Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability

🚨SEVERITY: HIGH — CVSS 8.8Security Advisory

TL;DR 📌

  • Zyxel GS1900 series switches contain a stack-based buffer overflow vulnerability in the CGI program which could allow a LAN-based, unauthenticated attacker to exploit the flaw and potentially execute OS commands via a crafted HTTP request.
  • Highest CVSS: 8.8 (High).
  • Listed in CISA KEV (2026-09-21) — this is being exploited in the wild.
  • Fixed in 2.90\(aahh.2\)c0, 2.90\(aahi.2\)c0, 2.90\(aahj.2\)c0, 2.90\(aahk.2\)c0 — upgrade to this release or later.
  • CVEs: CVE-2026-7273.

What it is

Zyxel GS1900 series switches contain a stack-based buffer overflow vulnerability in the CGI program which could allow a LAN-based, unauthenticated attacker to exploit the flaw and potentially execute OS commands via a crafted HTTP request.

For leadership 🧭

Executive summary. Risk is High (CVSS 8.8) across any Zyxel kit you run. Follow the remediation in the vendor advisory within Immediate — CISA KEV entries carry a federal remediation deadline.

Why it matters:

  • Exposure depends on deployment topology and which access paths reach the affected component.
  • Treat internet-facing and management-plane instances as higher risk than internal-only ones.
  • Keep monitoring for abnormal authentication and configuration events until upgrades complete.

Now / Next / Later:

  • Now: confirm whether you run the affected versions, and check exposure of any that are internet-facing.
  • Next: apply the remediation the advisory specifies, through an approved change window.
  • Later: add a control check so builds cannot drift back onto a vulnerable train.

Source