⚠ 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 7.5 ⚠ ACTIVELY EXPLOITED — CISA KEV

How to Fix CVE-2019-17558: Neutralization of special elements in output in Apache Solr

⚡ At a glance
Severity7.5 (High)
Actively exploited?Yes, listed in CISA KEV (added 2021-11-03)
AffectedApache Solr Apache Solr 5.0.0 to Apache Solr 8.3.1
Fixed inSee vendor advisory
Type (CWE)CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
WARNING: This vulnerability is on the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03). Federal civilian agencies must remediate by 2022-05-03. Treat it as active exploitation, not theoretical.

What is CVE-2019-17558?

Apache Solr 5.0.0 to Apache Solr 8.3.1 are vulnerable to a Remote Code Execution through the VelocityResponseWriter. A Velocity template can be provided through Velocity templates in a configset velocity/ directory or as a parameter. A user defined configset could contain renderable, potentially malicious, templates. Parameter provided templates are disabled by default, but can be enabled by setting params.resource.loader.enabled by defining a response writer with that setting set to true.

Am I affected?

Run the version check that matches your platform:


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

Compare what you see against the Affected row above (Apache Solr Apache Solr 5.0.0 to Apache Solr 8.3.1). If your build sits inside that range, you are exposed and should patch.

How to fix CVE-2019-17558

The primary fix is to upgrade Apache Solr to the patched build. Use the commands for your platform below; the patched version listed in the vendor advisory is: See vendor advisory.

Ubuntu / Debian


sudo apt-get update
sudo apt-get install --only-upgrade solr
solr --version 2>/dev/null || dpkg -s solr | grep -i version

RHEL / CentOS / Rocky / AlmaLinux


sudo dnf upgrade --security solr -y
rpm -q solr

SUSE / openSUSE


sudo zypper patch --category security
rpm -q solr

Complete PowerShell remediation script (Windows)


# Fix script for CVE-2019-17558 affecting Apache Solr
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2019-17558-fix-$(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 Apache Solr"
    $pkg = winget list --id "Apache_Solr" 2>$null
    Write-Host $pkg

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

    Write-Host "[3/4] Applying upgrade to latest"
    winget upgrade --id "Apache_Solr" --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 "Apache_Solr"
    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-2019-17558 affecting Apache Solr
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2019-17558-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 solr 2>/dev/null | grep -i version || echo "solr not installed via dpkg"
elif command -v rpm >/dev/null; then
    rpm -q solr || echo "solr not installed via rpm"
fi

echo "[2/4] Backing up configuration"
BACKUP="/root/backup-cve-2019-17558-$(date +%Y%m%d)"
mkdir -p "$BACKUP"
for d in /etc/solr /etc/solr.d /etc/solr.conf; do
    [ -e "$d" ] && cp -a "$d" "$BACKUP/" || true
done

echo "[3/4] Applying upgrade (target: latest)"
if command -v apt-get >/dev/null; then
    apt-get update
    apt-get install --only-upgrade -y solr
elif command -v dnf >/dev/null; then
    dnf upgrade --security -y solr
elif command -v yum >/dev/null; then
    yum update -y solr
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 solr 2>/dev/null | grep -i version
elif command -v rpm >/dev/null; then
    rpm -q solr
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.

Network restriction (Linux, nftables)


# Block inbound traffic to the affected service from untrusted networks
sudo nft add table inet filter
sudo nft 'add chain inet filter input { type filter hook input priority 0 ; }'
sudo nft 'add rule inet filter input tcp dport {443, 80} ip saddr != 10.0.0.0/8 drop'
sudo nft list ruleset

Service-level fallback


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

How to verify the fix worked


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


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

Expected: the reported version is at or above the patched build documented in the advisory. 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

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

Is CVE-2019-17558 actually being exploited?

According to the data sources above, yes, CISA has it listed as actively exploited. 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?

7.5 (high). 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

*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.*