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Vulnerability record · CVE-2021-35029 · published 2 July 2021

CVE-2021-35029: Zyxel usg1900 firmware improper authentication vulnerability

Zyxel · Usg1900 Firmware

An authentication bypasss vulnerability in the web-based management interface of Zyxel USG/Zywall series firmware versions 4.35 through 4.64 and USG Flex, ATP, and VPN series firmware versions 4.35 through 5.01, which could allow a remote attacker to execute arbitrary commands on an affected device.

9.8 CVSS 3.1 Critical EPSS 2.3% · top 17.7% CWE-287 · Improper authentication
9.8CVSS 3.1 base score, v2 7.5
2.3%EPSS exploitation probability, 30 days
NoNot in CISA KEV
37Affected product versions listed by NVD
2References
17 Jun 2026Last modified by NVD

Description

An authentication bypasss vulnerability in the web-based management interface of Zyxel USG/Zywall series firmware versions 4.35 through 4.64 and USG Flex, ATP, and VPN series firmware versions 4.35 through 5.01, which could allow a remote attacker to execute arbitrary commands on an affected device.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

37 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://www.zyxel.com/support/Zyxel_security_advisory_for_attacks_against_security_appliances.shtml Vendor Advisory
https://www.zyxel.com/support/Zyxel_security_advisory_for_attacks_against_security_appliances.shtml Vendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2023-33009Zyxel firewall notification function buffer overflowA buffer overflow in the notification function of multiple Zyxel firewall and VPN firmware lines (ATP, USG FLEX, USG20(W)-VPN, VPN, ZyWALL/USG) allow…KEVEPSS 28%analysed9.8CVE-2023-33010Zyxel firewall ID processing buffer overflow allows unauthenticated RCEA classic buffer overflow (CWE-120) exists in the ID processing function of multiple Zyxel firewall firmware lines, including ATP, USG FLEX, USG20(W)…KEVEPSS 29%analysed9.8CVE-2023-28771Zyxel firewall firmware OS command injection via crafted packetsZyxel ZyWALL/USG, VPN, USG FLEX and ATP series firmware mishandle error messages, allowing OS command injection. An unauthenticated remote attacker c…KEVEPSS 99%analysed9.8CVE-2022-30525Zyxel firewall CGI OS command injectionThe CGI program in multiple Zyxel firewall and VPN firmware lines fails to neutralize OS command syntax, allowing command injection. The flaw affects…KEVEPSS 100%analysed9.8CVE-2020-29583Zyxel USG and ATP firmware hard-coded admin credentialZyxel USG and ATP firmware version 4.60 ships an undocumented account (zyfwp) whose password is stored in cleartext in the firmware and cannot be cha…KEVEPSS 90%analysed9.8CVE-2022-0342Zyxel firewall CGI authentication bypass grants admin accessThe CGI program in multiple Zyxel firewall firmware lines (USG/ZyWALL, USG FLEX, ATP, VPN, NSG) fails to properly enforce authentication, allowing a …EPSS 95%analysed8.8CVE-2023-33011Zyxel usg 2200-vpn firmware vulnerabilityA format string vulnerability in the Zyxel ATP series firmware versions 5.10 through 5.36 Patch 2, USG FLEX series firmware versions 5.00 through 5.3…EPSS 0.34%8.8CVE-2023-33012Zyxel usg 20w-vpn firmware os command injection vulnerabilityA command injection vulnerability in the configuration parser of the Zyxel ATP series firmware versions 5.10 through 5.36 Patch 2, USG FLEX series fi…EPSS 9.9%

Source: NIST National Vulnerability Database (record CVE-2021-35029), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.