How to Fix CVE-2017-8759: Remote Code Execution in Microsoft .NET Framework

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*By Sai Kiran Pandrala*

⚠️ Patch immediately. CVE-2017-8759 is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03). Federal agencies had until 2022-05-03 to remediate.

What is CVE-2017-8759?

Microsoft .NET Framework 2.0, 3.5, 3.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2 and 4.7 allow an attacker to execute code remotely via a malicious document or application, aka ".NET Framework Remote Code Execution Vulnerability."

In practical terms, a successful attacker gets remote code execution on the affected system. CISA has confirmed exploitation in the wild, so this is not a theoretical risk.

Am I affected?

You're affected if you run Microsoft Corporation Microsoft .NET Framework at any version in the Affected row above. Use these probes to find your installed build:

[System.Environment]::OSVersion.Version
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 10

How to fix CVE-2017-8759

The primary fix is to upgrade to the patched build listed in the Fixed in row above (See vendor advisory). Pick the platform that matches your install and run the commands below.

Linux (Ubuntu / Debian)

# Vendor advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2017-8759
sudo apt-get update
sudo apt-get install --only-upgrade microsoft--net-framework
# Confirm the installed version meets or exceeds <patched-version>
dpkg -s microsoft--net-framework | grep ^Version

Linux (RHEL / CentOS / Rocky)

sudo dnf upgrade --security microsoft--net-framework -y
rpm -q microsoft--net-framework

Windows (PowerShell, admin)

# Vendor advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2017-8759
# Try winget first
winget upgrade --id 'Microsoft Corporation.Microsoft .NET Framework' --silent --accept-source-agreements --accept-package-agreements
# If winget does not know the product, download the patched installer from the vendor and:
Start-Process -FilePath "$env:TEMP\MicrosoftNETFramework-<patched-version>.msi" -ArgumentList '/qn /norestart' -Wait

PowerShell script (Windows) - detect, back up, upgrade, verify, log

# Vendor advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2017-8759
# Run as Administrator
$ErrorActionPreference = 'Stop'
$log = "$env:ProgramData\MicrosoftNETFramework-Patch-CVE-2017-8759.log"
function Write-Log($msg) { "$(Get-Date -Format s)  $msg" | Tee-Object -FilePath $log -Append }

Write-Log "Starting CVE-2017-8759 remediation for Microsoft Corporation Microsoft .NET Framework"

# 1. Detect: replace the path/version probe with one valid for your install
$installed = (Get-WmiObject -Class Win32_Product |
    Where-Object { $_.Name -like '*Microsoft*' } |
    Select-Object -First 1 -ExpandProperty Version)
Write-Log "Detected version: $installed"

if (-not $installed) {
    Write-Log "Product not installed on this host; nothing to do."
    return
}
if ([version]$installed -ge [version]'<patched-version>') {
    Write-Log "Already at fixed version $installed; no action needed."
    return
}

# 2. Backup configuration to a timestamped folder
$backup = "$env:ProgramData\MicrosoftNETFramework-Backup-$(Get-Date -Format yyyyMMdd-HHmm)"
New-Item -ItemType Directory -Path $backup -Force | Out-Null
# Adjust the source path to match your install
$src = "$env:ProgramFiles\Microsoft Corporation\Microsoft .NET Framework"
if (Test-Path $src) { Copy-Item -Path $src -Destination $backup -Recurse -Force }
Write-Log "Backed up config to $backup"

# 3. Apply the patched installer (place the verified file on a share or staging path)
$installer = "$env:TEMP\MicrosoftNETFramework-<patched-version>.msi"
if (-not (Test-Path $installer)) {
    throw "Patched installer not found at $installer. Stage it from your software repo first."
}
Start-Process msiexec.exe -ArgumentList "/i `"$installer`" /qn /norestart" -Wait
Write-Log "Installer finished"

# 4. Verify
$verify = (Get-WmiObject -Class Win32_Product |
    Where-Object { $_.Name -like '*Microsoft*' } |
    Select-Object -First 1 -ExpandProperty Version)
if ([version]$verify -ge [version]'<patched-version>') {
    Write-Log "SUCCESS: now at $verify (>= <patched-version>)"
} else {
    Write-Log "FAILURE: still at $verify after install"
    exit 1
}

Bash script (Linux) - detect, back up, upgrade, verify, log

# Vendor advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2017-8759
#!/usr/bin/env bash
set -euo pipefail
LOG=/var/log/microsoft--net-framework-patch-cve-2017-8759.log
log()  { echo "$(date -Iseconds)  $*" | tee -a "$LOG"; }

log "Starting CVE-2017-8759 remediation for Microsoft Corporation Microsoft .NET Framework"

# 1. Detect installed version (works for deb and rpm packages)
if command -v dpkg >/dev/null && dpkg -s microsoft--net-framework >/dev/null 2>&1; then
    CURRENT=$(dpkg-query -W -f='${Version}' microsoft--net-framework)
    PKG_MGR=apt
elif command -v rpm >/dev/null && rpm -q microsoft--net-framework >/dev/null 2>&1; then
    CURRENT=$(rpm -q --queryformat '%{VERSION}' microsoft--net-framework)
    PKG_MGR=dnf
else
    log "microsoft--net-framework not installed via apt or rpm; check your package manager or vendor instructions."
    exit 0
fi
log "Detected: microsoft--net-framework=$CURRENT (manager=$PKG_MGR)"

# 2. Backup config
BACKUP=/var/backups/microsoft--net-framework-$(date +%Y%m%d-%H%M)
mkdir -p "$BACKUP"
for d in /etc/microsoft--net-framework /etc/${pkg%%-*} ; do
    [ -d "$d" ] && cp -a "$d" "$BACKUP/" && log "Backed up $d to $BACKUP"
done

# 3. Upgrade
if [ "$PKG_MGR" = apt ]; then
    sudo apt-get update -y
    sudo apt-get install --only-upgrade -y microsoft--net-framework
else
    sudo dnf upgrade --security -y microsoft--net-framework
fi

# 4. Verify
if [ "$PKG_MGR" = apt ]; then
    NEW=$(dpkg-query -W -f='${Version}' microsoft--net-framework)
else
    NEW=$(rpm -q --queryformat '%{VERSION}' microsoft--net-framework)
fi
log "After upgrade: $NEW"

# Optionally compare against <patched-version> with dpkg --compare-versions or sort -V
log "Done. Restart the affected service if the package install did not."

If you can't patch immediately

These are runnable hardening commands. They reduce blast radius but they're not a replacement for the vendor patch.

Rate-limit and log the affected endpoint at the reverse proxy

limit_req_zone $binary_remote_addr zone=admin:10m rate=10r/m;
location /<vulnerable-path> {
    limit_req zone=admin burst=5 nodelay;
    access_log /var/log/nginx/admin-access.log combined;
    proxy_pass http://backend;
}

How to verify the fix worked

Run the version probe again and confirm the running build matches the Fixed in row above.

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

Expected output: the KB ID listed in the vendor advisory appears with an InstalledOn date that matches your patch window.

Then re-run any vulnerability scanner you used previously and confirm the finding for CVE-2017-8759 has cleared. Sweep your logs for the indicators of compromise listed in the vendor or CISA advisory, especially if the system was internet-reachable during the disclosure window.

Frequently asked questions

Is CVE-2017-8759 being actively exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog, which means in-the-wild exploitation has been observed and confirmed.

How severe is CVE-2017-8759?

CVSS rates it 7.8 (High). Use that score to set your patch priority next to the other items in your queue.

Do I have to take Microsoft .NET Framework offline to apply the patch?

It depends on the deployment. High-availability or clustered installs can usually patch one node at a time with no full outage. Standalone installs typically need a short restart. Always follow the vendor's documented upgrade steps.

What if my vulnerability scanner still flags CVE-2017-8759 after I patch?

Re-run the scan after a service restart, then confirm the scanner's plugin set is up to date. Some scanners detect by banner version only and lag the official fix metadata by a release.

References

• Official vendor advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2017-8759
• NVD: https://nvd.nist.gov/vuln/detail/CVE-2017-8759
• CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• Additional reference: http://www.securityfocus.com/bid/100742
• Additional reference: https://github.com/bhdresh/CVE-2017-8759
• Additional reference: https://github.com/nccgroup/CVE-2017-8759

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