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CVE-2026-18589 – Unauthenticated Stack-Based Buffer Overflow (RCE) – WAVLINK WL-NU516U1 firmware 708

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Summary

CVE-2026-18589 is an unauthenticated stack-based buffer overflow in the WAVLINK WL-NU516U1 router web interface. The flaw resides in the change_password function of nas.cgi, where the User1Passwd argument is copied without bounds checking, corrupting stack memory and potentially allowing remote code execution. It affects firmware version 708c073-mt7628 and is rated Critical.

Technical details

  • Root cause: The change_password function in nas.cgi copies the attacker-supplied User1Passwd parameter into a fixed-size stack buffer without validating its length (CWE-121 / CWE-119).
  • Trigger conditions: Sending an overly long User1Passwd value to the vulnerable nas.cgi handler overflows the stack buffer.
  • Attack vector: Network — remotely exploitable over the router’s web management interface with no authentication and no user interaction required.
  • Impact: Stack memory corruption leading to a potential loss of confidentiality, integrity, and availability, including possible remote code execution on the device.

Affected software

  • WAVLINK WL-NU516U1, firmware version 708c073-mt7628.

Severity

  • CVSS v3.1 base score: 9.8 (Critical) — CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • CVSS v4.0 base score: 9.3 (Critical) — CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Update to the fixed WAVLINK firmware for the WL-NU516U1 (WINSTAR_NU516U1-WO-A build 4b8a21f-mt7628, dated 2026-07-13) available from the WAVLINK firmware download portal.
  • If no patch can be applied: Restrict access to the router’s web management interface. Do not expose the management UI to the internet, limit administration to trusted LAN hosts, and place the device behind a firewall or ACL that blocks external access to nas.cgi.

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: WAVLINK, WAVLINK Router, WAVLINK Mesh Router, WAVLINK WiFi Router
  • Raw response body: WAVLINK, Login, Login Now, Device Management, Mesh Router, Device management password, wavlogin.link, wifi.wavlink.com, waplogin.link

References

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Map your entire attack surface (continously)

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4

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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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By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

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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