How to Fix CVE-2017-9841: Code injection in PHP

WARNING: This vulnerability is on the CISA Known Exploited Vulnerabilities catalog (added 2022-02-15). Federal civilian agencies must remediate by 2022-08-15. Treat it as active exploitation, not theoretical.

What is CVE-2017-9841?

Util/PHP/eval-stdin.php in PHPUnit before 4.8.28 and 5.x before 5.6.3 allows remote attackers to execute arbitrary PHP code via HTTP POST data beginning with a "<?php " substring, as demonstrated by an attack on a site with an exposed /vendor folder, i.e., external access to the /vendor/phpunit/phpunit/src/Util/PHP/eval-stdin.php URI.

Spot the symptom

Run the version check that matches your platform:

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

Compare what you see against the Affected row above (See the vendor advisory linked below). If your build sits inside that range, you are exposed and should patch.

How to fix CVE-2017-9841

The primary fix is to upgrade PHP 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 php
php --version 2>/dev/null || dpkg -s php | grep -i version

RHEL / CentOS / Rocky / AlmaLinux

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

SUSE / openSUSE

sudo zypper patch --category security
rpm -q php

Complete PowerShell remediation script (Windows)

# Fix script for CVE-2017-9841 affecting PHP
# Run as administrator. Detect -> backup -> upgrade -> verify -> log.

$ErrorActionPreference = "Stop"
$LogPath  = "C:\Logs\CVE-2017-9841-fix-$(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 PHP"
    $pkg = winget list --id "PHP" 2>$null
    Write-Host $pkg

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

    Write-Host "[3/4] Applying upgrade to latest"
    winget upgrade --id "PHP" --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 "PHP"
    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-2017-9841 affecting PHP
# Detect -> backup -> upgrade -> verify -> log.

set -euo pipefail
LOG="/var/log/cve-2017-9841-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 php 2>/dev/null | grep -i version || echo "php not installed via dpkg"
elif command -v rpm >/dev/null; then
    rpm -q php || echo "php not installed via rpm"
fi

echo "[2/4] Backing up configuration"
BACKUP="/root/backup-cve-2017-9841-$(date +%Y%m%d)"
mkdir -p "$BACKUP"
for d in /etc/php /etc/php.d /etc/php.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 php
elif command -v dnf >/dev/null; then
    dnf upgrade --security -y php
elif command -v yum >/dev/null; then
    yum update -y php
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 php 2>/dev/null | grep -i version
elif command -v rpm >/dev/null; then
    rpm -q php
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

Reduce attack surface

# php is a library or shell, not a service. Restart any daemon that links it
# after applying the patch so the new code is actually loaded in memory.
sudo lsof | grep php | awk '{print $1, $2}' | sort -u
# Then restart each listed process group, or schedule a reboot at the next window.

Full fix path

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

# Windows
winget list | findstr /I "php"
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.

Is CVE-2017-9841 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?

9.8 (critical). 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://security.gentoo.org/glsa/201711-15
• NVD: https://nvd.nist.gov/vuln/detail/CVE-2017-9841
• CISA KEV catalog entry: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• http://www.securityfocus.com/bid/101798
• http://www.securitytracker.com/id/1039812
• https://www.oracle.com/security-alerts/cpuoct2021.html
• https://github.com/sebastianbergmann/phpunit/commit/284a69fb88a2d0845d23f42974a583d8f59bf5a5

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

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