CVE-2022-0829: Webmin Auth Bypass Vulnerability

CVE-2022-0829 Overview

CVE-2022-0829 is an Improper Authorization vulnerability affecting Webmin, a popular web-based system administration tool for Unix-like systems. This vulnerability exists in versions prior to 1.990 and allows authenticated attackers to bypass access controls, potentially leading to unauthorized modifications and denial of service conditions.

Critical Impact

Authenticated attackers can bypass authorization checks to perform privileged operations, potentially leading to unauthorized system modifications and denial of service.

Affected Products

• Webmin versions prior to 1.990
• All platforms running vulnerable Webmin installations

Discovery Timeline

• 2022-03-02 - CVE-2022-0829 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-0829

Vulnerability Analysis

This vulnerability stems from missing authorization checks in the Webmin cron module, specifically within the save_allow.cgi script. The flaw allows authenticated users with limited privileges to access functionality that should be restricted to administrators only. When exploited, an attacker can manipulate cron user permissions without proper authorization verification, leading to potential system integrity compromise and denial of service conditions.

The vulnerability is classified under CWE-285 (Improper Authorization) and CWE-863 (Incorrect Authorization), indicating a fundamental access control weakness in how Webmin validates user permissions before executing privileged operations.

Root Cause

The root cause of CVE-2022-0829 is a missing permissions check in the cron/save_allow.cgi file. The code path that handles saving allowed cron users failed to verify that the requesting user had the necessary allow permission before processing the request. This broken access control allowed any authenticated user to modify cron access lists regardless of their assigned role.

Attack Vector

The attack is network-based and requires the attacker to have low-privileged authentication to the Webmin interface. Once authenticated, the attacker can directly access the vulnerable endpoint to bypass authorization controls. No user interaction is required beyond the initial attack setup. The vulnerability enables unauthorized modification of cron configurations and can result in denial of service through manipulation of system job scheduling.

 
 require './cron-lib.pl';
 &ReadParse();
+$access{'allow'} || &error($text{'allow_ecannot'});
 
 &lock_file($config{cron_allow_file});
 &lock_file($config{cron_deny_file});

Source: GitHub Commit Update

The patch adds a critical authorization check ($access{'allow'}) that verifies the user has the allow permission before proceeding with the file operations. Without this check, any authenticated user could lock and modify the cron allow/deny files.

Detection Methods for CVE-2022-0829

Indicators of Compromise

• Unexpected access to /cron/save_allow.cgi by non-administrative users in Webmin access logs
• Unauthorized modifications to cron allow or deny files (cron.allow, cron.deny)
• Anomalous cron job scheduling activities following unauthorized configuration changes

Detection Strategies

• Monitor Webmin access logs for requests to save_allow.cgi from users without administrative privileges
• Implement file integrity monitoring on cron configuration files to detect unauthorized changes
• Deploy web application firewall rules to alert on suspicious parameter patterns in cron module requests

Monitoring Recommendations

• Enable detailed access logging in Webmin and forward logs to a SIEM for centralized analysis
• Configure alerts for any access to cron management endpoints by non-admin users
• Regularly audit Webmin user permissions and access control configurations

How to Mitigate CVE-2022-0829

Immediate Actions Required

• Upgrade Webmin to version 1.990 or later immediately
• Review Webmin access logs for evidence of exploitation attempts
• Audit cron configuration files for unauthorized modifications
• Restrict Webmin network access to trusted management networks only

Patch Information

The vulnerability has been addressed in Webmin version 1.990. The fix adds proper authorization validation by checking the $access{'allow'} permission before processing requests to modify cron user permissions. Organizations should apply this update through their standard patch management process. The specific fix can be reviewed in the GitHub commit.

Workarounds

• Disable the cron module in Webmin if not required for operations
• Implement network-level access controls to restrict Webmin access to trusted administrator IP addresses
• Use a reverse proxy with additional authentication layers to protect the Webmin interface

# Restrict Webmin access to specific IP addresses via 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