CVE-2026-7273
CVE-2026-7273 is a security flaw in Zyxel GS1900 Series Switches, firewalls and routers for homes and small businesses. Attackers can run commands on Zyxel GS1900 Series Switches from anywhere, without logging in. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 21 Sep 2026.[1]
Zyxel GS1900 Series Switches is in things households have: home and small-office routers, so the fix matters at home as much as at work. Zyxel has published a fix or advice.
Description
CISA calls it a stack-based buffer overflow in Zyxel GS1900 Series Switches. In its words: “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.”[1]
The underlying weakness is stack buffer overflow (CWE-121), in MITRE’s list of common software weaknesses.[2]
It scores 8.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by the organisation that published the CVE using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Zyxel’s advisory has them[3]. CISA names the product as Zyxel GS1900 Series Switches.
Every device with Zyxel GS1900 Series Switches needs the update.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 21 Sep 2026, 97 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 24 Sep 2026 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 3%. That’s in the top 14% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Zyxel has published a fix or advice.[3] CISA’s 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).”[1]
- Update Zyxel GS1900 Series Switches now.Open the router’s app, or its admin page in a browser, and look for a firmware update. Then turn on automatic updates, so the next fix arrives on its own.
- If the maker has stopped updating it, replace it.Routers stop getting fixes after a few years, and attackers keep a list of the ones that did. If there’s no newer firmware, it won’t be fixed.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 8.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 3%.[4] |
See also
Other Zyxel flaws
- CVE-2024-40891, Zyxel DSL CPE Devices: DSL CPE OS command injection ·
- CVE-2024-40890, Zyxel DSL CPE Devices: DSL CPE OS command injection ·
- CVE-2024-11667, Zyxel Multiple Firewalls: path traversal ·
- CVE-2017-6884, Zyxel EMG2926 Routers: command injection ·
- CVE-2017-18368, Zyxel P660HN-T1A Routers: command injection ·
Other stack buffer overflow flaws
- CVE-2021-27137, DD-WRT: stack-based buffer overflow ·
- CVE-2025-53521, F5 BIG-IP: stack-based buffer overflow ·
- CVE-2025-20352, Cisco IOS and IOS XE: software SNMP denial of service and remote code execution ·
- CVE-2025-42599, Qualitia Active! Mail: stack-based buffer overflow ·
- CVE-2025-22457, Ivanti Connect Secure, Policy Secure, and ZTA Gateways: stack-based buffer overflow ·
Every Zyxel flaw on CISA’s list · Everything added in September 2026
References
- ^ Cybersecurity and Infrastructure Security Agency. “Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability”. Known Exploited Vulnerabilities Catalog, added 21 Sep 2026.
- ^ National Institute of Standards and Technology. “CVE-2026-7273 Detail”. National Vulnerability Database, published 16 Jun 2026.
- ^ Zyxel. Advisories and fixes: zyxel.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.028, percentile 86.4, 31 Oct 2026.
- CVE Program. “CVE-2026-7273”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.