⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Critical · CVSS 10 ⚠ ACTIVELY EXPLOITED — CISA KEV

How to Fix CVE-2020-2021: Improper Verification of Cryptographic Signature in Palo Alto Networks PAN-OS

By Sai Kiran Pandrala

⚡ At a glance
SeverityCVSS 10 (Critical)
Actively exploited?Yes, listed in CISA KEV (added 2022-03-25, federal due date 2022-04-15). Known ransomware use.
AffectedPAN-OS: 8.0.*, 8.1 < version 8.1.15, 9.0 < version 9.0.9, 9.1 < version 9.1.3
Fixed inPAN-OS: 8.1.15, 9.0.9, 9.1.3
Type (CWE)CWE-347: Improper Verification of Cryptographic Signature
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-2020-2021?

When Security Assertion Markup Language (SAML) authentication is enabled and the 'Validate Identity Provider Certificate' option is disabled (unchecked), improper verification of signatures in PAN-OS SAML authentication enables an unauthenticated network-based attacker to access protected resources. The attacker must have network access to the vulnerable server to exploit this vulnerability. This issue affects PAN-OS 9.1 versions earlier than PAN-OS 9.1.3; PAN-OS 9.0 versions earlier than PAN-OS 9.0.9; PAN-OS 8.1 versions earlier than PAN-OS 8.1.15, and all versions of PAN-OS 8.0 (EOL). This issue does not affect PAN-OS 7.1. This issue cannot be exploited if SAML is not used for authentication.

A successful exploit lets a remote attacker run arbitrary code on the target system. The fix is to install the patched build of Palo Alto Networks PAN-OS listed in the table above, then confirm the running version after the upgrade.

Am I affected?

Check your installed version of Palo Alto Networks PAN-OS 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-2020-2021

The remediation is the patched build of Palo Alto Networks PAN-OS. 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.

PAN-OS (CLI)


admin@PA> show system info | match sw-version
admin@PA> request system software check
admin@PA> request system software download version 8.1.15
admin@PA> request system software install version 8.1.15
admin@PA> request restart system

Panorama push


Panorama -> Device Deployment -> Software -> Check Now -> Download 8.1.15 -> Install -> Reboot

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


<#
.SYNOPSIS  Remediates CVE-2020-2021 on Windows hosts.
.DESCRIPTION
  Detects current version of PAN-OS, takes a config backup, applies the patched build
  (8.1.15), 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-2020-2021-$(Get-Date -Format yyyyMMdd-HHmmss).log"

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

    Write-Host '[2/5] Backup config directory if present'
    $cfg = "$env:ProgramFiles\PAN-OS"
    if (Test-Path $cfg) {
        $bak = "$logDir\CVE-2020-2021-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.PAN-OS> --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\PAN-OS" -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-2020-2021 remediation complete"
} catch {
    Write-Error "CVE-2020-2021 remediation FAILED: $_"
    exit 1
} finally {
    Stop-Transcript
}

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


#!/usr/bin/env bash
# remediate-cve-2020-2021.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="$LOG/CVE-2020-2021-$STAMP.log"
exec > >(tee -a "$LOGFILE") 2>&1

echo "[1/5] Detect installed PAN-OS"
if command -v dpkg >/dev/null 2>&1; then
    dpkg -l | grep -i "pan-os" || true
elif command -v rpm >/dev/null 2>&1; then
    rpm -qa | grep -i "pan-os" || true
fi

echo "[2/5] Backup config"
for d in /etc/pan-os /opt/pan-os /usr/local/pan-os; do
    if [[ -d "$d" ]]; then
        tar czf "$LOG/CVE-2020-2021-$(basename $d)-$STAMP.tgz" "$d"
        echo "  Backup -> $LOG/CVE-2020-2021-$(basename $d)-$STAMP.tgz"
    fi
done

echo "[3/5] Apply patch (target: 8.1.15)"
if command -v apt-get >/dev/null 2>&1; then
    sudo apt-get update
    sudo apt-get install --only-upgrade "pan-os" -y
elif command -v dnf >/dev/null 2>&1; then
    sudo dnf upgrade "pan-os" --security -y
elif command -v yum >/dev/null 2>&1; then
    sudo yum update "pan-os" --security -y
elif command -v zypper >/dev/null 2>&1; then
    sudo zypper patch --category security
fi

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

echo "[5/5] CVE-2020-2021 remediation script complete. Log: $LOGFILE"

If you can't patch immediately

Restrict the management plane (Windows firewall, PowerShell)


New-NetFirewallRule -DisplayName 'Restrict-mgmt-CVE-2020-2021' -Direction Inbound -Action Block -Protocol TCP -LocalPort 443,8443,3389 -RemoteAddress Any
New-NetFirewallRule -DisplayName 'Allow-mgmt-admin-allowlist' -Direction Inbound -Action Allow -Protocol TCP -LocalPort 443,8443,3389 -RemoteAddress 10.0.0.0/24

Restrict the management plane (Linux nftables)


sudo nft add table inet filter 2>/dev/null || true
sudo nft 'add chain inet filter input { type filter hook input priority 0; }' 2>/dev/null || true
sudo nft add rule inet filter input ip saddr 10.0.0.0/24 tcp dport { 443, 8443, 22 } accept
sudo nft add rule inet filter input tcp dport { 443, 8443, 22 } drop

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-2020-2021 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

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

Is CVE-2020-2021 being exploited right now?

Yes. CVE-2020-2021 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-2020-2021?

CVSS 10 (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

*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.*