# What is CVE-2020-9054?

> CVE-2020-9054 is a critical-severity flaw (CVSS 9.8) in Nas326 Firmware from Zyxel, published on 4 March 2020. It is on the list of flaws known to be exploited, so criminals are already using it. The latest forecast puts its chance of use in the next 30 days at over 99%. If you run an affected version, patch it first.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2020-9054

## At a glance

- **Verdict:** Fix this now. Attackers are using this flaw today. If you run an affected version, it goes to the top of your list.
- **Precursor Intelligence risk score:** 86 out of 100 (Critical); action: Emergency patch. Kept up to date as the evidence changes.
- **Severity:** Critical (CVSS 9.8 out of 10)
- **Known to be exploited:** Yes, it is on the government list of flaws known to be exploited
- **Chance of use in the next 30 days:** over 99% (latest exploit-likelihood forecast)
- **Published:** 4 March 2020
- **Record last updated:** 22 October 2025
- **Main product:** Nas326 Firmware from Zyxel
- **Affected products:** 27

## What is CVE-2020-9054? In plain terms

It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.

### The official 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

### What kind of flaw is it?

- CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

### How an attack on it works

- Where an attacker can be: Anywhere on the internet
- How hard it is to pull off: Easy: no special conditions
- Login needed first: No login needed
- Does someone have to click: No, nobody has to do anything
- What an attacker gets: Can read data, change data and take it offline

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

## Is CVE-2020-9054 being exploited? Yes

Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at over 99%.

Exploit likelihood over the last 7 days: >99%, >99%, >99%, >99%, >99%, >99%, >99%.

### Timeline

- 4 March 2020: Published
- 22 October 2025: Record last updated

### How Precursor Intelligence ranks it

CVE-2020-9054 scores **86 out of 100 (Critical)**, with the action "Emergency patch".

Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less:

- Evidence it is being exploited: biggest factor
- How severe it is: strong factor
- How widely exposed it is: smaller factor
- Threat activity around it: smaller factor

85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it.

## Who is affected by CVE-2020-9054?

The published record lists 27 products. Versions are as published: "before 5.21(aazf.7)c0" means every version up to, but not including, 5.21(aazf.7)c0.

- [Nas326 Firmware](https://www.precursorintelligence.com/product/zyxel/nas326_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 5.21(aazf.7)c0
- [Atp100 Firmware](https://www.precursorintelligence.com/product/zyxel/atp100_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(abps.3)c0
- [Atp200 Firmware](https://www.precursorintelligence.com/product/zyxel/atp200_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(abfw.3)c0
- [Atp500 Firmware](https://www.precursorintelligence.com/product/zyxel/atp500_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(abfu.3)c0
- [Atp800 Firmware](https://www.precursorintelligence.com/product/zyxel/atp800_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(abiq.3)c0
- [Nas520 Firmware](https://www.precursorintelligence.com/product/zyxel/nas520_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 5.21(aasz.3)c0
- [Nas540 Firmware](https://www.precursorintelligence.com/product/zyxel/nas540_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 5.21(aatb.4)c0
- [Nas542 Firmware](https://www.precursorintelligence.com/product/zyxel/nas542_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 5.21(abag.4)c0
- [Usg110 Firmware](https://www.precursorintelligence.com/product/zyxel/usg110_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(aaph.3)c0
- [Usg1100 Firmware](https://www.precursorintelligence.com/product/zyxel/usg1100_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(aapk.3)c0
- [Usg1900 Firmware](https://www.precursorintelligence.com/product/zyxel/usg1900_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(aapl.3)c0
- [Usg20-VPN Firmware](https://www.precursorintelligence.com/product/zyxel/usg20-vpn_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(abaq.3)c0
- [Usg20w-VPN Firmware](https://www.precursorintelligence.com/product/zyxel/usg20w-vpn_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(abar.3)c0
- [Usg210 Firmware](https://www.precursorintelligence.com/product/zyxel/usg210_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(aapi.3)c0
- [Usg2200 Firmware](https://www.precursorintelligence.com/product/zyxel/usg2200_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(abae.3)c0
- [Usg310 Firmware](https://www.precursorintelligence.com/product/zyxel/usg310_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(aapj.3)c0
- [Usg40 Firmware](https://www.precursorintelligence.com/product/zyxel/usg40_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(aala.3)c0
- [Usg40w Firmware](https://www.precursorintelligence.com/product/zyxel/usg40w_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(aalb.3)c0
- [Usg60 Firmware](https://www.precursorintelligence.com/product/zyxel/usg60_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(aaky.3)c0
- [Usg60w Firmware](https://www.precursorintelligence.com/product/zyxel/usg60w_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(aakz.3)c0
- [Vpn100 Firmware](https://www.precursorintelligence.com/product/zyxel/vpn100_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(abfv.3)c0
- [Vpn1000 Firmware](https://www.precursorintelligence.com/product/zyxel/vpn1000_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(abip.3)c0
- [Vpn300 Firmware](https://www.precursorintelligence.com/product/zyxel/vpn300_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(abfc.3)c0
- [Vpn50 Firmware](https://www.precursorintelligence.com/product/zyxel/vpn50_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(abhl.3)c0
- [Zywall110 Firmware](https://www.precursorintelligence.com/product/zyxel/zywall110_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(aaaa.3)c0
- [Zywall1100 Firmware](https://www.precursorintelligence.com/product/zyxel/zywall1100_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(aaac.3)c0
- [Zywall310 Firmware](https://www.precursorintelligence.com/product/zyxel/zywall310_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): 4.35 to before 4.35(aaab.3)c0

## How do I fix CVE-2020-9054?

1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
2. **Apply the vendor’s fix.** Install the update named in the vendor’s advisory. We’ve put the advisory first in the list.
3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
4. **Check it wasn’t used before you patched.** Because criminals are already using this flaw, look for signs of a break-in on affected systems using the vendor’s guidance.

### References

- [zyxel.com](https://www.zyxel.com/support/remote-code-execution-vulnerability-of-NAS-products.shtml) (Vendor advisory)
- [cwe.mitre.org](https://cwe.mitre.org/data/definitions/78.html) (Third-party advisory)
- [kb.cert.org](https://kb.cert.org/artifacts/cve-2020-9054.html) (Third-party advisory, Government resource)
- [kb.cert.org](https://kb.cert.org/vuls/id/498544/) (Third-party advisory, Government resource)
- [krebsonsecurity.com](https://krebsonsecurity.com/2020/02/zyxel-fixes-0day-in-network-storage-devices/) (Exploit, Third-party advisory)
- [cisa.gov](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-9054)

## Questions

### What is CVE-2020-9054?

CVE-2020-9054 is a critical-severity flaw in Nas326 Firmware from Zyxel, published on 4 March 2020. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.

### How serious is CVE-2020-9054?

It scores 9.8 out of 10 on the CVSS severity scale, which is critical. Our risk score for CVE-2020-9054 is 86 out of 100, which is Critical. Its action is "Emergency patch". Attackers are using this flaw today. If you run an affected version, it goes to the top of your list.

### Is CVE-2020-9054 being exploited?

Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at over 99%.

### Which versions does CVE-2020-9054 affect?

For Nas326 Firmware from Zyxel: before 5.21(aazf.7)c0. The record lists 27 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2020-9054?

Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet. Because criminals are already using it, also check affected systems for signs of a break-in.

## Does CVE-2020-9054 affect you?

Precursor Intelligence keeps checking for you:

- **Tell us what you run.** Pick your software from a list, or let us work it out from your website.
- **We match it to every flaw.** Over 400,000 published flaws, checked against your list.
- **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it.
- **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools.

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