How to Fix CVE-2020-9054: OS Command Injection in Zyxel Multiple Network-Attached Storage (NAS) Devices

By Sai Kiran Pandrala

Actively exploited. Listed in the CISA Known Exploited Vulnerabilities catalog since 2022-03-25; federal civilian agencies must remediate by 2022-04-15. Patch on an emergency cycle if the system is internet-exposed.

What is CVE-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 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 used to run any command with root privileges.

A successful exploit lets a remote attacker run arbitrary code on the target system. The fix is to install the patched build of Zyxel Multiple Network-Attached Storage (NAS) Devices listed in the table above, then confirm the running version after the upgrade.

Am I affected?

Check your installed version of Zyxel Multiple Network-Attached Storage (NAS) Devices against the Affected row above. If the build sits inside any of those ranges, treat the host as vulnerable until patched.

Read the version the same way you would for any maintenance task: the management console About page, the CLI version command, or the package manager record for the installed binary. The vendor advisory linked in the references is the authoritative source for the affected-build matrix.

How to fix CVE-2020-9054

The remediation is the patched build of Zyxel Multiple Network-Attached Storage (NAS) Devices. The blocks below give you runnable commands for the platforms that ship this product, plus a full PowerShell and Bash script you can drop into your patch automation.

Zyxel (web UI)

Maintenance -> Firmware Upgrade -> Browse for ZLD .bin -> Upload -> Reboot
# Required ZLD build: V5.21 or later

Zyxel CLI (SSH)

show version
firmware-upgrade ftp://10.0.0.5/v5.21.bin
reboot

Full PowerShell remediation script (detect, back up, patch, verify, log)

<#
.SYNOPSIS  Remediates CVE-2020-9054 on Windows hosts.
.DESCRIPTION
  Detects current version of Multiple Network-Attached Storage (NAS) Devices, takes a config backup, applies the patched build
  (V5.21), confirms the upgrade, and writes a transcript to %ProgramData%\Patching.
#>
$ErrorActionPreference = 'Stop'
$logDir = "$env:ProgramData\Patching"
New-Item -ItemType Directory -Force -Path $logDir | Out-Null
Start-Transcript -Path "$logDir\CVE-2020-9054-$(Get-Date -Format yyyyMMdd-HHmmss).log"

try {
    Write-Host '[1/5] Detecting current version'
    $svc = Get-Service | Where-Object { $_.DisplayName -match 'Multiple' } | Select-Object -First 1
    if ($svc) { Write-Host "  Service: $($svc.Name) state=$($svc.Status)" }

    Write-Host '[2/5] Backup config directory if present'
    $cfg = "$env:ProgramFiles\Multiple"
    if (Test-Path $cfg) {
        $bak = "$logDir\CVE-2020-9054-backup-$(Get-Date -Format yyyyMMdd-HHmmss).zip"
        Compress-Archive -Path $cfg -DestinationPath $bak -Force
        Write-Host "  Backup -> $bak"
    }

    Write-Host '[3/5] Apply patch'
    try {
        winget upgrade --id <vendor.Multiple> --accept-source-agreements --accept-package-agreements --silent
    } catch {
        Write-Warning "winget upgrade failed: $_  -- falling back to MSU/MSI installer"
        Start-Process msiexec.exe -ArgumentList '/i "C:\Temp\patched.msi" /qn /norestart' -Wait
    }

    Write-Host '[4/5] Verify version'
    Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5
    # Adapt the next line to your product's version file:
    Get-ChildItem "$env:ProgramFiles\Multiple" -Recurse -Filter *.exe -ErrorAction SilentlyContinue |
        Select-Object -First 1 | ForEach-Object { $_.VersionInfo.FileVersion }

    Write-Host '[5/5] Restart service if needed'
    if ($svc) { Restart-Service $svc.Name }
    Write-Host "CVE-2020-9054 remediation complete"
} catch {
    Write-Error "CVE-2020-9054 remediation FAILED: $_"
    exit 1
} finally {
    Stop-Transcript
}

Full Bash remediation script (detect, back up, patch, verify, log)

#!/usr/bin/env bash
# remediate-cve-2020-9054.sh — detect, back up, patch, verify.
set -euo pipefail
LOG="/var/log/patching"
mkdir -p "$LOG"
STAMP="$(date +%Y%m%d-%H%M%S)"
LOGFILE="$LOG/CVE-2020-9054-$STAMP.log"
exec > >(tee -a "$LOGFILE") 2>&1

echo "[1/5] Detect installed Multiple Network-Attached Storage (NAS) Devices"
if command -v dpkg >/dev/null 2>&1; then
    dpkg -l | grep -i "multiple" || true
elif command -v rpm >/dev/null 2>&1; then
    rpm -qa | grep -i "multiple" || true
fi

echo "[2/5] Backup config"
for d in /etc/multiple /opt/multiple /usr/local/multiple; do
    if [[ -d "$d" ]]; then
        tar czf "$LOG/CVE-2020-9054-$(basename $d)-$STAMP.tgz" "$d"
        echo "  Backup -> $LOG/CVE-2020-9054-$(basename $d)-$STAMP.tgz"
    fi
done

echo "[3/5] Apply patch (target: V5.21)"
if command -v apt-get >/dev/null 2>&1; then
    sudo apt-get update
    sudo apt-get install --only-upgrade "multiple" -y
elif command -v dnf >/dev/null 2>&1; then
    sudo dnf upgrade "multiple" --security -y
elif command -v yum >/dev/null 2>&1; then
    sudo yum update "multiple" --security -y
elif command -v zypper >/dev/null 2>&1; then
    sudo zypper patch --category security
fi

echo "[4/5] Verify"
if systemctl status "multiple" >/dev/null 2>&1; then
    sudo systemctl restart "multiple"
    systemctl is-active "multiple"
fi
command -v "multiple" >/dev/null 2>&1 && "multiple" --version || true

echo "[5/5] CVE-2020-9054 remediation script complete. Log: $LOGFILE"

If you can't patch immediately

Disable the vulnerable service until patched (Linux)

# Vendor advisory: https://www.zyxel.com/support/remote-code-execution-vulnerability-of-NAS-products.shtml
sudo systemctl disable --now <vulnerable-service>
# Confirm no listener remains on the affected port
sudo ss -lntp | grep -E ':(443|22|8080|3306)' || echo 'No listener on common mgmt ports'

How to verify the fix worked

1. Re-run the version command from the fix section. The output must match the patched build listed in the vendor advisory for your branch.
2. Re-run an authenticated vulnerability scan (Nessus, Qualys, OpenVAS, Defender Vulnerability Management) targeting the patched host. CVE-2020-9054 must no longer be reported.
3. Pull the latest service logs and search for the exploitation signatures in the vendor advisory. Treat any match before the patch timestamp as a possible compromise: isolate the host, rotate credentials the affected process could see, and run a full IR triage.
4. Confirm any compensating control you put in place (firewall rules, sysctl, registry edits) is either intentionally left in place or rolled back, with the change documented in your CMDB.

Frequently asked questions

Related fixes

Other vulnerabilities in the same area that are worth patching alongside this one:

• How to Fix CVE-2020-25078: Security Vulnerability in DCS-2530L and DCS-2670L Devices — Security Vulnerability in DCS-2530L and DCS-2670L Devices
• How to Fix CVE-2020-4430: Obtain Information in Data Risk Manager — Obtain Information in Data Risk Manager
• How to Fix CVE-2020-11652: n/a in n/a , n/a in n/a
• How to Fix CVE-2020-5135: Buffer Overflow in SonicWall SonicOS , Buffer Overflow in SonicWall SonicOS
• How to Fix CVE-2020-13965: Cross-Site Scripting in Webmail , Cross-Site Scripting in Webmail

Is CVE-2020-9054 being exploited right now?

Yes. CVE-2020-9054 is in the CISA Known Exploited Vulnerabilities catalog, added 2022-03-25. CISA only lists CVEs with confirmed active exploitation.

What is the CVSS score for CVE-2020-9054?

CVSS 9.8 (Critical). Use it together with your exposure picture (internet-facing first, then DMZ, then internal) when you set the patch order.

Can I run the fix without downtime?

It depends on the platform. Network appliances often support hitless HA upgrades (upgrade the standby, fail over, upgrade the former primary). Application servers usually need a service restart. Clustered services (Elasticsearch, Tomcat behind a load balancer, MySQL replicas) tolerate a rolling upgrade. Schedule a maintenance window if HA is not in place.

What if my version is not in the affected list?

Re-check the build string in the vendor advisory linked below. CVE records reflect the affected-products list at publication. Variants discovered later are added to the same advisory or a follow-up CVE.

References

• Official vendor advisory: https://www.zyxel.com/support/remote-code-execution-vulnerability-of-NAS-products.shtml
• NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2020-9054
• CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• https://cwe.mitre.org/data/definitions/78.html
• https://kb.cert.org/vuls/id/498544/
• https://kb.cert.org/artifacts/cve-2020-9054.html
• https://krebsonsecurity.com/2020/02/zyxel-fixes-0day-in-network-storage-devices/

*This guide was assembled from the official vendor advisory, NVD record, and CISA KEV listing on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*