CISA KEV catalog
Confirmed active exploitation.
Listed in CISA's catalog of Known Exploited Vulnerabilities: attackers are using it in real attacks. Patch it with priority.
- Name
- Zyxel Multiple Firewalls OS Command Injection Vulnerability
- Added to catalog
- Remediation due date (US federal)
- Required action
- Apply updates per vendor instructions.
Description
A OS command injection vulnerability in the CGI program of Zyxel USG FLEX 100(W) firmware versions 5.00 through 5.21 Patch 1, USG FLEX 200 firmware versions 5.00 through 5.21 Patch 1, USG FLEX 500 firmware versions 5.00 through 5.21 Patch 1, USG FLEX 700 firmware versions 5.00 through 5.21 Patch 1, USG FLEX 50(W) firmware versions 5.10 through 5.21 Patch 1, USG20(W)-VPN firmware versions 5.10 through 5.21 Patch 1, ATP series firmware versions 5.10 through 5.21 Patch 1, VPN series firmware versions 4.60 through 5.21 Patch 1, which could allow an attacker to modify specific files and then execute some OS commands on a vulnerable device.
Affected products
zyxel: usg flex 100w firmware; zyxel: usg flex 100w; zyxel: usg flex 200 firmware; zyxel: usg flex 200; zyxel: usg flex 500 firmware; zyxel: usg flex 500; zyxel: usg flex 700 firmware; zyxel: usg flex 700; zyxel: vpn100 firmware; zyxel: vpn100; zyxel: vpn1000 firmware; zyxel: vpn1000; zyxel: vpn300 firmware; zyxel: vpn300; zyxel: vpn50 firmware
References10
- www.zyxel.com/support/Zyxel-security-advisory-for-OS-command-in… Vendor Advisory
- www.zyxel.com/support/Zyxel-security-advisory-for-OS-command-in… Vendor Advisory
- packetstormsecurity.com/files/167182/Zyxel-Firewall-ZTP-Unauthe… ExploitThird Party AdvisoryVDB Entry
- packetstormsecurity.com/files/167372/Zyxel-USG-FLEX-5.21-Comman… ExploitThird Party AdvisoryVDB Entry
- packetstormsecurity.com/files/168202/Zyxel-Firewall-SUID-Binary… ExploitThird Party Advisory
- packetstormsecurity.com/files/167182/Zyxel-Firewall-ZTP-Unauthe… ExploitThird Party AdvisoryVDB Entry
- packetstormsecurity.com/files/167372/Zyxel-USG-FLEX-5.21-Comman… ExploitThird Party AdvisoryVDB Entry
- packetstormsecurity.com/files/168202/Zyxel-Firewall-SUID-Binary… ExploitThird Party Advisory
- packetstormsecurity.com/files/167176/Zyxel-Remote-Command-Execu… Third Party AdvisoryVDB Entry
- packetstormsecurity.com/files/167176/Zyxel-Remote-Command-Execu… Third Party AdvisoryVDB Entry
Metrics
- CVSS 3.1
-
9.8
CRITICAL
Score source: NVD
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H - EPSS — exploit probability
- 100% percentile: 100 · as of 2 November 2026
- CWE
- CWE-78