CVE-2021-35033Public exploit

Root access via hard-coded BusyBox password

Published Nov 23, 2021 · Updated Aug 4, 2024

Hard-coded credentials in Zyxel NBG6818, NBG7815, WSQ20, WSQ50, WSQ60, and WSR30 firmware allow attackers to gain root access. The firmware stores a non-user-configurable default password in /etc/uci_defconfig/system and accepts it for the root BusyBox shell exposed through the PCB UART port. Physical exploitation requires dismantling the device and attaching a USB-to-UART cable; network reachability requires an authenticated user to enable remote assistance.

CVSS severity7.8
High
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Hard-coded credentials in Zyxel NBG6818, NBG7815, WSQ20, WSQ50, WSQ60, and WSR30 firmware allow attackers to gain root access. The firmware stores a non-user-configurable default password in /etc/uci_defconfig/system and accepts it for the root BusyBox shell exposed through the PCB UART port. Physical exploitation requires dismantling the device and attaching a USB-to-UART cable; network reachability requires an authenticated user to enable remote assistance.

The record

CVE
CVE-2021-35033
Published
Nov 23, 2021
Updated
Aug 4, 2024
Vendor
Zyxel Networks
Product
Multy Mini Firmware (WSQ20)
Classifications
CWE-260, T1078.001
Attack vector
physical
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 23, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.00(ABOF.0)C0 through 1.00(ABOF.10)C0

What conditions does exploitation require?

Attack vectorphysical
Required privilegesunauthenticated

What is affected?

Zyxel Networks · Multy Mini Firmware (WSQ20)version=1.00(ABOF.0)C0 through 1.00(ABOF.10)C0
Zyxel Networks · Armor G5 Firmware (NBG7815)version=1.00(ABSK.0)C0 through 1.00(ABSK.6)C0
Zyxel Networks · Multy U Firmware (WSR30)version=1.00(ABMY.0)C0 through 1.00(ABMY.11)C0
Zyxel Networks · Armor G1 Firmware (NBG6818)version=1.00(ABSC.0)C0 through 1.00(ABSC.4)C0
Zyxel Networks · Multy X Firmware (WSQ50)version=1.00(ABKJ.0)C0 through 2.20(ABKJ.6)C0
Zyxel Networks · Multy Plus Firmware (WSQ60)version=1.00(ABND.0)C0 through 2.20(ABND.7)C0

Published CVSS scores

7.8ZyxelCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
7.8TenableCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorphysical
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-260Password in Configuration File
T1078.001Default Accounts

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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