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CVE-2026-15579 – Unauthenticated Denial of Service via Buffer Overflow – Moxa TN-4500B Series Ethern

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Summary

CVE-2026-15579 is an out-of-bounds write vulnerability affecting the Moxa TN-4500B Series of Ethernet switches. The flaw is caused by improper validation of the username field length during the web login process, allowing a remote, unauthenticated attacker to crash the device’s authentication service. Moxa rates the issue as HIGH severity (CVSS 8.8) and has released a fixed firmware version.

Technical details

  • Root cause: The web-based login handler on affected Ethernet switches does not properly validate the length of the submitted username field before writing it into memory.
  • Trigger condition: An attacker submits a specially crafted, overly long username value to the device’s web login interface.
  • Attack vector: Network — the login page is reachable over the network without any prior authentication or user interaction.
  • Impact: The out-of-bounds write corrupts memory used by the authentication process, causing it to crash. This results in a Denial of Service (DoS), disrupting management access and/or normal switch operation.

Affected software

  • Moxa TN-4500B Series — firmware versions 1.0 through 2.0 (inclusive)
  • Fixed in firmware version 2.1 and later

Severity

  • CVSS Score: 8.8 (High)
  • CVSS v4.0 Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N
  • Network attack vector, low attack complexity, no privileges or user interaction required, with high impact on availability.

Mitigation and recommended actions

  • Immediate: Upgrade affected Moxa TN-4500B Series switches to firmware version 2.1 or later.
  • If immediate patching is not possible:
    • Restrict network access to the switch’s web management interface using firewalls or access control lists, limiting it to trusted management IP ranges.
    • Avoid exposing the switch’s web login interface directly to the internet.
    • Disable unnecessary services on the device and enforce strong authentication and password policies where applicable.
    • Monitor network traffic and device logs for repeated or malformed login attempts, and maintain audit logs for forensic review.
    • Periodically reassess the device against Moxa’s published security advisories for further guidance.

References

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