CVE-2026-7273

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.

What this means for your business

It affects Zyxel GS1900 Series Switches. It matters if your company, or a supplier that handles your data, runs it.
Attackers are already using it. CISA added it to its list of flaws used in real attacks on 21 September 2026.
An attacker can use it from inside the same network, without a login, and without anyone at your company clicking anything.
FIRST's prediction model gives it a 0.3% chance of attack attempts being seen in the next 30 days, ranking above 24% of all known flaws.

What to do

1Check whether your company or your suppliers run Zyxel GS1900 Series Switches.
2If you do, follow CISA's required action below. No patch reference has been published yet.
3Treat it as urgent. US federal agencies must fix it by 24 September 2026. That deadline does not apply to private companies, but it shows how seriously CISA takes it.
4Because attackers have used it, check the affected systems for signs of a break-in, not only for the update.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

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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.

CISA’s wording, unedited. The notes it mentions are in CISA’s catalogue entry.

Scoring

CVSS: 8.8 (v3.1)
Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness: CWE-121
Assigned by: security@zyxel.com.tw

Dates

Published: 2026-06-16
Last modified: 2026-09-22
Added to KEV: 2026-09-21
Remediation due: 2026-09-24
Sources: CISA KEV, NVD

Coverage

Zyxel and Veeam Flaws Under Active Exploitation With Command and SYSTEM AccessThe Hacker News · 2026-09-22