CVE-2020-26100
📋 TL;DR
CVE-2020-26100 is a Jailshell escape vulnerability in cPanel's chsh command that allows authenticated users to break out of restricted shell environments. This affects cPanel installations before version 88.0.3, potentially compromising shared hosting environments where users have Jailshell access.
💻 Affected Systems
- cPanel
📦 What is this software?
Cpanel by Cpanel
⚠️ Risk & Real-World Impact
Worst Case
An attacker gains full root access to the cPanel server, compromising all hosted accounts, data, and potentially other systems on the network.
Likely Case
Malicious users escape Jailshell restrictions to access other users' files, modify server configurations, or install malware.
If Mitigated
With proper access controls and monitoring, impact is limited to isolated incidents that can be quickly detected and contained.
🎯 Exploit Status
Requires authenticated access to a Jailshell account. Exploitation is straightforward once access is obtained.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 88.0.3
Vendor Advisory: https://docs.cpanel.net/changelogs/88-change-log/
Restart Required: No
Instructions:
1. Log into WHM as root. 2. Navigate to 'Update cPanel & WHM'. 3. Select 'Update to Latest Available Version'. 4. Confirm the update to version 88.0.3 or later.
🔧 Temporary Workarounds
Disable Jailshell
linuxTemporarily disable Jailshell for all users to prevent exploitation
whmapi1 set_tweaksetting key=jailshell value=0
🧯 If You Can't Patch
- Restrict Jailshell access to trusted users only through WHM security policies
- Implement strict monitoring of shell access logs and user activity
🔍 How to Verify
Check if Vulnerable:
Check cPanel version: cat /usr/local/cpanel/versionCheck Version:
cat /usr/local/cpanel/versionVerify Fix Applied:
Verify version is 88.0.3 or later: cat /usr/local/cpanel/version | grep -q '^88\.0\.[3-9]\|^8[9-9]\|^[9-9][0-9]' && echo 'Patched'📡 Detection & Monitoring
Log Indicators:
- Unusual chsh command usage in /var/log/secure
- Multiple failed shell escape attempts in system logs
Network Indicators:
- Unexpected outbound connections from cPanel server after user shell sessions
SIEM Query:
source="/var/log/secure" AND "chsh" AND ("jailshell" OR "escape")