CVE-2022-37393: Zimbra Privilege Escalation Vulnerability

CVE-2022-37393 Overview

CVE-2022-37393 is a local privilege escalation vulnerability in Zimbra Collaboration Suite that allows the zimbra user to escalate privileges to root through improper sudo configuration. The vulnerability exists because Zimbra's sudo configuration permits the zimbra user to execute the zmslapd binary as root with arbitrary parameters. As part of its intended functionality, zmslapd can load a user-defined configuration file, which includes plugins in the form of .so files that also execute with root privileges.

Critical Impact

An attacker who has gained access to the zimbra user account can leverage this misconfiguration to achieve full root access on the affected Zimbra server, potentially compromising all email data and using the server as a pivot point for further attacks.

Affected Products

• Zimbra Collaboration Suite 8.7.x (versions 8.7.6 through 8.7.11 including all patch levels)
• Zimbra Collaboration Suite 8.8.x (versions 8.8.0 through 8.8.15 including various patch levels up to p34)
• Zimbra Collaboration Suite 9.0.0 (versions p0 through p27)

Discovery Timeline

• August 16, 2022 - CVE CVE-2022-37393 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-37393

Vulnerability Analysis

This vulnerability represents a classic privilege escalation attack vector through insecure sudo configuration combined with the ability to load arbitrary shared objects. The Zimbra Collaboration Suite configures sudo to allow the zimbra service user to execute the zmslapd (Zimbra's OpenLDAP wrapper) binary with root privileges. The critical flaw is that arbitrary parameters can be passed to this binary.

The zmslapd binary inherently supports loading custom configuration files, and these configuration files can specify plugins as shared object (.so) files. Since the zmslapd process runs as root when invoked via sudo, any shared object loaded through the configuration file also executes with root privileges. This creates a straightforward path from the zimbra user to full root access.

Root Cause

The root cause is improper access control (CWE-284) in the sudo configuration for Zimbra. The sudoers entry grants overly permissive access, allowing the zimbra user to pass arbitrary arguments to the zmslapd binary. Combined with zmslapd's ability to load external plugins from user-specified configuration files, this creates a privilege escalation pathway. The configuration should have restricted the allowable parameters or prevented the loading of arbitrary configuration files when executed via sudo.

Attack Vector

The attack requires local access to the system as the zimbra user. An attacker who has compromised the Zimbra application or obtained credentials for the zimbra account can exploit this vulnerability through the following steps:

1. Create a malicious shared object file containing arbitrary code (e.g., spawning a root shell)
2. Craft a custom slapd configuration file that loads this malicious .so file as a plugin
3. Execute zmslapd via sudo with the custom configuration file specified as a parameter
4. The malicious shared object executes with root privileges

For detailed technical analysis, see the Rapid7 CVE-2022-37393 Analysis and the Zimbra Local Root Exploit writeup.

Detection Methods for CVE-2022-37393

Indicators of Compromise

• Unexpected .so files appearing in directories accessible to the zimbra user (particularly in /tmp, /var/zimbra, or home directories)
• Custom slapd.conf or .ldif configuration files in non-standard locations
• Process execution logs showing zmslapd being called with unusual -f (config file) parameters
• Evidence of sudo execution by the zimbra user outside normal operational patterns

Detection Strategies

• Monitor sudo logs (/var/log/auth.log or /var/log/secure) for zmslapd executions by the zimbra user with non-standard configuration file paths
• Implement file integrity monitoring on directories accessible to the zimbra user to detect creation of suspicious .so files
• Configure auditd rules to track executions of zmslapd with custom parameters
• Deploy behavioral detection for unexpected privilege escalation from the zimbra user context

Monitoring Recommendations

• Enable comprehensive logging for sudo operations and forward logs to a centralized SIEM
• Implement alerting on any new shared object files created by or accessible to the zimbra user
• Monitor for unusual process trees where zmslapd spawns unexpected child processes
• Review and audit the sudoers configuration regularly for overly permissive entries

How to Mitigate CVE-2022-37393

Immediate Actions Required

• Audit your current Zimbra sudo configuration to identify if the vulnerable sudoers entry exists
• Restrict sudo access for the zimbra user to only allow specific, hardcoded command parameters
• Implement additional access controls to limit which users can authenticate as the zimbra service account
• Monitor for any signs of compromise using the detection methods outlined above

Patch Information

Organizations should consult Zimbra's official security advisories and apply the latest patches for their respective Zimbra Collaboration Suite versions. A Metasploit module for this vulnerability has been developed, as documented in the GitHub Metasploit Pull Request, highlighting the importance of prompt remediation.

Workarounds

• Modify the sudoers configuration to remove or restrict the zimbra user's ability to pass arbitrary parameters to zmslapd
• Consider implementing sudo configuration that only allows execution with specific, pre-defined configuration files
• Apply principle of least privilege by reviewing all sudo entries for the zimbra user
• Implement mandatory access control (MAC) systems like SELinux or AppArmor to restrict the zimbra user's capabilities

# Example: Audit current sudo configuration for zimbra user
sudo grep -r "zimbra" /etc/sudoers /etc/sudoers.d/

# Example: Check for recently created .so files in common exploitation paths
find /tmp /var/zimbra /home -name "*.so" -mtime -7 -ls 2>/dev/null

# Example: Review sudo logs for suspicious zmslapd executions
grep "zmslapd" /var/log/auth.log | grep -v "standard-config-path"