Exploited. On CISA's list since 2026-09-21.

Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability

CVE-2026-7273 · Zyxel GS1900 Series Switches · Published 2026-06-16

How bad would it be?

8.8 out of 10

CVSS rates it high.

How likely is it to be used?

2.8%

Estimated chance of exploitation in the next 30 days, higher than 86% of all scored flaws (EPSS, 2026-10-29).

Is it already being used?

Yes

CISA has seen it exploited in real attacks. For US government agencies the fix is deadline passed 36 days ago (2026-09-24).

What CISA says to do

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

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 the flaw is

A stack-based buffer overflow vulnerability in the CGI program of Zyxel GS1900-48HPv2 firmware versions through 2.90(ABTQ.1)C0 could allow a LAN-based, unauthenticated attacker to exploit the flaw and potentially execute OS commands via a crafted HTTP request.

From the NVD.

Fixes and advisories

www.zyxel.comVendor Advisory

Learn this

Explore this week’s weaknesses and all learning topics

Understand the kind of weakness behind this flaw. These resources teach the weakness, rather than reproduce this specific CVE. Follow the vendor's advice above to fix the affected product.

Stack buffer overflow

A write runs past a buffer on the stack and can overwrite nearby program state.

CWE-121 · CISA KEV; NVD record: security@zyxel.com.tw

Video course · Free course. C programming and memory concepts are useful; covers several weakness types.

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CWE is a catalogue of weakness types. Labels come from the sources shown and can differ or change. Resource matches reviewed 16 October 2026.

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Exploited flaws from CISA's KEV catalogue. Chance of exploitation from EPSS by FIRST. Descriptions and scores from the NVD. This product uses the NVD API but is not endorsed or certified by the NVD.