⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Medium · CVSS 6.5 ⚠ ACTIVELY EXPLOITED — CISA KEV

How to Fix CVE-2019-5591: Information disclosure in Fortinet FortiOS

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

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityCVSS 6.5, Medium
Actively exploited?Yes, listed in CISA KEV (added 2021-11-03)
AffectedFortinet FortiOS (FortiOS 6.2.0 and below.)
Fixed inSee vendor advisory
Type (CWE)Information disclosure
⚠️ Patch immediately. CVE-2019-5591 is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03). Federal agencies had until 2022-05-03 to remediate.

What is CVE-2019-5591?

A Default Configuration vulnerability in FortiOS may allow an unauthenticated attacker on the same subnet to intercept sensitive information by impersonating the LDAP server.

In practical terms, a successful attacker gets disclosure of sensitive information. CISA has confirmed exploitation in the wild, so this is not a theoretical risk.

Am I affected?

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


get system status

How to fix CVE-2019-5591

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.

FortiOS / FortiGate (CLI)


# Vendor advisory: https://www.fortiguard.com/psirt/FG-IR-19-037
get system status
execute backup config tftp config-backup.conf 10.0.0.10
execute restore image tftp FGT_<patched-version>.out 10.0.0.10
# Device reboots automatically after image restore

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


# Vendor advisory: https://www.fortiguard.com/psirt/FG-IR-19-037
# Run as Administrator
$ErrorActionPreference = 'Stop'
$log = "$env:ProgramData\FortinetFortiOS-Patch-CVE-2019-5591.log"
function Write-Log($msg) { "$(Get-Date -Format s)  $msg" | Tee-Object -FilePath $log -Append }

Write-Log "Starting CVE-2019-5591 remediation for Fortinet Fortinet FortiOS"

# 1. Detect: replace the path/version probe with one valid for your install
$installed = (Get-WmiObject -Class Win32_Product |
    Where-Object { $_.Name -like '*Fortinet*' } |
    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\FortinetFortiOS-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\Fortinet\Fortinet FortiOS"
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\FortinetFortiOS-<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 { $_.Name -like '*Fortinet*' } |
    Select-Object -First 1 -ExpandProperty Version)
if ([version]$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://www.fortiguard.com/psirt/FG-IR-19-037
#!/usr/bin/env bash
set -euo pipefail
LOG=/var/log/fortinet-fortios-patch-cve-2019-5591.log
log()  { echo "$(date -Iseconds)  $*" | tee -a "$LOG"; }

log "Starting CVE-2019-5591 remediation for Fortinet Fortinet FortiOS"

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

# 2. Backup config
BACKUP=/var/backups/fortinet-fortios-$(date +%Y%m%d-%H%M)
mkdir -p "$BACKUP"
for d in /etc/fortinet-fortios /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 fortinet-fortios
else
    sudo dnf upgrade --security -y fortinet-fortios
fi

# 4. Verify
if [ "$PKG_MGR" = apt ]; then
    NEW=$(dpkg-query -W -f='${Version}' fortinet-fortios)
else
    NEW=$(rpm -q --queryformat '%{VERSION}' fortinet-fortios)
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.

No official vendor workaround is published for this CVE; patching is the only documented fix. The runnable hardening below is generic defense in depth, not a substitute for the patch.

Restrict the affected service to trusted networks (Linux):


# Vendor advisory: https://www.fortiguard.com/psirt/FG-IR-19-037
# Replace <port> with the affected service port and 10.0.0.0/24 with your admin subnet
sudo iptables -A INPUT -p tcp --dport <port> -s 10.0.0.0/24 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport <port> -j DROP

Windows Firewall equivalent:


# Vendor advisory: https://www.fortiguard.com/psirt/FG-IR-19-037
New-NetFirewallRule -DisplayName 'Allow affected service from admin subnet' \
    -Direction Inbound -Action Allow -Protocol TCP -LocalPort <port> -RemoteAddress 10.0.0.0/24
New-NetFirewallRule -DisplayName 'Block affected service from everywhere else' \
    -Direction Inbound -Action Block -Protocol TCP -LocalPort <port>

How to verify the fix worked

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


get system status

Expected output: a Version: FortiGate-... vthe patched build line (or higher build number).

Then re-run any vulnerability scanner you used previously and confirm the finding for CVE-2019-5591 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-2019-5591 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-2019-5591?

CVSS rates it 6.5 (Medium). Use that score to set your patch priority next to the other items in your queue.

Do I have to take Fortinet FortiOS 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-2019-5591 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

*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.*