CVE-2026-42376

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2026-05-04. NVD baseline CVSS 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Elevated
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 9.8Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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
EG Score
9.8(medium)
EG Risk
75(Attend)
EG Risk 75/100SSVC: Attend

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation40% × 40%
Automatability100% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
0%
EPSS %ILE
39%
KEV
Not listed

Published

May 4, 2026

Last Modified

May 11, 2026

Advisory Details (1)

Auto-updated Sep 9, 2026
🔬 Proof of concept available. No patch confirmed yet.
generic🟡 PoC Available

CVE-2026-42376: Hardcoded Telnet Backdoor in D-Link |… | Securin

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

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 6× in last 7d / 29× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 274 total refreshes for this CVE.

  1. 2026-09-13 16:47 UTCEPSS rescore
  2. 2026-09-12 15:01 UTCEPSS rescore
  3. 2026-09-11 14:53 UTCEPSS rescore
  4. 2026-09-11 09:37 UTCEPSS rescore
  5. 2026-09-10 09:34 UTCEPSS rescore
  6. 2026-09-08 22:00 UTCEPSS rescore
  7. 2026-09-07 16:01 UTCEPSS rescore
  8. 2026-09-06 13:47 UTCEPSS rescore
  9. 2026-09-04 05:06 UTCEPSS rescore
  10. 2026-09-02 14:12 UTCEPSS rescore
  11. 2026-09-01 13:54 UTCEPSS rescore
  12. 2026-08-30 19:17 UTCEPSS rescore
  13. 2026-08-30 01:22 UTCEPSS rescore
  14. 2026-08-28 21:41 UTCEPSS rescore
  15. 2026-08-27 14:25 UTCEPSS rescore
  16. 2026-08-26 14:46 UTCEPSS rescore
  17. 2026-08-25 13:49 UTCEPSS rescore
  18. 2026-08-23 21:18 UTCEG score recompute
  19. 2026-08-23 21:18 UTCGHSA enrichment
  20. 2026-08-23 00:19 UTCEPSS rescore
  21. 2026-08-21 23:49 UTCEPSS rescore
  22. 2026-08-20 22:55 UTCEPSS rescore
  23. 2026-08-19 17:03 UTCEPSS rescore
  24. 2026-08-18 13:48 UTCEPSS rescore
  25. 2026-08-17 13:47 UTCEPSS rescore
Show 75 more
  1. 2026-08-17 13:12 UTCEG score recompute
  2. 2026-08-17 13:12 UTCGHSA enrichment
  3. 2026-08-16 14:56 UTCEPSS rescore
  4. 2026-08-16 09:15 UTCGHSA enrichment
  5. 2026-08-16 05:03 UTCEG score recompute
  6. 2026-08-16 05:03 UTCGHSA enrichment
  7. 2026-08-16 02:14 UTCEPSS rescore
  8. 2026-08-15 01:30 UTCEPSS rescore
  9. 2026-08-15 00:46 UTCGHSA enrichment
  10. 2026-08-14 20:33 UTCGHSA enrichment
  11. 2026-08-14 16:16 UTCGHSA enrichment
  12. 2026-08-14 12:03 UTCGHSA enrichment
  13. 2026-08-14 07:51 UTCGHSA enrichment
  14. 2026-08-14 03:38 UTCEG score recompute
  15. 2026-08-14 03:38 UTCGHSA enrichment
  16. 2026-08-13 22:00 UTCEPSS rescore
  17. 2026-08-13 10:51 UTCGHSA enrichment
  18. 2026-08-13 06:36 UTCGHSA enrichment
  19. 2026-08-13 01:42 UTCGHSA enrichment
  20. 2026-08-12 21:29 UTCGHSA enrichment
  21. 2026-08-12 17:16 UTCEG score recompute
  22. 2026-08-12 17:16 UTCGHSA enrichment
  23. 2026-08-12 13:51 UTCEPSS rescore
  24. 2026-08-12 00:36 UTCGHSA enrichment
  25. 2026-08-11 20:23 UTCGHSA enrichment
  26. 2026-08-11 16:08 UTCEG score recompute
  27. 2026-08-11 16:08 UTCGHSA enrichment
  28. 2026-08-11 13:43 UTCEPSS rescore
  29. 2026-08-11 05:52 UTCGHSA enrichment
  30. 2026-08-11 01:40 UTCEG score recompute
  31. 2026-08-11 01:40 UTCGHSA enrichment
  32. 2026-08-11 00:00 UTCEPSS rescore
  33. 2026-08-10 13:58 UTCGHSA enrichment
  34. 2026-08-10 09:36 UTCGHSA enrichment
  35. 2026-08-10 05:23 UTCGHSA enrichment
  36. 2026-08-10 01:11 UTCGHSA enrichment
  37. 2026-08-09 20:57 UTCGHSA enrichment
  38. 2026-08-09 16:45 UTCEG score recompute
  39. 2026-08-09 16:45 UTCGHSA enrichment
  40. 2026-08-09 13:46 UTCEPSS rescore
  41. 2026-08-09 12:32 UTCGHSA enrichment
  42. 2026-08-09 06:58 UTCGHSA enrichment
  43. 2026-08-09 02:45 UTCEG score recompute
  44. 2026-08-09 02:45 UTCGHSA enrichment
  45. 2026-08-08 16:37 UTCEPSS rescore
  46. 2026-08-08 12:42 UTCGHSA enrichment
  47. 2026-08-08 08:28 UTCGHSA enrichment
  48. 2026-08-08 04:15 UTCGHSA enrichment
  49. 2026-08-08 00:02 UTCGHSA enrichment
  50. 2026-08-07 19:49 UTCEG score recompute
  51. 2026-08-07 19:49 UTCGHSA enrichment
  52. 2026-08-07 15:36 UTCGHSA enrichment
  53. 2026-08-07 11:23 UTCGHSA enrichment
  54. 2026-08-07 02:14 UTCGHSA enrichment
  55. 2026-08-06 21:13 UTCGHSA enrichment
  56. 2026-08-06 17:00 UTCEG score recompute
  57. 2026-08-06 17:00 UTCGHSA enrichment
  58. 2026-08-06 13:46 UTCEPSS rescore
  59. 2026-08-06 11:08 UTCGHSA enrichment
  60. 2026-08-06 06:55 UTCGHSA enrichment
  61. 2026-08-06 02:42 UTCGHSA enrichment
  62. 2026-08-05 22:29 UTCEG score recompute
  63. 2026-08-05 22:29 UTCGHSA enrichment
  64. 2026-08-05 19:17 UTCEPSS rescore
  65. 2026-08-04 15:10 UTCEPSS rescore
  66. 2026-08-04 10:38 UTCEPSS rescore
  67. 2026-08-04 04:29 UTCGHSA enrichment
  68. 2026-08-04 00:16 UTCGHSA enrichment
  69. 2026-08-03 20:02 UTCEG score recompute
  70. 2026-08-03 20:02 UTCGHSA enrichment
  71. 2026-08-03 10:36 UTCEPSS rescore
  72. 2026-08-03 02:52 UTCGHSA enrichment
  73. 2026-08-02 22:33 UTCGHSA enrichment
  74. 2026-08-02 18:20 UTCGHSA enrichment
  75. 2026-08-02 14:06 UTCGHSA enrichment

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Frequently asked(5)

What is CVE-2026-42376?
CVE-2026-42376 is a critical vulnerability published on May 4, 2026. 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 "whdrv01dlobdir456U" read from /etc/config/image_sign. The custom telnetd…
When was CVE-2026-42376 disclosed?
CVE-2026-42376 was first published in the National Vulnerability Database on May 4, 2026, with the most recent update on May 11, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-42376 actively exploited?
CVE-2026-42376 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 61.3% of all scored CVEs.
What is the CVSS score of CVE-2026-42376?
CVE-2026-42376 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2026-42376?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-42376, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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