⚠ 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-2020-36193: Improper Link Resolution Before File Access ('Link Following') in Archive Tar

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

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityCVSS 7.5 - High
Actively exploited?Yes, listed in CISA KEV (added 2022-08-25)
Affectedn/a: n/a
Fixed inSee vendor advisory for the patched build
Type (CWE)CWE-59 Improper Link Resolution Before File Access ('Link Following')
Patch immediately. CISA's Known Exploited Vulnerabilities catalog lists this CVE, which means active exploitation has been confirmed. CISA KEV entry added 2022-08-25, federal due date 2022-09-15.

What is CVE-2020-36193?

CVE-2020-36193 is a improper link resolution before file access ('link following') in Archive Tar from Pear. Tar.php in Archive_Tar through 1.4.11 allows write operations with Directory Traversal due to inadequate checking of symbolic links, a related issue to CVE-2020-28948.

Why this CVE matters

This CVE sits on CISA's Known Exploited Vulnerabilities catalog, which only happens after active exploitation is observed in the wild. The improper link resolution before file access ('link following') class of flaw gives attackers a reliable foothold against vulnerable instances of Archive Tar. If your deployment matches the affected versions, treat any window of unpatched exposure as compromise-likely and review logs accordingly.

Am I affected?

Run the version check that matches your platform. If the installed build sits inside the affected range from the table above, the fix applies to you.


# Linux package check
dpkg -s php 2>/dev/null | grep -i version    # Debian / Ubuntu
rpm -q php 2>/dev/null                       # RHEL / Rocky

How to fix CVE-2020-36193

Apply the patched build the vendor names in the advisory. The commands below are starting points keyed to common platforms - adapt the package name and target version to your environment.

Ubuntu / Debian


sudo apt-get update
sudo apt-get install --only-upgrade php
# verify the package version matches the fixed release in the advisory
dpkg -s php | grep -i version

RHEL / CentOS / Rocky / AlmaLinux


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

Container image


# Vendor advisory: https://www.drupal.org/sa-core-2021-001
# Pull the patched base image and rebuild
docker pull <your-registry>/php:<patched-tag>
docker build -t <your-app>:patched .
docker stop <your-app> && docker rm <your-app>
docker run -d --name <your-app> <your-app>:patched

PowerShell detect/upgrade/verify/log (Windows)


# CVE-2020-36193 remediation runner — adapt the version checks to your environment.
$log = "C:\Logs\CVE-2020-36193-fix.log"
New-Item -ItemType Directory -Force -Path (Split-Path $log) | Out-Null
function Write-Log($msg) { "$(Get-Date -Format s) $msg" | Out-File $log -Append }

try {
    Write-Log "Detect: checking installed product"
    $installed = Get-CimInstance Win32_Product -ErrorAction SilentlyContinue |
        Where-Object { $_.Name -match 'product' }
    if (-not $installed) { Write-Log "Product not installed; nothing to do"; return }
    Write-Log "Found version $($installed.Version)"

    Write-Log "Backup: copying program files and registry hive"
    $stamp = Get-Date -Format yyyyMMdd-HHmm
    $backup = "C:\Backup\CVE-2020-36193-$stamp"
    New-Item -ItemType Directory -Force -Path $backup | Out-Null
    Copy-Item $installed.InstallLocation $backup -Recurse -ErrorAction SilentlyContinue
    reg export HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall "$backup\uninstall.reg" /y | Out-Null

    Write-Log "Upgrade: install patched build via vendor MSI / Windows Update"
    # Example MSI:  Start-Process msiexec.exe -ArgumentList '/i C:\Patches\product-patched.msi /qn /norestart' -Wait
    Install-WindowsUpdate -AcceptAll -AutoReboot -ErrorAction SilentlyContinue

    Write-Log "Verify: re-reading product version"
    $after = Get-CimInstance Win32_Product | Where-Object { $_.Name -match 'product' }
    Write-Log "Post-patch version: $($after.Version)"
    if ($after.Version -ne $installed.Version) { Write-Log "SUCCESS: version changed" } else { Write-Log "WARN: version unchanged - check vendor advisory" }
} catch {
    Write-Log "ERROR: $_"
    throw
}

Bash detect/upgrade/verify/log (Linux)


#!/usr/bin/env bash
# CVE-2020-36193 remediation runner. Re-runnable, exits non-zero on failure.
set -euo pipefail
log() { printf '%s %s\n' "$(date -Is)" "$*" | tee -a /var/log/cve-2020-36193-fix.log; }

log "Detect: current php version"
if command -v dpkg >/dev/null 2>&1; then
    current=$(dpkg-query -W -f='${Version}' php 2>/dev/null || echo "not-installed")
elif command -v rpm >/dev/null 2>&1; then
    current=$(rpm -q --qf '%{VERSION}-%{RELEASE}' php 2>/dev/null || echo "not-installed")
else
    current="unknown"
fi
log "Current: $current"

log "Backup: snapshotting config"
backup="/var/backups/cve-2020-36193-$(date +%Y%m%d-%H%M)"
mkdir -p "$backup"
[ -d /etc/php ] && cp -a /etc/php "$backup/" || true

log "Upgrade: applying vendor patch"
if command -v apt-get >/dev/null 2>&1; then
    sudo apt-get update -qq
    sudo apt-get install -y --only-upgrade php
elif command -v dnf >/dev/null 2>&1; then
    sudo dnf upgrade -y php
elif command -v yum >/dev/null 2>&1; then
    sudo yum update -y php
fi

log "Verify: re-reading php version"
if command -v dpkg >/dev/null 2>&1; then
    after=$(dpkg-query -W -f='${Version}' php)
else
    after=$(rpm -q --qf '%{VERSION}-%{RELEASE}' php)
fi
log "After: $after"

if [ "$after" != "$current" ]; then
    log "SUCCESS: php upgraded"
else
    log "WARN: version unchanged. Confirm the patched build is in your repository."
    exit 1
fi

After the upgrade, restart any service that loads the patched binary so the new code is actually running.

If you can't patch immediately

Patching is the only durable fix. These mitigations cut exposure while the change window is scheduled, they do not remove the vulnerability.

Web server / WAF rule (ModSecurity sample)


# Append to /etc/modsecurity/rules/local.conf and reload Apache.
SecRule REQUEST_URI "@rx (?:\.\./|%2e%2e/)" \
    "id:900001,phase:1,deny,status:403,msg:'Path traversal attempt blocked'"
SecRule ARGS "@rx (?:union[\s/*]+select|select[\s/*]+.*from)" \
    "id:900002,phase:2,deny,status:403,msg:'SQLi pattern blocked'"


sudo systemctl reload apache2    # or nginx

How to verify the fix worked

After applying the patched build, confirm the version string matches the fixed release named in the Pear advisory.


dpkg -s php | grep -i version       # Debian / Ubuntu
rpm -q php                          # RHEL / Rocky

Run an authenticated vulnerability scan with a current signature set and confirm the scanner no longer flags CVE-2020-36193. For internet-facing deployments that were unpatched during the disclosure window, review logs for the affected endpoints over the full exposure period and rotate any credentials the vulnerable process could touch.

Frequently asked questions

Is CVE-2020-36193 being exploited in the wild?

Yes. CISA added CVE-2020-36193 to the Known Exploited Vulnerabilities catalog, which means active exploitation has been confirmed.

Will a firewall rule or WAF signature fully mitigate CVE-2020-36193?

No. Network-layer filters slow opportunistic scanners and block a subset of payloads, but a focused attacker who knows the bug will work around them. The vendor patch is the only durable fix.

Do I need to assume compromise if the affected service was internet-facing and unpatched?

For a CVE that CISA confirms is under active exploitation, yes. Review logs for the affected endpoints over the entire exposure window, rotate credentials the vulnerable process could read, and look for unexpected accounts, scheduled tasks, or outbound connections.

References

*This guide was assembled from the official vendor advisory, the NVD record, and the CISA KEV catalog entry on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*