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CVE-2026-38577 – Hardcoded Credentials Leading to Root Access – Tenda HG21 V4.0.0-260302

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Summary

CVE-2026-38577 is a critical vulnerability (CWE-798: Use of Hard-coded Credentials) affecting the Tenda HG21 router running firmware V4.0.0-260302. The Admin account on affected devices uses insecure hardcoded credentials, allowing an unauthenticated remote attacker to gain root-level access to the device. The flaw carries a CVSS v3.1 base score of 9.8 (Critical).

Technical details

  • Root cause: The Admin account on affected firmware relies on hardcoded (embedded, non-configurable) credentials rather than credentials set or rotated by the device owner.
  • Trigger conditions: No prior authentication or user interaction is required; an attacker only needs network access to the device’s management interface.
  • Attack vector: Network (remote), with low attack complexity and no privileges required.
  • Impact: Successful exploitation grants root access to the device, resulting in complete loss of confidentiality, integrity, and availability of the device and any traffic/network it controls.

Affected software

  • Tenda HG21, firmware version V4.0.0-260302

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: No official Tenda patch or advisory has been identified for this CVE at the time of writing. Check the Tenda support site for a firmware update superseding V4.0.0-260302 and apply it as soon as it is available.
  • If no patch is available:
    • Remove the device’s administrative/management interface from direct internet exposure; restrict access to trusted internal networks or VPN only.
    • Place the device behind a firewall that blocks inbound access to management ports/services from the WAN.
    • Monitor for unexpected administrative logins or configuration changes.
    • Where feasible, replace or isolate affected devices until a vendor fix is confirmed.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Page title: Tenda Web Master
  • Raw response body: an anchor element with a brand class and title="Tenda"

References

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Map your entire attack surface (continously)

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2

Monitor for new CVEs

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3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

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6

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Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

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