How to Fix CVE-2026-20945: Cross-site scripting in Microsoft SharePoint Enterprise Server 2016

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

What is CVE-2026-20945?

Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Office SharePoint allows an authorized attacker to perform spoofing over a network.

Am I affected?

Run the version check that matches your platform:

# Windows
winget list | findstr /I "microsoft"
Get-WmiObject Win32_Product | Where-Object { $_.Name -like "*Microsoft SharePoint Enterprise Server 2016*" } | Select-Object Name, Version

Compare what you see against the Affected row above (Microsoft 16.0.0 to <16.0.5548.1003; Microsoft 16.0.0 to <16.0.10417.20114; Microsoft 16.0.0 to <16.0.19725.20210). If your build sits inside that range, you are exposed and should patch.

How to fix CVE-2026-20945

The primary fix is to upgrade Microsoft SharePoint Enterprise Server 2016 to the patched build. Use the commands for your platform below; the patched versions listed in the vendor advisory are: Microsoft SharePoint Enterprise Server 2016 16.0.5548.1003; Microsoft SharePoint Server 2019 16.0.10417.20114; Microsoft SharePoint Server Subscription Edition 16.0.19725.20210.

Windows (PowerShell, run as administrator)

# Check installed version
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

# Apply latest Microsoft security updates (Windows Update)
Install-Module -Name PSWindowsUpdate -Force -SkipPublisherCheck
Import-Module PSWindowsUpdate
Get-WindowsUpdate -MicrosoftUpdate
Install-WindowsUpdate -MicrosoftUpdate -AcceptAll -AutoReboot

# Or via winget for application-level patches
winget upgrade --all --accept-source-agreements --accept-package-agreements

If the affected component is a third-party application, identify the package and run:

winget upgrade --id <vendor.product>

Replace <vendor.product> with the actual winget identifier (run winget search Microsoft SharePoint Enterprise Server 2016 to find it).

Complete PowerShell remediation script (Windows)

# Fix script for CVE-2026-20945 affecting Microsoft SharePoint Enterprise Server 2016
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2026-20945-fix-$(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] Detecting installed version of Microsoft SharePoint Enterprise Server 2016"
    $pkg = winget list --id "Microsoft_SharePoint_Ent" 2>$null
    Write-Host $pkg

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

    Write-Host "[3/4] Applying upgrade to Microsoft SharePoint Enterprise Server 2016 16.0.5548.1003; Microsoft SharePo..."
    winget upgrade --id "Microsoft_SharePoint_Ent" --silent --accept-source-agreements --accept-package-agreements
    # Fallback: Windows Update for OS-level fixes
    if ($LASTEXITCODE -ne 0) {
        Install-Module -Name PSWindowsUpdate -Force -SkipPublisherCheck -ErrorAction SilentlyContinue
        Import-Module PSWindowsUpdate
        Install-WindowsUpdate -MicrosoftUpdate -AcceptAll -IgnoreReboot
    }

    Write-Host "[4/4] Verifying patched build"
    winget list --id "Microsoft_SharePoint_Ent"
    Write-Host "Fix 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-2026-20945 affecting Microsoft SharePoint Enterprise Server 2016
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2026-20945-fix-$(date +%Y%m%d-%H%M%S).log"
exec > >(tee -a "$LOG") 2>&1

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

echo "[2/4] Backing up configuration"
BACKUP="/root/backup-cve-2026-20945-$(date +%Y%m%d)"
mkdir -p "$BACKUP"
for d in /etc/microsoft /etc/microsoft.d /etc/microsoft.conf; do
    [ -e "$d" ] && cp -a "$d" "$BACKUP/" || true
done

echo "[3/4] Applying upgrade (target: Microsoft SharePoint Enterprise Server 2016 16.0.5548.1003; Microsoft SharePo...)"
if command -v apt-get >/dev/null; then
    apt-get update
    apt-get install --only-upgrade -y microsoft
elif command -v dnf >/dev/null; then
    dnf upgrade --security -y microsoft
elif command -v yum >/dev/null; then
    yum update -y microsoft
elif command -v zypper >/dev/null; then
    zypper --non-interactive patch --category security
fi

echo "[4/4] Verifying patched build"
if command -v dpkg >/dev/null; then
    dpkg -s microsoft 2>/dev/null | grep -i version
elif command -v rpm >/dev/null; then
    rpm -q microsoft
fi
echo "Done. Restart any running daemons that loaded the old library."

If you can't patch immediately

If you cannot apply the patched version today, restrict exposure with one of the following runnable controls. None replace the patch.

Windows firewall isolation

# Allow only management subnet to reach the vulnerable service
New-NetFirewallRule -DisplayName "Restrict Microsoft SharePoint Enterprise Server 2016" `
    -Direction Inbound -Action Block -RemoteAddress Any `
    -Protocol TCP -LocalPort 443
New-NetFirewallRule -DisplayName "Allow Mgmt Microsoft SharePoint Enterprise Server 2016" `
    -Direction Inbound -Action Allow -RemoteAddress 10.0.0.0/8 `
    -Protocol TCP -LocalPort 443

Service-level fallback

# If the affected feature is optional, stop the service until the patch is applied
sudo systemctl stop microsoft
sudo systemctl disable microsoft

How to verify the fix worked

# Linux
microsoft --version 2>/dev/null || dpkg -s microsoft | grep -i version
rpm -q microsoft 2>/dev/null || true

# Windows
winget list | findstr /I "microsoft"
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

Expected: the reported version is at or above Microsoft SharePoint Enterprise Server 2016 16.0.5548.1003; Microsoft SharePoint Server 2019 16.0.10417.20114; Microsoft SharePoint Server Subscription Edition 16.0.19725.20210. Restart any services that loaded the old library (systemctl restart <service> on Linux, restart the Windows service or reboot when prompted). For network appliances, run show version on the device and confirm the build matches the patched release.

Frequently asked questions

Related fixes

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

• How to Fix CVE-2026-32203: Stack buffer overflow in .NET 10.0 — Stack buffer overflow in .NET 10.0
• How to Fix CVE-2026-24283: Multiple UNC Provider Kernel Driver Elevation of Privilege — Multiple UNC Provider Kernel Driver Elevation of Privilege
• How to Fix CVE-2026-21513: Security Vulnerability in Windows 10 Version 1607 , Security Vulnerability in Windows 10 Version 1607
• How to Fix CVE-2026-2636: Cwe-159 improper handling of invalid use of special elements in Windows OS , Cwe-159 improper handling of invalid use of special elements in Windows OS
• How to Fix CVE-2026-20938: Path Traversal in Windows 11 version 22H3 , Path Traversal in Windows 11 version 22H3

Is CVE-2026-20945 actually being exploited?

According to the data sources above, no public confirmation of in-the-wild exploitation at this time. Either way, the fix is the same: apply the vendor patch.

Do I need to reboot after patching?

For OS or kernel updates, yes. For most userland packages a systemctl restart <service> is enough. Any process that loaded the old shared library keeps using it until restarted, so when in doubt, reboot.

What is the CVSS score?

4.6 (medium). Refer to the vendor advisory for the exact vector string.

Where is the official advisory?

See the References section at the bottom of this page; the vendor's URL is the authoritative source for affected builds and patched versions.

References

• Official vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20945
• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-20945

*Written by Sai Kiran Pandrala. Assembled from the official vendor advisory, NVD record, and CISA KEV listing on 2026-05-25. Always confirm against the vendor's advisory before applying changes in production.*