Zyxel GS1900 Series Switches: a memory flaw attackers can abuse
OFFICIAL NAME: Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability
WHAT IT IS · ROUTERS, CAMERAS AND DEVICESRouters, cameras and recorders are often forgotten and rarely updated.
DO THIS FIRSTUpdate it or replace it. Never leave its admin page open to the internet. Not sure if you use it? Send this page to your IT provider or security lead and ask.
TECHNICAL SUMMARY 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.
WHY THIS VERDICT Attacks are confirmed. The vulnerability is 148 days old, so many systems are likely still unpatched.
WHY IT RANKS HERE Exploitation is confirmed by an authoritative source. 11 products are affected.
- HIGHEST CONFIRMED RUNG
- EXPLOITED
- CISA KEV
- LISTED
- EXPLOIT CODE
- NONE KNOWN
How far has it climbed?
01 TALK
■ CONFIRMEDNEWEST EVIDENCE · 2 INDEPENDENT SOURCESCVE-2026-7273 discussed publicly (CIRCL sighting). CVE-2026-7273 discussed publicly (CIRCL sighting).
02 EXPOSED
□ NOT TRACKED YETNO SOURCE FOR THIS STEP YETWe have no source that counts exposed systems yet. Internet scan data needs a partnership we do not have. No evidence here does not mean nothing is exposed.
03 TRIED
■ CONFIRMEDNEWEST EVIDENCE · 2 INDEPENDENT SOURCESAttacks that worked are confirmed (step 4), so attempts count as confirmed too.
04 EXPLOITED
■ CONFIRMEDNEWEST EVIDENCE · 2 INDEPENDENT SOURCESZyxel 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. CISA Vulnrichment marks CVE-2026-7273 as actively exploited.
05 DAMAGE
□ NOT TRACKED YETNO SOURCE FOR THIS STEP YETBreach notices and filings rarely name the flaw that was used, so we cannot link them to this event yet. No evidence here does not mean no harm.
When each thing happened
- DISCLOSED
- EXPLOIT CODE PUBLICNOT YET
- FIRST ATTACK REPORT
- CISA KEV LISTING
- US FEDERAL DEADLINE
THE FIX
CISA's instruction: apply the vendor's fix, or stop using the product if no fix exists. The deadline CISA set for US federal agencies, Sep 24, 2026, has passed. It is a US government deadline; use it as a guide.
Questions to ask this week
- Do we run Zyxel GS1900 Series Switches? If yes, is it patched or cut off from the internet?
- Who owns fixing it, and by what date?
- Have we checked for signs of attack since the first report, not just since the patch?
How it unfolded
- Attack activity. JUN 15, 2026CISA Vulnrichment marks CVE-2026-7273 as actively exploited
- Attack activity. SEP 20, 2026Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability
- NOV 3, 2026CVE-2026-7273 discussed publicly (CIRCL sighting) (12 reports, latest NOV 9)
- NOV 5, 2026Patched Zyxel GS1900 switches remained open to in-the-wild exploit (CVE-2026-107441)
SOURCES
- [1] CIRCL Vulnerability-Lookup sightings: CVE-2026-7273 discussed publicly (CIRCL sighting), NOV 9
- [2] Help Net Security: Patched Zyxel GS1900 switches remained open to in-the-wild exploit (CVE-2026-107441), NOV 5
- [3] CISA Known Exploited Vulnerabilities: Zyxel GS1900 Series Switches Stack-Based Buffer Overflow Vulnerability, SEP 20
- [4] CVE List V5 and CISA Vulnrichment: CISA Vulnrichment marks CVE-2026-7273 as actively exploited, JUN 15
- [5] CIRCL Vulnerability-Lookup sightings: 11 more reports