Is CVE-2026-42376 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-42376 being exploited in the wild.

How severe is CVE-2026-42376?

Critical severity, with a CVSS score of 9.8, published 4 May 2026.

Which products and versions are affected?

D-Link DIR-456U Hardware Revision A1 (All firmware versions).

Is there a fix for CVE-2026-42376?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-42376 attacked?

It is attacked over the network or from the adjacent network, in a network appliance.

Am I affected by CVE-2026-42376?

Check whether you run Dlink Dir-456u or Dlink Dir-456u Firmware. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-42376: D-Link DIR-456U hardcoded telnet backdoor

CVE-2026-42376 · Severity: critical · CVSS 9.8 · Published 2026-05-04

The D-Link DIR-456U router contains a permanent security backdoor that allows anyone on the local network to take full control of the device. By using a secret, built-in username and password, an attacker can access the router's administrative functions without your permission. Because this product is at its end-of-life, the manufacturer will not be providing any security updates to fix this issue. Using this device poses a significant risk to your network security and privacy.

Vendors: Dlink.

Quick answers

Is CVE-2026-42376 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-42376 being exploited in the wild.
How severe is CVE-2026-42376?: Critical severity, with a CVSS score of 9.8, published 4 May 2026.
Which products and versions are affected?: D-Link DIR-456U Hardware Revision A1 (All firmware versions).
Is there a fix for CVE-2026-42376?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-42376 attacked?: It is attacked over the network or from the adjacent network, in a network appliance.
Am I affected by CVE-2026-42376?: Check whether you run Dlink Dir-456u or Dlink Dir-456u Firmware. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The D-Link DIR-456U Hardware Revision A1 contains a hardcoded telnet backdoor (CWE-798) originating from its ODM, Alpha Networks. The device unconditionally executes a boot script (/etc/init0.d/S80telnetd.sh) that starts a telnet daemon with a custom login binary. This binary validates credentials against a hardcoded username ('Alphanetworks') and a static password ('whdrv01_dlob_dir456U') stored in the firmware. An attacker on the local network (LAN or WLAN) can connect to TCP port 23 to obtain a root shell with full administrative privileges. As the device is End-of-Life (EOL), no patches are available, and the manufacturer recommends replacing the hardware.

Affected products

D-Link DIR-456U Hardware Revision A1 (All firmware versions)

Timeline

2026-04-20: other: Vulnerability identified and validated via QEMU
2026-04-20: other: Reported to vendor
2026-04-21: other: Vendor confirmed EOL status; no fix will be issued
2026-05-04: advisory: Public advisory and CVE published

References

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

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