CVE-2021-29741
📋 TL;DR
This vulnerability in IBM AIX and VIOS allows a local user to exploit a flaw in Korn Shell (ksh) to escalate privileges to root. It affects IBM AIX 7.1, 7.2, and VIOS 3.1 systems. Attackers must have local access to the system to exploit this vulnerability.
💻 Affected Systems
- IBM AIX
- IBM VIOS
📦 What is this software?
Aix by Ibm
Aix by Ibm
⚠️ Risk & Real-World Impact
Worst Case
Local attacker gains full root privileges, enabling complete system compromise, data theft, persistence establishment, and lateral movement.
Likely Case
Privileged local user or attacker with initial access escalates to root to install malware, steal credentials, or pivot to other systems.
If Mitigated
With proper access controls and monitoring, exploitation attempts are detected and contained before significant damage occurs.
🎯 Exploit Status
Requires local access and some user privileges to exploit. No public exploit code available as per IBM advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: AIX: APAR IJ29860; VIOS: APAR IJ29861
Vendor Advisory: https://www.ibm.com/support/pages/node/6477018
Restart Required: Yes
Instructions:
1. Download appropriate APAR from IBM Fix Central. 2. Apply interim fix using smitty or installp command. 3. Reboot system to ensure patch is fully applied.
🔧 Temporary Workarounds
Restrict ksh usage
aixLimit Korn Shell usage to trusted users only and monitor for suspicious ksh activity.
chmod 750 /usr/bin/ksh
chown root:system /usr/bin/ksh
🧯 If You Can't Patch
- Implement strict access controls to limit who can execute ksh and monitor for privilege escalation attempts.
- Use security monitoring tools to detect unusual ksh process activity and privilege changes.
🔍 How to Verify
Check if Vulnerable:
Check if system is running AIX 7.1, 7.2 or VIOS 3.1 without the APAR applied: oslevel -sCheck Version:
oslevel -sVerify Fix Applied:
Verify APAR IJ29860 (AIX) or IJ29861 (VIOS) is installed: instfix -i | grep IJ29860📡 Detection & Monitoring
Log Indicators:
- Unexpected privilege escalation via ksh processes
- Root shell spawned from non-root user sessions
- Failed ksh execution attempts
Network Indicators:
- N/A - local exploitation only
SIEM Query:
Process creation where parent process contains 'ksh' and user transitions from non-root to root