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
This vulnerability carries a CRITICAL severity rating with a CVSS v3.1 score of 9.8, indicating it can be exploited remotely over the network with relatively low complexity without requiring user interaction and does not require pre-existing privileges . The vulnerability impacts confidentiality (data exposure), integrity (unauthorized modifications), and availability (service disruption) for affected systems. Impacting 54 products from zyxel, from zyxel, from zyxel and 51 others, organizations running these solutions should prioritize assessment and patching.
Reported in 2020, this vulnerability emerged during an era marked by increased sophistication in supply chain attacks, cloud infrastructure vulnerabilities, and software-as-a-service (SaaS) security challenges. Security practices during this period emphasized zero-trust architectures, container security, and API protection.
2020-03-04T20:15:10.750
2025-11-10T14:37:04.570
Analyzed
CVSSv3.1: 9.8 (CRITICAL)
AV:N/AC:L/Au:N/C:C/I:C/A:C
10.0
10.0
| Type | Vendor | Product | Version/Range | Vulnerable? |
|---|---|---|---|---|
| Operating System | zyxel | nas326_firmware | < 5.21\(aazf.7\)c0 | Yes |
| Hardware | zyxel | nas326 | - | No |
| Operating System | zyxel | nas520_firmware | < 5.21\(aasz.3\)c0 | Yes |
| Hardware | zyxel | nas520 | - | No |
| Operating System | zyxel | nas540_firmware | < 5.21\(aatb.4\)c0 | Yes |
| Hardware | zyxel | nas540 | - | No |
| Operating System | zyxel | nas542_firmware | < 5.21\(abag.4\)c0 | Yes |
| Hardware | zyxel | nas542 | - | No |
| Operating System | zyxel | atp100_firmware | < 4.35\(abps.3\)c0 | Yes |
| Hardware | zyxel | atp100 | - | No |
| Operating System | zyxel | atp200_firmware | < 4.35\(abfw.3\)c0 | Yes |
| Hardware | zyxel | atp200 | - | No |
| Operating System | zyxel | atp500_firmware | < 4.35\(abfu.3\)c0 | Yes |
| Hardware | zyxel | atp500 | - | No |
| Operating System | zyxel | atp800_firmware | < 4.35\(abiq.3\)c0 | Yes |
| Hardware | zyxel | atp800 | - | No |
| Operating System | zyxel | usg20-vpn_firmware | < 4.35\(abaq.3\)c0 | Yes |
| Hardware | zyxel | usg20-vpn | - | No |
| Operating System | zyxel | usg20w-vpn_firmware | < 4.35\(abar.3\)c0 | Yes |
| Hardware | zyxel | usg20w-vpn | - | No |
| Operating System | zyxel | usg40_firmware | < 4.35\(aala.3\)c0 | Yes |
| Hardware | zyxel | usg40 | - | No |
| Operating System | zyxel | usg40w_firmware | < 4.35\(aalb.3\)c0 | Yes |
| Hardware | zyxel | usg40w | - | No |
| Operating System | zyxel | usg60_firmware | < 4.35\(aaky.3\)c0 | Yes |
| Hardware | zyxel | usg60 | - | No |
| Operating System | zyxel | usg60w_firmware | < 4.35\(aakz.3\)c0 | Yes |
| Hardware | zyxel | usg60w | - | No |
| Operating System | zyxel | usg110_firmware | < 4.35\(aaph.3\)c0 | Yes |
| Hardware | zyxel | usg110 | - | No |
| Operating System | zyxel | usg210_firmware | < 4.35\(aapi.3\)c0 | Yes |
| Hardware | zyxel | usg210 | - | No |
| Operating System | zyxel | usg310_firmware | < 4.35\(aapj.3\)c0 | Yes |
| Hardware | zyxel | usg310 | - | No |
| Operating System | zyxel | usg1100_firmware | < 4.35\(aapk.3\)c0 | Yes |
| Hardware | zyxel | usg1100 | - | No |
| Operating System | zyxel | usg1900_firmware | < 4.35\(aapl.3\)c0 | Yes |
| Hardware | zyxel | usg1900 | - | No |
| Operating System | zyxel | usg2200_firmware | < 4.35\(abae.3\)c0 | Yes |
| Hardware | zyxel | usg2200 | - | No |
| Operating System | zyxel | vpn50_firmware | < 4.35\(abhl.3\)c0 | Yes |
| Hardware | zyxel | vpn50 | - | No |
| Operating System | zyxel | vpn100_firmware | < 4.35\(abfv.3\)c0 | Yes |
| Hardware | zyxel | vpn100 | - | No |
| Operating System | zyxel | vpn300_firmware | < 4.35\(abfc.3\)c0 | Yes |
| Hardware | zyxel | vpn300 | - | No |
| Operating System | zyxel | vpn1000_firmware | < 4.35\(abip.3\)c0 | Yes |
| Hardware | zyxel | vpn1000 | - | No |
| Operating System | zyxel | zywall110_firmware | < 4.35\(aaaa.3\)c0 | Yes |
| Hardware | zyxel | zywall110 | - | No |
| Operating System | zyxel | zywall310_firmware | < 4.35\(aaab.3\)c0 | Yes |
| Hardware | zyxel | zywall310 | - | No |
| Operating System | zyxel | zywall1100_firmware | < 4.35\(aaac.3\)c0 | Yes |
| Hardware | zyxel | zywall1100 | - | No |
SecUtils normalizes and enriches National Vulnerability Database (NVD) records by standardizing vendor and product identifiers, aggregating vulnerability metadata from both NVD and MITRE sources, and providing structured context for security teams. For zyxel's affected products, we extract Common Platform Enumeration (CPE) data, Common Weakness Enumeration (CWE) classifications, CVSS severity metrics, and reference data to enable rapid vulnerability prioritization and asset correlation. This record contains no exploit code, proof-of-concept instructions, or attack methodologies—only defensive intelligence necessary for patch management, risk assessment, and security operations.