CVE-2026-42376: D-Link DIR-456U Hardware Revision A1 (End-of-Life, EOL) contains a hardcoded telnet backdoor

This week

CRITICAL 9.8REMOTEMITIGATE

CVE-2026-42376 is a critical-severity flaw (CVSS 9.8) affecting dir-456u firmware. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 unauth

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 60%)
CISA exploited list	No
Weakness	CWE-798
Published	2026-05-04
Last modified	2026-10-26

Publisher (CNA): securin · Vendor: dlink

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-04 17:16 UTCPublished CVE record published
2026-10-26 19:10 UTCUpdated Record last modified

dlink dir-456u firmware MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-42376?

dir-456u firmware: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-42376 being exploited?

CVE-2026-42376 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-42376 affect?

CVE-2026-42376 affects dir-456u firmware. Severity is critical (CVSS 9.8). 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_d

How urgent is CVE-2026-42376?

Priority 54/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

D-Link vulnerabilities

References

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