⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● High · CVSS 7.2 ⚠ ACTIVELY EXPLOITED — CISA KEV

How to Fix CVE-2020-5741: Deserialization of Untrusted Data in Plex Media Server (Windows)

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

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityCVSS 7.2 - High
Actively exploited?Yes, listed in CISA KEV (added 2023-03-10)
AffectedPlex Media Server (Windows): Versions prior to 1.19.3
Fixed inSee vendor advisory for the patched build
Type (CWE)CWE-502 Deserialization of Untrusted Data
Patch immediately. CISA's Known Exploited Vulnerabilities catalog lists this CVE, which means active exploitation has been confirmed. CISA KEV entry added 2023-03-10, federal due date 2023-03-31.

What is CVE-2020-5741?

CVE-2020-5741 is a deserialization of untrusted data in Plex Media Server (Windows) from Plex. Deserialization of Untrusted Data in Plex Media Server on Windows allows a remote, authenticated attacker to execute arbitrary Python code.

Why this CVE matters

This CVE sits on CISA's Known Exploited Vulnerabilities catalog, which only happens after active exploitation is observed in the wild. The deserialization of untrusted data class of flaw gives attackers a reliable foothold against vulnerable instances of Plex Media Server (Windows). If your deployment matches the affected versions, treat any window of unpatched exposure as compromise-likely and review logs accordingly.

Am I affected?

Run the version check that matches your platform. If the installed build sits inside the affected range from the table above, the fix applies to you.


# Linux package check
dpkg -s python3 2>/dev/null | grep -i version    # Debian / Ubuntu
rpm -q python3 2>/dev/null                       # RHEL / Rocky


# Windows version check
Get-CimInstance Win32_Product | Where-Object { $_.Name -match 'Plex Media Server (Windows)' } | Select-Object Name,Version

How to fix CVE-2020-5741

Apply the patched build the vendor names in the advisory. The commands below are starting points keyed to common platforms - adapt the package name and target version to your environment.

Ubuntu / Debian


sudo apt-get update
sudo apt-get install --only-upgrade python3
# verify the package version matches the fixed release in the advisory
dpkg -s python3 | grep -i version

RHEL / CentOS / Rocky / AlmaLinux


sudo dnf upgrade --refresh python3 -y
rpm -q python3

Container image


# Vendor advisory: https://www.tenable.com/security/research/tra-2020-32
# Pull the patched base image and rebuild
docker pull <your-registry>/python3:<patched-tag>
docker build -t <your-app>:patched .
docker stop <your-app> && docker rm <your-app>
docker run -d --name <your-app> <your-app>:patched

Windows (PowerShell, run as administrator)


# Vendor advisory: https://www.tenable.com/security/research/tra-2020-32
# Make sure Windows Update is current. For monthly rollups this is the safest path.
Install-Module -Name PSWindowsUpdate -Force -SkipPublisherCheck -Confirm:$false
Import-Module PSWindowsUpdate
Get-WindowsUpdate -KBArticleID <KB-from-advisory>
Install-WindowsUpdate -KBArticleID <KB-from-advisory> -AcceptAll -AutoReboot

# Confirm the KB landed
Get-HotFix | Where-Object { $_.HotFixID -eq 'KB<id>' }

# Or, for an MSU file downloaded from the Microsoft Update Catalog:
wusa.exe C:\Patches\windows10.0-kb<id>-x64.msu /quiet /norestart
shutdown /r /t 60

PowerShell detect/upgrade/verify/log (Windows)


# CVE-2020-5741 remediation runner — adapt the version checks to your environment.
$log = "C:\Logs\CVE-2020-5741-fix.log"
New-Item -ItemType Directory -Force -Path (Split-Path $log) | Out-Null
function Write-Log($msg) { "$(Get-Date -Format s) $msg" | Out-File $log -Append }

try {
    Write-Log "Detect: checking installed product"
    $installed = Get-CimInstance Win32_Product -ErrorAction SilentlyContinue |
        Where-Object { $_.Name -match 'Plex Media Server (Windows)' }
    if (-not $installed) { Write-Log "Product not installed; nothing to do"; return }
    Write-Log "Found version $($installed.Version)"

    Write-Log "Backup: copying program files and registry hive"
    $stamp = Get-Date -Format yyyyMMdd-HHmm
    $backup = "C:\Backup\CVE-2020-5741-$stamp"
    New-Item -ItemType Directory -Force -Path $backup | Out-Null
    Copy-Item $installed.InstallLocation $backup -Recurse -ErrorAction SilentlyContinue
    reg export HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall "$backup\uninstall.reg" /y | Out-Null

    Write-Log "Upgrade: install patched build via vendor MSI / Windows Update"
    # Example MSI:  Start-Process msiexec.exe -ArgumentList '/i C:\Patches\Plex Media Server (Windows)-patched.msi /qn /norestart' -Wait
    Install-WindowsUpdate -AcceptAll -AutoReboot -ErrorAction SilentlyContinue

    Write-Log "Verify: re-reading product version"
    $after = Get-CimInstance Win32_Product | Where-Object { $_.Name -match 'Plex Media Server (Windows)' }
    Write-Log "Post-patch version: $($after.Version)"
    if ($after.Version -ne $installed.Version) { Write-Log "SUCCESS: version changed" } else { Write-Log "WARN: version unchanged - check vendor advisory" }
} catch {
    Write-Log "ERROR: $_"
    throw
}

Bash detect/upgrade/verify/log (Linux)


#!/usr/bin/env bash
# CVE-2020-5741 remediation runner. Re-runnable, exits non-zero on failure.
set -euo pipefail
log() { printf '%s %s\n' "$(date -Is)" "$*" | tee -a /var/log/cve-2020-5741-fix.log; }

log "Detect: current python3 version"
if command -v dpkg >/dev/null 2>&1; then
    current=$(dpkg-query -W -f='${Version}' python3 2>/dev/null || echo "not-installed")
elif command -v rpm >/dev/null 2>&1; then
    current=$(rpm -q --qf '%{VERSION}-%{RELEASE}' python3 2>/dev/null || echo "not-installed")
else
    current="unknown"
fi
log "Current: $current"

log "Backup: snapshotting config"
backup="/var/backups/cve-2020-5741-$(date +%Y%m%d-%H%M)"
mkdir -p "$backup"
[ -d /etc/python3 ] && cp -a /etc/python3 "$backup/" || true

log "Upgrade: applying vendor patch"
if command -v apt-get >/dev/null 2>&1; then
    sudo apt-get update -qq
    sudo apt-get install -y --only-upgrade python3
elif command -v dnf >/dev/null 2>&1; then
    sudo dnf upgrade -y python3
elif command -v yum >/dev/null 2>&1; then
    sudo yum update -y python3
fi

log "Verify: re-reading python3 version"
if command -v dpkg >/dev/null 2>&1; then
    after=$(dpkg-query -W -f='${Version}' python3)
else
    after=$(rpm -q --qf '%{VERSION}-%{RELEASE}' python3)
fi
log "After: $after"

if [ "$after" != "$current" ]; then
    log "SUCCESS: python3 upgraded"
else
    log "WARN: version unchanged. Confirm the patched build is in your repository."
    exit 1
fi

After the upgrade, restart any service that loads the patched binary so the new code is actually running.

If you can't patch immediately

Patching is the only durable fix. These mitigations cut exposure while the change window is scheduled, they do not remove the vulnerability.

Restrict network exposure (iptables / nftables)


# Replace 10.0.0.0/8 with your management network. This drops everyone else.
sudo iptables -I INPUT -p tcp --dport 443 -s 10.0.0.0/8 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 443 -j DROP
sudo iptables-save | sudo tee /etc/iptables/rules.v4


# nftables equivalent
sudo nft add rule inet filter input tcp dport 443 ip saddr != 10.0.0.0/8 drop

Windows: disable the vulnerable feature via registry


# Vendor advisory: https://www.tenable.com/security/research/tra-2020-32
# Replace <Component> / <Setting> with the exact key from the vendor advisory.
# Always export the key first so you can roll back.
reg export "HKLM\SOFTWARE\Vendor\plex media server (windows)" "C:\Backup\preFix-CVE-2020-5741.reg" /y
Set-ItemProperty -Path "HKLM:\SOFTWARE\Vendor\plex media server (windows)" -Name "Disable<Setting>" -Value 1 -Type DWord
Restart-Service -Name "<service-name>" -Force

How to verify the fix worked

After applying the patched build, confirm the version string matches the fixed release named in the Plex advisory.


dpkg -s python3 | grep -i version       # Debian / Ubuntu
rpm -q python3                          # RHEL / Rocky


Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

Run an authenticated vulnerability scan with a current signature set and confirm the scanner no longer flags CVE-2020-5741. For internet-facing deployments that were unpatched during the disclosure window, review logs for the affected endpoints over the full exposure period and rotate any credentials the vulnerable process could touch.

Frequently asked questions

Is CVE-2020-5741 being exploited in the wild?

Yes. CISA added CVE-2020-5741 to the Known Exploited Vulnerabilities catalog, which means active exploitation has been confirmed.

Will a firewall rule or WAF signature fully mitigate CVE-2020-5741?

No. Network-layer filters slow opportunistic scanners and block a subset of payloads, but a focused attacker who knows the bug will work around them. The vendor patch is the only durable fix.

Do I need to assume compromise if the affected service was internet-facing and unpatched?

For a CVE that CISA confirms is under active exploitation, yes. Review logs for the affected endpoints over the entire exposure window, rotate credentials the vulnerable process could read, and look for unexpected accounts, scheduled tasks, or outbound connections.

References

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