04 17:16:26","lastModifiedDate":"2026-05-05 19:32:23","problem_types":["CWE-798","CWE-798 CWE-798 Use of Hard-coded Credentials"],"metrics":{"cvssMetricV31":[{"source":"33c584b5-0579-4c06-b2a0-8d8329fcab9c","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":3.9,"impactScore":5.9}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"42376","Ordinal":"1","Title":"D-Link DIR-456U A1 Hardcoded Telnet Backdoor Credentials","CVE":"CVE-2026-42376","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"42376","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"D-Link DIR-456U A1 Hardcoded Telnet Backdoor Credentials"}]}}}