{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-42376", "assignerOrgId": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "state": "PUBLISHED", "assignerShortName": "securin", "dateReserved": "2026-04-27T06:21:56.902Z", "datePublished": "2026-05-04T16:03:59.473Z", "dateUpdated": "2026-05-04T16:32:10.149Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "shortName": "securin", "dateUpdated": "2026-05-04T16:03:59.473Z"}, "title": "D-Link DIR-456U A1 Hardcoded Telnet Backdoor Credentials", "datePublic": "2026-04-24T00:00:00.000Z", "problemTypes": [{"descriptions": [{"lang": "en", "cweId": "CWE-798", "description": "CWE-798 Use of Hard-coded Credentials", "type": "CWE"}]}], "affected": [{"vendor": "D-Link", "product": "DIR-456U Firmware", "platforms": ["MIPS32 Little-Endian"], "versions": [{"status": "affected", "version": "A1", "versionType": "custom"}], "defaultStatus": "affected", "cpes": ["cpe:2.3:o:dlink:dir-456u_firmware:*:*:*:*:*:*:*:*"]}], "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.", "supportingMedia": [{"type": "text/html", "base64": false, "value": "<p>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.</p>"}]}], "tags": ["unsupported-when-assigned"], "references": [{"url": "https://www.securin.io/zero-day/cve-2026-42376-hardcoded-telnet-backdoor-in-d-link-dir-456u-a1-end-of-life-", "name": "D-Link DIR-456U A1 Hardcoded Telnet Backdoor - Securin Advisory"}], "metrics": [{"format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}], "cvssV3_1": {"version": "3.1", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH", "baseSeverity": "CRITICAL", "baseScore": 9.8, "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"}}], "workarounds": [{"lang": "en", "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).", "supportingMedia": [{"type": "text/html", "base64": false, "value": "<p>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).</p>"}]}], "credits": [{"lang": "en", "value": "Arjun Basnet from Securin Labs", "type": "finder"}], "source": {"discovery": "EXTERNAL"}, "x_generator": {"engine": "Vulnogram 1.0.2"}}, "adp": [{"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"]}], "metrics": [{"other": {"type": "ssvc", "content": {"timestamp": "2026-05-04T16:32:05.738044Z", "id": "CVE-2026-42376", "options": [{"Exploitation": "poc"}, {"Automatable": "yes"}, {"Technical Impact": "total"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-05-04T16:32:10.149Z"}}]}}

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