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The article discusses CVE-2021-4034 (PwnKit), a privilege escalation vulnerability in Polkit’s pkexec, which had existed for over 13 years before discovery. Attackers exploited this flaw to gain root privileges on compromised Linux systems. The exploit leverages a memory corruption issue when pkexec improperly handles environment variables.
Reference:
The Tale of CVE-2021-4034 (PwnKit)
TryHackMe PwnKit Room
TryHackMe Polkit Room
You Should Know:
Detecting PwnKit Exploitation
Check for these forensic traces:
1. Review `.bash_history` of compromised users (e.g., `tomcat`):
cat /home/tomcat/.bash_history | grep -i "pwnkit|github|curl|wget"
- Check for Exploit Artifacts (common filenames like `PwnKit` or `pkexec` exploits):
find / -name "pwnkit" -o -name "pkexec" 2>/dev/null
3. Audit `pkexec` Usage (look for unusual executions):
grep -r "pkexec" /var/log/ 2>/dev/null
4. Check for Unauthorized Root Access:
lastlog | grep -v "Never logged in" grep -i "sudo|su" /var/log/auth.log
Exploitation & Mitigation Steps
Exploit Code (For Research Only)
A common PwnKit exploit involves:
gcc -o exploit exploit.c ./exploit
(Always verify exploit code before testing in isolated environments.)
Patch & Mitigation
1. Update `polkit` Immediately:
sudo apt update && sudo apt upgrade polkit -y
2. Remove SUID Bit from pkexec (Temporary Fix):
sudo chmod 0755 /usr/bin/pkexec
3. Monitor for Exploit Attempts:
auditctl -w /usr/bin/pkexec -p x -k pkexec_usage
Additional Threat Hunting Commands
- Check Running Processes for Anomalies:
ps aux | grep -i "pwnkit|exploit"
-
Inspect Network Connections:
netstat -tulnp | grep -i "unknown"
-
Verify File Integrity of
pkexec:rpm -Vf /usr/bin/pkexec For RPM-based systems dpkg -V polkit For Debian-based systems
What Undercode Say
PwnKit highlights the dangers of long-unpatched vulnerabilities in Linux privilege escalation mechanisms. Defenders must:
– Monitor `.bash_history` for suspicious downloads.
– Patch `polkit` immediately.
– Hunt for IOCs (e.g., GitHub-sourced exploit filenames).
– Use SELinux/AppArmor to restrict `pkexec` execution.
Always test exploits in controlled environments to understand attack patterns.
Expected Output:
[+] Vulnerable system detected: Check pkexec version [+] Exploit executed: Review /var/log/auth.log for root access [+] Mitigation applied: polkit updated to latest version
References:
Reported By: Stephan Berger – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
