Skip to content
Noroxi
CVE-2020-9054· NVD / CVE Program· CNA certcc

ZyXEL NAS products running firmware version 5.21 and earlier are vulnerable to pre-authentication command injection in weblogin.cgi

Noroxi assessment

Priority: Now (action score 99/100)

  • CISA has confirmed exploitation in the wild (Mar 25, 2022). Remediation deadline for US federal agencies: Apr 15, 2022.
  • A ready-made attack module is public (Nuclei); exploiting it takes no special expertise.
  • Probability of exploitation in the next 30 days: 99.9% (FIRST EPSS); higher than 99.9% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to the record, no fixed version is available yet.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Patch today or shut off access. Until a fix is released, restrict access to the affected component and follow the vendor's advisory.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · CISA KEV · FIRST EPSS

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

CriticalCVSS 9.8 · v3.1KEVWeaponized No fix recorded
Published
Mar 4, 2020
Updated
Oct 8, 2026
EPSS
99.9% · 99th percentile

Report tools

JSON

Action score

99

Now

Patch today or shut off access.

CVSS
39 / 40 · 9.8 / 10
CISA KEV
30 / 30 · Listed
EPSS
30 / 30 · 99.9%

CISA SSVC decision

Exploitation
active
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
9.8
CNA · certcc
9.8
agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Actively exploited in the wild

CISA added this to its Known Exploited Vulnerabilities catalog on Mar 25, 2022. That signals real attacks, not theory.

Remediation deadline for US federal agencies: Apr 15, 2022.

Get told when this record changes

  • In CISA KEV: exploitation in the wild confirmed
  • Weaponized exploit exists
  • No fixed version yet

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2020-9054

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

One daily email digest (06:00 UTC); connect a webhook for KEV listings and weaponized exploits instantly.

Your free account also gets you

Running WordPress? Scan your site free with WP Lens

  • Stack alerts: add the products and versions you run, get the new CVEs that affect them
  • Uptime monitoring: 1 site, instant email when it goes down
  • Add your domain: subdomains and takeover risk scanned every week (1 domain)
  • 10 scans an hour on the security tools (3 a day without an account), an API key and MCP
  • All your scans in one panel: findings, what changed in the last scan, a report per domain or per client (PDF, share link)
All free tools

Sign up with email · Have an account? Sign in

Free account, no card. Unfollow any time.

Don't want an account? Get "Exploited this week" by email every MondayDon't want an account? RSS feed for zyxel records

Running WordPress? Scan your site free with WP Lens

Is your version affected? Check it

Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

We use this product, ask for help

Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
zyxelusg60w firmware
zyxelnas326 firmware
zyxelnas326
zyxelnas520 firmware
zyxelnas520
zyxelnas540 firmware
zyxelnas540
zyxelnas542 firmware
zyxelnas542
zyxelatp100 firmware
zyxelatp100
zyxelatp200 firmware

and 42 more

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • zyxel atp100 firmware4.35 and later · before 4.35\(abps.3\)c0
  • zyxel atp200 firmware4.35 and later · before 4.35\(abfw.3\)c0
  • zyxel atp500 firmware4.35 and later · before 4.35\(abfu.3\)c0
  • zyxel atp800 firmware4.35 and later · before 4.35\(abiq.3\)c0
  • zyxel nas326 firmwarebefore 5.21\(aazf.10\)c0
  • zyxel nas520 firmwarebefore 5.21\(aasz.3\)c0
  • zyxel nas540 firmwarebefore 5.21\(aatb.7\)c0
  • zyxel nas542 firmwarebefore 5.21\(abag.7\)c0
  • zyxel usg110 firmware4.35 and later · before 4.35\(aaph.3\)c0
  • zyxel usg1100 firmware4.35 and later · before 4.35\(aapk.3\)c0
  • zyxel usg1900 firmware4.35 and later · before 4.35\(aapl.3\)c0
  • zyxel usg20-vpn firmware4.35 and later · before 4.35\(abaq.3\)c0
  • zyxel usg20w-vpn firmware4.35 and later · before 4.35\(abar.3\)c0
  • zyxel usg210 firmware4.35 and later · before 4.35\(aapi.3\)c0
  • zyxel usg2200 firmware4.35 and later · before 4.35\(abae.3\)c0
  • zyxel usg310 firmware4.35 and later · before 4.35\(aapj.3\)c0
  • zyxel usg40 firmware4.35 and later · before 4.35\(aala.3\)c0
  • zyxel usg40w firmware4.35 and later · before 4.35\(aalb.3\)c0
  • zyxel usg60 firmware4.35 and later · before 4.35\(aaky.3\)c0
  • zyxel usg60w firmware4.35 and later · before 4.35\(aakz.3\)c0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (certcc). Independent of NVD's CPE analysis and usually ahead of it.

  • ZyXEL NAS326

    • V5.21(AAZF.7)C0 and later · up to and including V5.21(AAZF.7)C0affected

  • ZyXEL NAS520

    • V5.21(AASZ.3)C0 and later · up to and including V5.21(AASZ.3)C0affected

  • ZyXEL NAS540

    • V5.21(AATB.4)C0 and later · up to and including V5.21(AATB.4)C0affected

  • ZyXEL NAS542

    • V5.21(ABAG.4)C0 and later · up to and including V5.21(ABAG.4)C0affected

  • ZyXEL NSA210

    • allaffected

  • ZyXEL NSA220

    • allaffected

  • ZyXEL NSA220+

    • allaffected

  • ZyXEL NSA221

    • allaffected

  • ZyXEL NSA310

    • V4.75(AALH.2)C0 and later · up to and including V4.75(AALH.2)C0affected

  • ZyXEL NSA320

    • allaffected

  • ZyXEL NSA320S

    • V4.75(AANV.2)C0 and later · up to and including V4.75(AANV.2)C0affected

  • ZyXEL NSA325

    • V4.81(AAAJ.1)C0 and later · up to and including V4.81(AAAJ.1)C0affected

Same product

zyxel: all records

Other highest-scoring records for the same primary product.

  • CVE-2023-27992The pre-authentication command injection vulnerability in the Zyxel NAS326 firmware versions prior to V5.21(AAZF.14)C0, NAS540 firmware versKEV
    94Now
  • CVE-2024-29972** UNSUPPORTED WHEN ASSIGNED ** The command injection vulnerability in the CGI program "remote_help-cgi" in Zyxel NAS326 firmware versions b
    66This week
  • CVE-2024-29973** UNSUPPORTED WHEN ASSIGNED ** The command injection vulnerability in the “setCookie” parameter in Zyxel NAS326 firmware versions before V5
    65This week

Published before and after this one in the same product

  • ← EarlierCVE-2019-10633Apr 9, 2019 · An eval injection vulnerability in the Python web server routing on the Zyxel NAS 326 version 5.21 and below allows a remote authenticated a
    36Monitor
  • ← EarlierCVE-2019-10634Apr 9, 2019 · An XSS vulnerability in the Zyxel NAS 326 version 5.21 and below allows a remote authenticated attacker to inject arbitrary JavaScript or HT
    21Monitor
  • Later →CVE-2020-13364Aug 6, 2020 · A backdoor in certain Zyxel products allows remote TELNET access via a CGI script.
    35Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

Weaponized

A ready exploit tool or active in-the-wild use is known for this vulnerability. This should be your top priority.

Evidence

  • Nuclei detection template ×1
  • Proof-of-concept repository on GitHub ×1

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Nuclei detection templateNuclei template CVE-2020-9054 —
Proof-of-concept repository on GitHubstars:32021-09-09

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. First PoC+553 d
  3. CISA KEV+750 d
  4. TodayOct 25, 2026+2425 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

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

CVSS vector

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

nvd-primary

Root cause

User input is inserted as text into a shell command. The shell may interpret special characters in the input as part of the command.

The bug in code

The whole CWE-78 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

ts
const host = req.body.host;exec("ping -c 1 " + host, onResult);

Fixed

ts
const host = req.body.host;if (!/^[a-z0-9.-]{1,253}$/i.test(host)) return res.sendStatus(400);execFile("ping", ["-c", "1", host], onResult);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

Show all references (4 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records