CVE-2020-9054 — Zyxel Multiple NAS Devices OS Command Injection Vulnerability

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 authent

01What is this vulnerability?

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…

02Affected products

Vendor	Product	Versions
ZyXEL	NAS326	V5.21(AAZF.7)C0
ZyXEL	NAS520	V5.21(AASZ.3)C0
ZyXEL	NAS540	V5.21(AATB.4)C0
ZyXEL	NAS542	V5.21(ABAG.4)C0
ZyXEL	NSA210	all
ZyXEL	NSA220	all
ZyXEL	NSA220+	all
ZyXEL	NSA221	all
ZyXEL	NSA310	V4.75(AALH.2)C0
ZyXEL	NSA320	all
ZyXEL	NSA320S	V4.75(AANV.2)C0
ZyXEL	NSA325	V4.81(AAAJ.1)C0
ZyXEL	NSA325v2	V4.81(AALS.1)C0

03Active exploitation status

Yes — actively exploited. Added to the CISA KEV catalog on 2022-03-25. Ransomware use: Unknown.

04Recommended remediation

• Patch to a fixed version listed in the vendor advisory (see references below).
• Mitigate with WAF rules, network egress filters, or feature flags where the patch is not yet available.
• Hunt historical logs for exploitation indicators — see Detection signatures below.

05Technical details

For the full vendor write-up, exploit chains, and reference implementations, see the references list in section 09.

06Detection signatures

Open the Sigma generator with a pre-filled prompt for this CVE to draft a starting detection in your stack of choice:

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07Related CVEs

No directly-cited follow-up CVEs in the KB record for this advisory. The references list in section 09 carries the vendor cross-references.

08Timeline

• Published: 2020-03-04T19:30:18.400Z
• Last modified: 2025-10-21T23:35:50.221Z
• Added to CISA KEV: 2022-03-25
• BOD 22-01 due: 2022-04-15

09References

• cwe.mitre.org — https://cwe.mitre.org/data/definitions/78.html
• www.zyxel.com — https://www.zyxel.com/support/remote-code-execution-vulnerability-of-NAS-product…
• kb.cert.org — https://kb.cert.org/vuls/id/498544/
• kb.cert.org — https://kb.cert.org/artifacts/cve-2020-9054.html
• krebsonsecurity.com — https://krebsonsecurity.com/2020/02/zyxel-fixes-0day-in-network-storage-devices/