An authentication bypasss vulnerability in the web-based management interface of Zyxel USG/Zywall series firmware versions 4.35 through 4.6…

published 2021-07-02 5y ago modified 2026-06-17 4mo ago also EUVD-2021-21676

cvss: 9.8; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 2.3%; EPSS 2.3% chance of exploitation in 30 days, percentile 83%
public exploits: 0; none known

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.

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Exploit prediction

2.26% chance of exploitation in the next 30 days, higher than 83% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by	version	score	vector
CNA	3.1	9.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD	3.1	9.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD	2.0	7.5	AV:N/AC:L/Au:N/C:P/I:P/A:P

Affected products

Zyxel USG/Zywall series Firmware
Zyxel USG FLEX series Firmware
Zyxel ATP series Firmware
Zyxel VPN series Firmware

Classification

Weakness

CWE-287 Improper Authentication

References

zyxel.com /support/Zyxel_security_advisory_for_attacks_against_security_appliances.shtml
vendor-advisory

Sources

CVE List CVE-2021-35029
NVD CVE-2021-35029

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