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CVE-2026-18588 – Unauthenticated Stack-Based Buffer Overflow (RCE) – WAVLINK WL-NU516U1 firmware 708

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Summary

CVE-2026-18588 is a stack-based buffer overflow (CWE-121 / CWE-119) in the WAVLINK WL-NU516U1 router web interface, affecting firmware build 708c073-mt7628. The flaw resides in the fgets handling within nas.cgi and can be triggered remotely without authentication, resulting in memory corruption and potential remote code execution. It is rated CRITICAL (CVSS v4.0 9.3, CVSS v3.1 9.8).

Technical details

  • Root cause: Improper handling of the CONTENT_LENGTH argument in the fgets function of the nas.cgi file leads to a stack-based buffer overflow.
  • Trigger conditions: An attacker manipulates the CONTENT_LENGTH value in a request to the vulnerable component; no authentication or user interaction is required.
  • Attack vector: Network (remote). The exploit is reachable over the device’s web interface.
  • Impact: Memory corruption on the stack, enabling denial of service and potential arbitrary code execution with full compromise of confidentiality, integrity, and availability.

Affected software

  • WAVLINK WL-NU516U1, firmware build 708c073-mt7628 (2026-05-15).

Severity

  • CVSS v3.1: 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: 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: WAVLINK was notified and released a fixed firmware image (build dated 2026-07-13, 4b8a21f-mt7628). Upgrade affected WL-NU516U1 devices to the latest vendor firmware.
  • If no patch can be applied yet: Restrict access to the router’s web management interface. Ensure the device is not exposed to the internet, and limit administrative access to trusted management networks or VLANs. Disable remote/WAN-side management if enabled.

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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1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

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.

5

Execute Exploit Validations

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

Drive Fast and Actionable Remediation

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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