Vulnerability Intelligence

CVE-2020-9054

Critical 9.8 Exploited in the wild (KEV)

Published
Last modified
NVD status
Analyzed

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.

CISA KEV
Name
Zyxel Multiple NAS Devices OS Command Injection Vulnerability
Added to catalog
Remediation due date (US federal)
Required action
Apply updates per vendor instructions.

Description

Multiple ZyXEL network-attached storage (NAS) devices running firmware version 5.21 contain a pre-authentication command injection vulnerability, which may allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable device. ZyXEL NAS devices achieve authentication by using the weblogin.cgi CGI executable. This program fails to properly sanitize the username parameter that is passed to it. If the username parameter contains certain characters, it can allow command injection with the privileges of the web server that runs on the ZyXEL device. Although the web server does not run as the root user, ZyXEL devices include a setuid utility that can be leveraged to run any command with root privileges. As such, it should be assumed that exploitation of this vulnerability can lead to remote code execution with root privileges. By sending a specially-crafted HTTP POST or GET request to a vulnerable ZyXEL device, a remote, unauthenticated attacker may be able to execute arbitrary code on the device. This may happen by directly connecting to a device if it is directly exposed to an attacker. However, there are ways to trigger such crafted requests even if an attacker does not have direct connectivity to a vulnerable devices. For example, simply visiting a website can result in the compromise of any ZyXEL device that is reachable from the client system. Affected products include: NAS326 before firmware V5.21(AAZF.7)C0 NAS520 before firmware V5.21(AASZ.3)C0 NAS540 before firmware V5.21(AATB.4)C0 NAS542 before firmware V5.21(ABAG.4)C0 ZyXEL has made firmware updates available for NAS326, NAS520, NAS540, and NAS542 devices. Affected models that are end-of-support: NSA210, NSA220, NSA220+, NSA221, NSA310, NSA310S, NSA320, NSA320S, NSA325 and NSA325v2

Affected products

zyxel: nas326 firmware; zyxel: nas326; zyxel: nas520 firmware; zyxel: nas520; zyxel: nas540 firmware; zyxel: nas540; zyxel: nas542 firmware; zyxel: nas542; zyxel: atp100 firmware; zyxel: atp100; zyxel: atp200 firmware; zyxel: atp200; zyxel: atp500 firmware; zyxel: atp500; zyxel: atp800 firmware

References10

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 11 November 2026
CWE
CWE-78

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