● Medium · CVSS 5.3

How to Fix CVE-2026-0540: Cross-site scripting in DOMPurify

By Sai Kiran Pandrala. Last verified: 2026-05-25.

CVE-2026-0540 is a cross-site scripting in cure53 DOMPurify. The fix is to apply the vendor patch noted below.

⚡ At a glance

Severity	5.3 (Medium)
Actively exploited?	No public listing in CISA KEV
Affected	DOMPurify 3.1.3 to <=3.3.1; DOMPurify 2.5.3 to <=2.5.8
Fixed in	See vendor advisory
Type (CWE)	CWE-79 Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting')

Exploitation status

CVE-2026-0540 is not currently on the CISA Known Exploited Vulnerabilities (KEV) catalog, so there is no U.S.-government-confirmed in-the-wild exploitation on record for it. That is no proof of safety, though, since CISA KEV tends to lag actual exploitation, so schedule the fix by severity instead of waiting for confirmation.

Public exploit availability: as of now, no public exploit or Metasploit module appears in the cited references. Unpublished or privately held exploits could still exist, so weak public availability is not a reason to deprioritise.

What is CVE-2026-0540?

DOMPurify 3.1.3 through 3.3.1 and 2.5.3 through 2.5.8, fixed in commit 2726c74, contain a cross-site scripting vulnerability that allows attackers to bypass attribute sanitization by exploiting five missing rawtext elements (noscript, xmp, noembed, noframes, iframe) in the SAFE_FOR_XML regex. Attackers can include payloads like </noscript><img src=x onerror=alert(1)> in attribute values to execute JavaScript when sanitized output is placed inside these unprotected rawtext contexts. The CVSS base score is 5.3 (Medium). The official advisory is at https://github.com/cure53/DOMPurify.

Spot the symptom

Check the version of DOMPurify you are running and compare it against the Affected row above (DOMPurify 3.1.3 to <=3.3.1; DOMPurify 2.5.3 to <=2.5.8). If your build sits inside the affected range, you must patch.

Run the version check that fits your platform:

# Linux package check
dpkg -s dompurify 2>/dev/null | grep -i ^Version
rpm -q dompurify 2>/dev/null
command -v dompurify >/dev/null && dompurify --version 2>/dev/null

# Windows (PowerShell)
Get-Package -Name "*DOMPurify*" -ErrorAction SilentlyContinue | Select-Object Name, Version
winget list --name "DOMPurify" 2>$null

How to fix CVE-2026-0540

Upgrade DOMPurify to a patched build: See vendor advisory. The vendor advisory is the source of truth for the exact fixed version.

Ubuntu / Debian

sudo apt-get update
sudo apt-get install --only-upgrade dompurify
dpkg -s dompurify | grep -i ^Version

RHEL / CentOS / Rocky / AlmaLinux

sudo dnf upgrade --refresh dompurify -y
# or for older releases:
sudo yum update dompurify -y
rpm -q dompurify

SUSE / openSUSE

sudo zypper refresh
sudo zypper update dompurify
rpm -q dompurify

Complete PowerShell remediation script (Windows)

# Fix script for CVE-2026-0540 affecting DOMPurify
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2026-0540-fix-$(Get-Date -Format yyyyMMdd-HHmmss).log"
New-Item -ItemType Directory -Force (Split-Path $LogPath) | Out-Null
Start-Transcript -Path $LogPath -Append

try {
    Write-Host "[1/4] Detect installed version"
    $pkg = Get-Package -Name "*DOMPurify*" -ErrorAction SilentlyContinue
    if ($pkg) { $pkg | Format-Table Name, Version }
    else { Write-Host "Not detected via Get-Package; try winget list" }

    Write-Host "[2/4] Backup configuration"
    $backup = "C:\Backup\dompurify-$(Get-Date -Format yyyyMMdd)"
    New-Item -ItemType Directory -Force $backup | Out-Null
    Get-ChildItem "C:\ProgramData\DOMPurify" -ErrorAction SilentlyContinue |
        Copy-Item -Destination $backup -Recurse -Force -ErrorAction SilentlyContinue

    Write-Host "[3/4] Apply the upgrade to See vendor advisory"
    winget upgrade --name "DOMPurify" --silent --accept-source-agreements --accept-package-agreements
    if ($LASTEXITCODE -ne 0) {
        # Fallback: pull latest via OS update channel
        Install-Module -Name PSWindowsUpdate -Force -SkipPublisherCheck -ErrorAction SilentlyContinue
        Import-Module PSWindowsUpdate
        Install-WindowsUpdate -MicrosoftUpdate -AcceptAll -IgnoreReboot
    }

    Write-Host "[4/4] Verify the patched build"
    winget list --name "DOMPurify"
    Write-Host "Patch applied. Reboot if prompted."
    exit 0
} catch {
    Write-Error "Patch failed: $_"
    exit 1
} finally {
    Stop-Transcript
}

Complete Bash remediation script (Linux)

#!/usr/bin/env bash
# Fix script for CVE-2026-0540 affecting DOMPurify
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2026-0540-fix-$(date +%Y%m%d-%H%M%S).log"
exec > >(tee -a "$LOG") 2>&1

echo "[1/4] Detect installed version"
if command -v dpkg >/dev/null; then
    dpkg -s dompurify 2>/dev/null | grep -i ^Version || echo "dompurify not installed via dpkg"
elif command -v rpm >/dev/null; then
    rpm -q dompurify || echo "dompurify not installed via rpm"
fi

echo "[2/4] Backup configuration"
BACKUP="/root/backup-cve-2026-0540-$(date +%Y%m%d)"
mkdir -p "$BACKUP"
for d in /etc/dompurify /etc/dompurify.d /etc/dompurify.conf; do
    [ -e "$d" ] && cp -a "$d" "$BACKUP/" || true
done

echo "[3/4] Apply the upgrade (target: See vendor advisory)"
if command -v apt-get >/dev/null; then
    apt-get update
    apt-get install --only-upgrade -y dompurify
elif command -v dnf >/dev/null; then
    dnf upgrade --refresh -y dompurify
elif command -v yum >/dev/null; then
    yum update -y dompurify
elif command -v zypper >/dev/null; then
    zypper --non-interactive update dompurify
fi

echo "[4/4] Verify the patched build"
if command -v dpkg >/dev/null; then
    dpkg -s dompurify 2>/dev/null | grep -i ^Version
elif command -v rpm >/dev/null; then
    rpm -q dompurify
fi
echo "Done. Restart any service that loaded the old library."

If you can't patch immediately

Apply at least one of the following inline controls until you can deploy the patched build. None replace the upgrade.

Restrict exposure with nftables (Linux)

# Allow only trusted CIDR to reach the affected service ports
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 tcp dport {80, 443} ip saddr != 10.0.0.0/8 drop'
sudo nft list ruleset

Block at the host firewall (Windows)

New-NetFirewallRule -DisplayName "Block-CVE-2026-0540" -Direction Inbound -Action Block -Protocol TCP -LocalPort 80,443 -RemoteAddress Any -Enabled True
Get-NetFirewallRule -DisplayName "Block-CVE-2026-0540"

Disable the affected service (Linux)

sudo systemctl stop dompurify 2>/dev/null || true
sudo systemctl disable dompurify 2>/dev/null || true

If the vendor advisory lists an official workaround, prefer that wording verbatim. If no workaround is published, the only safe remediation is the patch.

Full fix path

After upgrading, confirm the installed version matches the patched build and that no old library is still loaded by a long-running process.

# Linux
dpkg -s dompurify 2>/dev/null | grep -i ^Version
rpm -q dompurify 2>/dev/null || true
# Pid map check for old library handles
sudo lsof +c0 2>/dev/null | grep -i "DEL.*lib" || true

# Windows
Get-Package -Name "*DOMPurify*" | Select-Object Name, Version
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

Expected: the reported version is at or above See vendor advisory. Restart the affected service (systemctl restart <service> on Linux, or restart the Windows service) so it loads the patched binary.

Is CVE-2026-0540 actively exploited?

There is no public confirmation of exploitation in the wild listed in CISA KEV at the time of this writing. Patch anyway. Public exploits commonly follow disclosure within weeks.

Do I need to reboot after patching CVE-2026-0540?

For kernel and OS-level updates, yes. For most userland packages a systemctl restart <service> is enough on Linux, and restarting the Windows service or app on Windows. Any process that loaded the old library keeps using it until restarted.

What is the CVSS score for CVE-2026-0540?

5.3 (Medium). Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N.

Where is the official advisory for CVE-2026-0540?

The vendor advisory is at https://github.com/cure53/DOMPurify. The NVD record is at https://nvd.nist.gov/vuln/detail/CVE-2026-0540.

References

Official vendor advisory: https://github.com/cure53/DOMPurify
NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-0540
CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
Additional reference: https://github.com/cure53/DOMPurify/commit/302b51de22535cc90235472c52e3401bedd46f80
Additional reference: https://github.com/cure53/DOMPurify/releases/tag/3.3.2
Additional reference: https://fluidattacks.com/advisories/daft

Written by Sai Kiran Pandrala on 2026-05-25. Always confirm against the vendor's advisory before applying changes in production.

Related weaknesses in the same component worth addressing at the same time: