CVE-2020-9054

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

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data exposure, data tampering, service disruption.

In the wild

CISA lists this as exploited in real attacks. Treat as urgent.

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2020-02-18 00:00 UTC ReservedThe CVE id was reserved by its CNA
2. 2020-03-04 20:15 UTC PublishedDisclosed publicly on CVE.org and NVD
3. 2022-03-25 Exploited in the wildAdded to CISA's Known Exploited Vulnerabilities list
4. 2022-04-15 Remediation deadlineCISA's due date for federal agencies to fix it
5. 2026-10-08 13:38 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: yes, CISA lists it. This puts it above everything that is not.
• Exploit odds: 100.0% in the next 30 days (EPSS).
• Severity: 9.8 CRITICAL (CVSS).
• Fix: a patch or advisory is linked.
• It meets the bar for Drop everything: critical, and exploited or very likely to be.

Details

Published

2020-03-04 20:15 UTC

Last modified

2026-10-08 13:38 UTC

Added to CISA KEV

2022-03-25

Exploit probability

100.0% · EPSS, next 30 days

Weakness

CWE-78 · OS command injection

Record status

Analyzed

Affected

• Zyxel nas326 Firmware < 5.21\(aazf.10\)c0
• Zyxel nas520 Firmware < 5.21\(aasz.3\)c0
• Zyxel nas540 Firmware < 5.21\(aatb.7\)c0
• Zyxel nas542 Firmware < 5.21\(abag.7\)c0
• Zyxel atp100 Firmware < 4.35\(abps.3\)c0
• Zyxel atp200 Firmware < 4.35\(abfw.3\)c0
• Zyxel atp500 Firmware < 4.35\(abfu.3\)c0
• Zyxel atp800 Firmware < 4.35\(abiq.3\)c0

Attack profile CVSS 3.1 · 9.8

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2020-9054.md and follow it. Check whether this project is affected by CVE-2020-9054. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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