Vulnerability-Lookup

GHSA-8FMW-7P6G-WW4Q

Vulnerability from github – Published: 2026-05-04 18:30 – Updated: 2026-05-04 18:30

Details

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.

Severity ?

9.8 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [],
  "aliases": [
    "CVE-2026-42376"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-798"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-05-04T17:16:26Z",
    "severity": "CRITICAL"
  },
  "details": "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.",
  "id": "GHSA-8fmw-7p6g-ww4q",
  "modified": "2026-05-04T18:30:31Z",
  "published": "2026-05-04T18:30:31Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-42376"
    },
    {
      "type": "WEB",
      "url": "https://www.securin.io/zero-day/cve-2026-42376-hardcoded-telnet-backdoor-in-d-link-dir-456u-a1-end-of-life-"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-42376 (GCVE-0-2026-42376)

Vulnerability from cvelistv5 – Published: 2026-05-04 16:03 – Updated: 2026-05-04 16:32 Unsupported When Assigned

Title

D-Link DIR-456U A1 Hardcoded Telnet Backdoor Credentials

Summary

Severity ?

9.8 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE

CWE-798 - Use of Hard-coded Credentials

Assigner

securin

References

URL

Tags

https://www.securin.io/zero-day/cve-2026-42376-ha…

Impacted products

	Vendor	Product	Version
	D-Link	DIR-456U Firmware	Affected: A1 (custom) cpe:2.3:o:dlink:dir-456u_firmware::::::::

Date Public ?

2026-04-24 00:00

Credits

Arjun Basnet from Securin Labs

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-42376",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-05-04T16:32:05.738044Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-05-04T16:32:10.149Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://www.securin.io/zero-day/cve-2026-42376-hardcoded-telnet-backdoor-in-d-link-dir-456u-a1-end-of-life-"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "cpes": [
            "cpe:2.3:o:dlink:dir-456u_firmware:*:*:*:*:*:*:*:*"
          ],
          "defaultStatus": "affected",
          "platforms": [
            "MIPS32 Little-Endian"
          ],
          "product": "DIR-456U Firmware",
          "vendor": "D-Link",
          "versions": [
            {
              "status": "affected",
              "version": "A1",
              "versionType": "custom"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Arjun Basnet from Securin Labs"
        }
      ],
      "datePublic": "2026-04-24T00:00:00.000Z",
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "\u003cp\u003eD-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.\u003c/p\u003e"
            }
          ],
          "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": "\u003cp\u003eThis 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).\u003c/p\u003e"
            }
          ],
          "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"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-8FMW-7P6G-WW4Q

CVE-2026-42376 (GCVE-0-2026-42376)

Tags

Sightings

Nomenclature