CVE-2021-35029

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.

Published: 2021-07-02 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-35029 is rated Moderate Risk (53.1/100): CVSS Critical severity, with low exploitation likelihood (EPSS 0.20%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-35029

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-17 0.71% 0.20% -0.52%
2 2025-11-21 0.80% 0.71% -0.09%
3 2025-11-18 — 0.80% —

Full EPSS history (15 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-35029

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-35029

Affected software / configurations for CVE-2021-35029

Vendor Product Version Raw CPE
zyxel usg1900_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg1900_firmware:*:*:*:*:*:*:*:*
zyxel usg1100_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg1100_firmware:*:*:*:*:*:*:*:*
zyxel usg310_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg310_firmware:*:*:*:*:*:*:*:*
zyxel usg210_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg210_firmware:*:*:*:*:*:*:*:*
zyxel usg110_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg110_firmware:*:*:*:*:*:*:*:*
zyxel usg40_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg40_firmware:*:*:*:*:*:*:*:*
zyxel usg40w_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg40w_firmware:*:*:*:*:*:*:*:*
zyxel usg60_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg60_firmware:*:*:*:*:*:*:*:*
zyxel usg60w_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg60w_firmware:*:*:*:*:*:*:*:*
zyxel usg300_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg300_firmware:*:*:*:*:*:*:*:*
zyxel usg1000_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg1000_firmware:*:*:*:*:*:*:*:*
zyxel usg2000_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg2000_firmware:*:*:*:*:*:*:*:*
zyxel usg20_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg20_firmware:*:*:*:*:*:*:*:*
zyxel usg20w_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg20w_firmware:*:*:*:*:*:*:*:*
zyxel usg50_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg50_firmware:*:*:*:*:*:*:*:*
zyxel usg100_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg100_firmware:*:*:*:*:*:*:*:*
zyxel usg200_firmware >= 4.35, <= 4.64 cpe:2.3:o:zyxel:usg200_firmware:*:*:*:*:*:*:*:*
zyxel usg_flex_100_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:usg_flex_100_firmware:*:*:*:*:*:*:*:*
zyxel usg_flex_200_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:usg_flex_200_firmware:*:*:*:*:*:*:*:*
zyxel usg_flex_500_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:usg_flex_500_firmware:*:*:*:*:*:*:*:*
zyxel usg_flex_100w_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:usg_flex_100w_firmware:*:*:*:*:*:*:*:*
zyxel usg_flex_700_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:usg_flex_700_firmware:*:*:*:*:*:*:*:*
zyxel zywall_atp100_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:zywall_atp100_firmware:*:*:*:*:*:*:*:*
zyxel zywall_atp100w_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:zywall_atp100w_firmware:*:*:*:*:*:*:*:*
zyxel zywall_atp200_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:zywall_atp200_firmware:*:*:*:*:*:*:*:*
zyxel zywall_atp500_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:zywall_atp500_firmware:*:*:*:*:*:*:*:*
zyxel zywall_atp700_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:zywall_atp700_firmware:*:*:*:*:*:*:*:*
zyxel zywall_atp800_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:zywall_atp800_firmware:*:*:*:*:*:*:*:*
zyxel zywall_vpn50_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:zywall_vpn50_firmware:*:*:*:*:*:*:*:*
zyxel zywall_vpn100_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:zywall_vpn100_firmware:*:*:*:*:*:*:*:*
zyxel zywall_vpn300_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:zywall_vpn300_firmware:*:*:*:*:*:*:*:*
zyxel usg20-vpn_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:usg20-vpn_firmware:*:*:*:*:*:*:*:*
zyxel usg20w-vpn_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:usg20w-vpn_firmware:*:*:*:*:*:*:*:*
zyxel usg2200-vpn_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:usg2200-vpn_firmware:*:*:*:*:*:*:*:*
zyxel zywall_110_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:zywall_110_firmware:*:*:*:*:*:*:*:*
zyxel zywall_310_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:zywall_310_firmware:*:*:*:*:*:*:*:*
zyxel zywall_1100_firmware >= 4.35, <= 5.01 cpe:2.3:o:zyxel:zywall_1100_firmware:*:*:*:*:*:*:*:*

References for CVE-2021-35029

cvelogic Threat Intelligence