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

CVE-2020-9054 is rated critical with a CVSS v3.1 base score of 9.8 and affects Zyxel Multiple Network-Attached Storage (NAS) Devices, along with 27 other products in NVD’s configuration data. Per its scoring, it can be exploited over the network, without authentication, without any user interaction. The scored impact on confidentiality, integrity and availability is the highest available. CISA added it to its Known Exploited Vulnerabilities catalog on 2022-03-25, which means exploitation in the wild has been observed.

Vulnerability 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

Severity breakdown

CVSS v3.1 9.8: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

  • Attack vector: Network. Exploitable remotely over the network, with no need for local or physical access.
  • Attack complexity: Low. No special conditions; the attack can be repeated reliably.
  • Privileges required: None. No account or prior access is needed.
  • User interaction: None. No action from any user is needed.
  • Scope: Unchanged. Impact stays within the vulnerable component.
  • Confidentiality impact: High. Total loss of confidentiality; sensitive data can be fully disclosed.
  • Integrity impact: High. Total loss of integrity; data or system state can be fully modified.
  • Availability impact: High. Total loss of availability; the component can be shut down.

Underlying weakness

CWE-78: Improper Neutralization of Special Elements used in an OS Command

The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command before it is sent to a downstream component.

Affected products

  • Zyxel Nas326 Firmware: before 5.21\(aazf.10\)c0
  • Zyxel Nas520 Firmware: before 5.21\(aasz.3\)c0
  • Zyxel Nas540 Firmware: before 5.21\(aatb.7\)c0
  • Zyxel Nas542 Firmware: before 5.21\(abag.7\)c0
  • Zyxel Atp100 Firmware: from 4.35 before 4.35\(abps.3\)c0
  • Zyxel Atp200 Firmware: from 4.35 before 4.35\(abfw.3\)c0
  • Zyxel Atp500 Firmware: from 4.35 before 4.35\(abfu.3\)c0
  • Zyxel Atp800 Firmware: from 4.35 before 4.35\(abiq.3\)c0
  • Zyxel Usg20 VPN Firmware: from 4.35 before 4.35\(abaq.3\)c0
  • Zyxel Usg20w VPN Firmware: from 4.35 before 4.35\(abar.3\)c0
  • Zyxel Usg40 Firmware: from 4.35 before 4.35\(aala.3\)c0
  • Zyxel Usg40w Firmware: from 4.35 before 4.35\(aalb.3\)c0
  • Zyxel Usg60 Firmware: from 4.35 before 4.35\(aaky.3\)c0
  • Zyxel Usg60w Firmware: from 4.35 before 4.35\(aakz.3\)c0
  • Zyxel Usg110 Firmware: from 4.35 before 4.35\(aaph.3\)c0

References