CVE-2020-9054: Multiple ZyXEL network-attached storage (NAS) devices running firmware version 5.21 contain a pre-authentication command injection vulnerability, whic...

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

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

99.99%

100.0th percentile

Probability of exploitation in the next 30 days. Learn more

Exploitation Status

This vulnerability is listed in CISA’s Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild. Federal agencies must remediate by Apr 15, 2022.

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Zyxel	Nas326 Firmware	< 5.21\(aazf.7\)c0
Zyxel	Nas520 Firmware	< 5.21\(aasz.3\)c0
Zyxel	Nas540 Firmware	< 5.21\(aatb.4\)c0
Zyxel	Nas542 Firmware	< 5.21\(abag.4\)c0
Zyxel	Atp100 Firmware	>= 4.35, < 4.35\(abps.3\)c0
Zyxel	Atp200 Firmware	>= 4.35, < 4.35\(abfw.3\)c0
Zyxel	Atp500 Firmware	>= 4.35, < 4.35\(abfu.3\)c0
Zyxel	Atp800 Firmware	>= 4.35, < 4.35\(abiq.3\)c0
Zyxel	Usg20-Vpn Firmware	>= 4.35, < 4.35\(abaq.3\)c0
Zyxel	Usg20w-Vpn Firmware	>= 4.35, < 4.35\(abar.3\)c0
Zyxel	Usg40 Firmware	>= 4.35, < 4.35\(aala.3\)c0
Zyxel	Usg40w Firmware	>= 4.35, < 4.35\(aalb.3\)c0
Zyxel	Usg60 Firmware	>= 4.35, < 4.35\(aaky.3\)c0
Zyxel	Usg60w Firmware	>= 4.35, < 4.35\(aakz.3\)c0
Zyxel	Usg110 Firmware	>= 4.35, < 4.35\(aaph.3\)c0
Zyxel	Usg210 Firmware	>= 4.35, < 4.35\(aapi.3\)c0
Zyxel	Usg310 Firmware	>= 4.35, < 4.35\(aapj.3\)c0
Zyxel	Usg1100 Firmware	>= 4.35, < 4.35\(aapk.3\)c0
Zyxel	Usg1900 Firmware	>= 4.35, < 4.35\(aapl.3\)c0
Zyxel	Usg2200 Firmware	>= 4.35, < 4.35\(abae.3\)c0
Zyxel	Vpn50 Firmware	>= 4.35, < 4.35\(abhl.3\)c0
Zyxel	Vpn100 Firmware	>= 4.35, < 4.35\(abfv.3\)c0
Zyxel	Vpn300 Firmware	>= 4.35, < 4.35\(abfc.3\)c0
Zyxel	Vpn1000 Firmware	>= 4.35, < 4.35\(abip.3\)c0
Zyxel	Zywall110 Firmware	>= 4.35, < 4.35\(aaaa.3\)c0
Zyxel	Zywall310 Firmware	>= 4.35, < 4.35\(aaab.3\)c0
Zyxel	Zywall1100 Firmware	>= 4.35, < 4.35\(aaac.3\)c0

References

https://cwe.mitre.org/data/definitions/78.htmlThird Party Advisory
https://kb.cert.org/artifacts/cve-2020-9054.htmlThird Party Advisory, US Government Resource
https://kb.cert.org/vuls/id/498544/Third Party Advisory, US Government Resource
https://krebsonsecurity.com/2020/02/zyxel-fixes-0day-in-network-storage-devices/Exploit, Third Party Advisory
https://www.zyxel.com/support/remote-code-execution-vulnerability-of-NAS-products.shtmlVendor Advisory
https://cwe.mitre.org/data/definitions/78.htmlThird Party Advisory
https://kb.cert.org/artifacts/cve-2020-9054.htmlThird Party Advisory, US Government Resource
https://kb.cert.org/vuls/id/498544/Third Party Advisory, US Government Resource
https://krebsonsecurity.com/2020/02/zyxel-fixes-0day-in-network-storage-devices/Exploit, Third Party Advisory
https://www.zyxel.com/support/remote-code-execution-vulnerability-of-NAS-products.shtmlVendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-9054US Government Resource

Timeline

Published: Mar 4, 2020
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2020-9054?

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

How severe is CVE-2020-9054?

CVE-2020-9054 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 99.99% probability of exploitation in the next 30 days. This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog.

How do I fix CVE-2020-9054?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.