Zyxel · Multiple Network-Attached Storage (NAS) Devices
CVE-2020-9054
ZyXEL NAS products running firmware version 5.21 and earlier are vulnerable to pre-authentication command injection in weblogin.cgi
What it is
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
CISA: Multiple Zyxel network-attached storage (NAS) devices contain a pre-authentication command injection vulnerability, which may allow a remote, unauthenticated attacker to execute arbitrary code.
What to do
Apply updates per vendor instructions.
Deadline for US federal agencies: April 15, 2022
- Added to the CISA list
- March 25, 2022
- Published
- March 4, 2020
- Severity
- Critical 9.8 CVSS 3.1
- Chance of attacks in the next 30 days (EPSS)
- >99.9% in the top 0.1% of all known vulnerabilities
- Weakness
- CWE-78
- More details
- NVD · CVE.org · CISA
All references (5)
More exploited flaws from Zyxel
| Added | Vulnerability | Product | Severity | Attack chance |
|---|---|---|---|---|
| Jun 23, 2023 | Multiple NAS Devices Command Injection | Multiple Network-Attached Storage (NAS) Devices | Critical 9.8 | 82% |
| Sep 21, 2026 | Stack-Based Buffer Overflow | GS1900 Series Switches | High 8.8 | 2.8% |
| Feb 11, 2025 | DSL CPE OS Command Injection | DSL CPE Devices | High 8.8 | 21% |
| Feb 11, 2025 | DSL CPE OS Command Injection | DSL CPE Devices | High 8.8 | 23% |
| Dec 3, 2024 | Path Traversal | Multiple Firewalls | High 7.5 | 2.9% |
| Sep 18, 2023 | Command Injection | EMG2926 Routers | High 8.8 | 33% |
| Aug 7, 2023 | Command Injection | P660HN-T1A Routers | Critical 9.8 | 95% |
| Jun 5, 2023 | Buffer Overflow | Multiple Firewalls | Critical 9.8 | 28% |
Sources: Known Exploited Vulnerabilities (CISA, public domain), CVE records (cve.org) and EPSS (FIRST). The chance of attacks is the EPSS estimate that someone will try to exploit the flaw in the next 30 days.