CVE-2026-7273

Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability

Actively exploited (CISA KEV) High 8.8 CVSS 3.1

Description

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.

Description as published by the source, in English.

Key facts

Published: 2026-06-16
Last modified: 2026-09-22
Assigned by: security@zyxel.com.tw
CVSS vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Scored by: security@zyxel.com.tw
Probability of exploitation: 0.3 % higher than 24 % of all known vulnerabilities
EPSS, next 30 days, model v2026.06.15
Fix available: Not registered in the sources

Actively exploited

CISA added this vulnerability to the Known Exploited Vulnerabilities catalogue on 2026-09-21, with a remediation deadline of 2026-09-24 for US federal agencies.

Required action: 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.

Affected products

Vendor	Product	Versions	Status
Zyxel	Gs1900-10hp	all versions listed	Not affected
Zyxel	Gs1900-10hp Firmware	< 2.90\(aazi.2\)c0	Affected
Zyxel	Gs1900-16	all versions listed	Not affected
Zyxel	Gs1900-16 Firmware	< 2.90\(aahj.2\)c0	Affected
Zyxel	Gs1900-24	all versions listed	Not affected
Zyxel	Gs1900-24 Firmware	< 2.90\(aahl.2\)c0	Affected
Zyxel	Gs1900-24e	all versions listed	Not affected
Zyxel	Gs1900-24e Firmware	< 2.90\(aahk.2\)c0	Affected
Zyxel	Gs1900-24ep	all versions listed	Not affected
Zyxel	Gs1900-24ep Firmware	< 2.90\(abto.2\)c0	Affected
Zyxel	Gs1900-24hpv2	all versions listed	Not affected
Zyxel	Gs1900-24hpv2 Firmware	< 2.90\(abtp.2\)c0	Affected
Zyxel	Gs1900-48	all versions listed	Not affected
Zyxel	Gs1900-48 Firmware	< 2.90\(aahn.2\)c0	Affected
Zyxel	Gs1900-48hpv2	all versions listed	Not affected
Zyxel	Gs1900-48hpv2 Firmware	< 2.90\(abtq.2\)c0	Affected
Zyxel	Gs1900-8	all versions listed	Not affected
Zyxel	Gs1900-8 Firmware	< 2.90\(aahh.2\)c0	Affected
Zyxel	Gs1900-8hp	all versions listed	Not affected
Zyxel	Gs1900-8hp Firmware	< 2.90\(aahi.2\)c0	Affected

Weakness type

CWE-121: Stack-based Buffer Overflow
A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

References

https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-s… Vendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-7273 Third Party Advisory, US Government Resource
https://www.greynoise.io/blog/open-season-on-kapibala-attacker-steals-government-records-… Exploit, Third Party Advisory

Related at Berigo

Articles

Zyxel fixes buffer overflow in GS1900 switches Mentions this CVE 2026-06-16
CVE-2026-7273 lets an unauthenticated attacker on the LAN run OS commands on Zyxel GS1900 switches.

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The order that decides what is urgent

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A short example

Fix this week

CVSS 6,5 (medium)

In CISA KEV: yes
EPSS: 94 per cent
A firewall facing the internet

Can be scheduled

CVSS 9,8 (critical)

In CISA KEV: no
EPSS: 0,04 per cent
A test server with no internet access

Sorted by CVSS alone, the one on the right comes first. It is the more serious flaw in theory. But the one on the left is being used against real organisations right now, and it sits where an attacker can reach it. That is the one to fix first.

The critical one still has to be fixed. It just does not have to be fixed today.

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