CVE-2022-0824: Webmin RCE Vulnerability via Access Control

CVE-2022-0824 Overview

CVE-2022-0824 is an Improper Access Control vulnerability in Webmin that enables Remote Code Execution (RCE) in versions prior to 1.990. The vulnerability exists due to broken access control mechanisms that allow authenticated low-privileged users to bypass authorization checks and execute arbitrary commands on the underlying server with root privileges.

Critical Impact
Authenticated attackers can bypass access controls to achieve remote code execution on systems running vulnerable Webmin installations, potentially gaining complete server control.

Affected Products

Webmin versions prior to 1.990
Webmin File Manager module (affected versions)
Systems running Webmin web-based administration interface

Discovery Timeline

2022-03-02 - CVE CVE-2022-0824 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-0824

Vulnerability Analysis

This vulnerability stems from improper access control (CWE-284) and incorrect authorization (CWE-863) in Webmin's module access verification mechanism. The flaw allows authenticated users with limited privileges to bypass the access control checks that should restrict them from accessing certain administrative modules. When exploited successfully, an attacker with a low-privileged Webmin account can execute arbitrary commands on the server, typically with root-level privileges since Webmin commonly runs as root to perform system administration tasks.

The attack can be conducted remotely over the network without requiring any user interaction. Successful exploitation results in complete compromise of confidentiality, integrity, and availability of the target system.

Root Cause

The root cause lies in the web-lib-funcs.pl module's handling of foreign module access checks. The vulnerable code only checked for the presence of the FOREIGN_MODULE_NAME environment variable but failed to properly verify authorization when this variable was set. This allowed attackers to manipulate requests to bypass the normal access control checks that would otherwise prevent unauthorized module access.

Attack Vector

The attack is network-based and requires the attacker to have valid credentials for a low-privileged Webmin account. The attacker can then craft malicious requests that exploit the broken access control to access modules they should not have permission to use, ultimately achieving remote code execution. Public exploits are available through ExploitDB and Packet Storm, making this vulnerability particularly dangerous for unpatched systems.

perl

// Security patch in web-lib-funcs.pl - Foreign module access check fix
 	}
 
if ($module_name && !$main::no_acl_check &&
-    !defined($ENV{'FOREIGN_MODULE_NAME'}) &&
+    (!defined($ENV{'FOREIGN_MODULE_NAME'}) ||
+      defined($ENV{'FOREIGN_MODULE_SEC_CHECK'})) &&
     $main::webmin_script_type eq 'web') {
 	# Check if the HTTP user can access this module
 	if (!&foreign_available($module_name)) {

Source: GitHub Webmin Commit

The patch introduces an additional security check via the FOREIGN_MODULE_SEC_CHECK environment variable. The corrected logic ensures that access control verification is performed even when a foreign module name is defined, closing the bypass condition that allowed unauthorized access.

Detection Methods for CVE-2022-0824

Indicators of Compromise

Unusual access patterns to Webmin File Manager module from low-privileged accounts
Unexpected command execution or process spawning from the Webmin service
Log entries showing access to administrative modules by non-admin users
Suspicious HTTP requests targeting /file/show.cgi or similar File Manager endpoints

Detection Strategies

Monitor Webmin access logs for authorization bypass attempts and access to restricted modules
Implement network intrusion detection rules to identify known exploit patterns targeting Webmin
Review user account activity for low-privileged accounts attempting to access administrative functions
Deploy endpoint detection to identify suspicious process chains originating from Webmin

Monitoring Recommendations

Enable detailed logging in Webmin and forward logs to a centralized SIEM solution
Create alerts for any access to the File Manager module by users without explicit permissions
Monitor for outbound connections or reverse shells originating from the Webmin process
Track file system changes made by the Webmin service outside normal administrative operations

How to Mitigate CVE-2022-0824

Immediate Actions Required

Upgrade Webmin to version 1.990 or later immediately
Review all Webmin user accounts and remove unnecessary low-privileged accounts
Restrict network access to Webmin interface using firewall rules to trusted IP addresses only
Audit Webmin access logs for signs of previous exploitation attempts

Patch Information

Webmin has released version 1.990 which addresses this vulnerability. The fix is available in commit 39ea464f0c40b325decd6a5bfb7833fa4a142e38 on the official Webmin GitHub repository. Organizations should prioritize upgrading to the patched version as public exploits are widely available.

Workarounds

Disable the File Manager module if not required for operations
Implement network-level access controls to restrict Webmin access to trusted administrators only
Use a reverse proxy with additional authentication layers in front of Webmin
Consider temporarily disabling Webmin until patching can be completed if the risk is deemed critical

bash

# Restrict Webmin access to specific IP addresses using iptables
iptables -A INPUT -p tcp --dport 10000 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 10000 -j DROP

# Alternative: Disable Webmin service temporarily
systemctl stop webmin
systemctl disable webmin