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Findings

CVE-2020-9054

Zyxel Multiple NAS Devices OS Command Injection Vulnerability

Published Mar 4, 2020 · updated Oct 8, 2026 · zyxel nas326 firmware

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

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Mar 4, 2020 · Catalog

    Detected

    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

  2. Mar 25, 2022 · CISA KEV

    Known exploited

    Apply updates per vendor instructions.

  3. Apr 15, 2022 · CISA KEV

    Remediation due

    Apply updates per vendor instructions.

  4. Oct 8, 2026 · Catalog

    Updated

    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

Required action

Apply updates per vendor instructions.

CISA due date Apr 15, 2022

Affected

  • cpe zyxel/atp100 firmwareversion unspecified
  • cpe zyxel/atp200 firmwareversion unspecified
  • cpe zyxel/atp500 firmwareversion unspecified
  • cpe zyxel/atp800 firmwareversion unspecified
  • cpe zyxel/nas326 firmwareversion unspecified
  • cpe zyxel/nas520 firmwareversion unspecified
  • cpe zyxel/nas540 firmwareversion unspecified
  • cpe zyxel/nas542 firmwareversion unspecified
  • cpe zyxel/usg20-vpn firmwareversion unspecified
  • cpe zyxel/usg20w-vpn firmwareversion unspecified
  • cpe zyxel/usg40 firmwareversion unspecified
  • cpe zyxel/usg40w firmwareversion unspecified
  • vendor Zyxel Multiple Network-Attached Storage (NAS) Devicesversion unspecified

Sources

  • CISA KEVConfirmed exploitationCVE-2020-9054

    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.

    cisa.gov
  • CVE.orgVulnerability recordCVE-2020-9054

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2020-9054

    30-day exploitation probability 100.0%

    first.org
  • NIST NVDVulnerability recordCVE-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 authent

    nvd.nist.gov

References