CVE-2026-42376Public exploitNetwork attack vector

Unauthenticated root shell via hardcoded Telnet credentials

Published May 4, 2026 · Updated May 4, 2026

Hardcoded credentials in D-Link DIR-456U Firmware A1 allow remote attackers on the local network to obtain a root shell over Telnet. The boot script /etc/init0.d/S80telnetd.sh unconditionally starts telnetd on br0 with a fixed username and a password read from /etc/config/image_sign, while login validates supplied credentials with strcmp(). LAN or Wi-Fi reachability to TCP port 23 is sufficient, granting full administrative control without prior authentication or user interaction.

CVSS severity9.8
Critical
EPSS probability0.46%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Hardcoded credentials in D-Link DIR-456U Firmware A1 allow remote attackers on the local network to obtain a root shell over Telnet. The boot script /etc/init0.d/S80telnetd.sh unconditionally starts telnetd on br0 with a fixed username and a password read from /etc/config/image_sign, while login validates supplied credentials with strcmp(). LAN or Wi-Fi reachability to TCP port 23 is sufficient, granting full administrative control without prior authentication or user interaction.

The record

CVE
CVE-2026-42376
Published
May 4, 2026
Updated
May 4, 2026
Vendor
D-Link
Product
DIR-456U Firmware
Classifications
CWE-798, T1078
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 4, 2026CVE publishedPublication date reported by the CVE source.
  2. May 4, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=A1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

D-Link · DIR-456U Firmwareversion=A1

Published CVSS scores

9.8SecurinCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-798Use of Hard-coded Credentials
T1078Valid Accounts

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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