CVE-2026-7273: Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability

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.

What to do

Schedule the vendor fix into this week’s change window, prioritising internet-facing and business-critical systems. Confirm the fix is applied everywhere, not just where it was easy.

Priority

This week: Schedule into this week’s change window.

Severity (CVSS)

8.8 high

CISA assessment (SSVC)

actively exploited; needs manual effort per target; total control of the affected system

Exploit probability (EPSS, 30 days)

2.5%, higher than 84% of all CVEs

Added to CISA KEV

21 September 2026

CISA fix-by date

24 September 2026 (US federal agencies; a sensible deadline for everyone)

Ransomware use

Not known

Weakness

CWE-121

References

• NIST NVD entry
• CISA KEV entry
• www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-
• www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-7273
• www.greynoise.io/blog/open-season-on-kapibala-attacker-steals-government-records

Sources: CISA Known Exploited Vulnerabilities · FIRST Exploit Prediction Scoring System (EPSS) · NIST National Vulnerability Database · CISA Vulnrichment (SSVC), via the CVE Program. This product uses data from the NVD API but is not endorsed or certified by the NVD. Summaries are machine-written from CISA’s description; treat the vendor’s advisory as the authority for fixes.