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

Source: https://junglewise.ai/threats/cve-2026-42376-d-link-dir-456u-hardcoded-telnet-backdoor  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-04. Updated: 2026-05-11  
License: CC BY 4.0 with a link back

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