CVE-2020-15906: Tiki Wiki Auth Bypass Vulnerability

CVE-2020-15906 Overview

CVE-2020-15906 is a critical authentication bypass vulnerability in Tiki Wiki CMS Groupware. The vulnerability exists in tiki-login.php, which incorrectly sets the admin password to a blank value after 50 invalid login attempts. This flawed brute-force protection mechanism allows unauthenticated attackers to gain full administrative access to affected Tiki Wiki installations by simply triggering the lockout condition and then logging in with an empty password.

Critical Impact

Unauthenticated remote attackers can completely bypass authentication and gain full administrative control over Tiki Wiki CMS installations, potentially leading to complete system compromise, data theft, and website defacement.

Affected Products

• Tiki Wiki CMS Groupware versions prior to 21.2
• All Tiki versions since 16.3 that have not applied security patches

Discovery Timeline

• 2020-10-22 - CVE-2020-15906 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-15906

Vulnerability Analysis

This vulnerability is classified under CWE-307 (Improper Restriction of Excessive Authentication Attempts). The core issue lies in the flawed implementation of the brute-force protection mechanism within tiki-login.php. Instead of implementing a proper account lockout or rate-limiting strategy, the vulnerable code resets the administrator password to an empty string after detecting 50 failed login attempts.

This design flaw transforms what should be a protective security measure into a critical vulnerability. The intended purpose of tracking failed login attempts is to prevent brute-force attacks, but the implementation paradoxically creates a trivial authentication bypass. An attacker needs only to send 50 invalid login requests against the admin account, after which they can authenticate using a blank password.

The vulnerability is particularly severe because it requires no authentication to exploit and can be triggered entirely from the network. Once an attacker gains administrative access, they have complete control over the CMS, including the ability to modify content, access sensitive data, install malicious plugins, or pivot to attack the underlying server infrastructure.

Root Cause

The root cause is a critical logic error in the account lockout implementation within tiki-login.php. The developers intended to protect against brute-force attacks but implemented the protection mechanism incorrectly. After 50 failed authentication attempts, the system sets the admin user's password field to an empty value in the database, rather than locking the account or implementing a time-based delay. This allows subsequent login attempts with a blank password to succeed.

Attack Vector

The attack vector is network-based and requires no prior authentication or user interaction. An attacker can exploit this vulnerability by:

1. Identifying a vulnerable Tiki Wiki installation exposed to the network
2. Sending 50 failed login attempts against the admin account (or any targeted administrator account)
3. Waiting for the lockout mechanism to trigger, which resets the password to blank
4. Logging in with the admin username and an empty password
5. Gaining full administrative access to the Tiki Wiki CMS

This attack can be easily automated and executed remotely against any internet-facing Tiki Wiki installation running a vulnerable version. For detailed technical analysis, see the Packet Storm exploit documentation.

Detection Methods for CVE-2020-15906

Indicators of Compromise

• Unusual volume of failed login attempts (50+ in rapid succession) against admin accounts in tiki-login.php
• Successful admin login events following a series of failed authentication attempts
• Admin password hash field containing empty or null values in the users database table
• Unauthorized administrative actions or content modifications following suspicious login patterns

Detection Strategies

• Monitor web server access logs for repeated POST requests to tiki-login.php with high failure rates followed by successful authentication
• Implement intrusion detection rules to alert on 50+ failed login attempts from a single source IP within a short timeframe
• Configure database auditing to detect modifications to admin user password fields, particularly when set to empty values
• Deploy web application firewall (WAF) rules to detect and block brute-force login patterns targeting Tiki Wiki installations

Monitoring Recommendations

• Enable verbose logging for authentication events in Tiki Wiki and forward logs to a SIEM solution
• Set up real-time alerting for authentication anomalies, including password reset events and unusual login patterns
• Regularly audit administrator accounts for password integrity and unexpected modifications
• Monitor for network reconnaissance activity targeting CMS login pages

How to Mitigate CVE-2020-15906

Immediate Actions Required

• Upgrade Tiki Wiki CMS to version 21.2 or later immediately
• Verify admin account password integrity and reset to a strong password if compromise is suspected
• Review access logs for signs of exploitation and investigate any suspicious authentication patterns
• Consider temporarily restricting access to tiki-login.php via IP allowlisting or taking the application offline until patched

Patch Information

Tiki has released security patches addressing this vulnerability for all supported versions since 16.3. Organizations should upgrade to Tiki version 21.2 or later, which contains the fix for CVE-2020-15906. For detailed patch information and download links, refer to the Tiki Security Release Overview.

Workarounds

• Implement a web application firewall (WAF) rule to block requests after detecting more than 10-20 failed login attempts from a single IP
• Restrict access to tiki-login.php by IP address to limit exposure to trusted administrative networks only
• Enable multi-factor authentication (MFA) if supported by your Tiki Wiki version to add an additional authentication layer
• Consider placing the Tiki Wiki installation behind a VPN or reverse proxy with additional authentication requirements

# Example Apache .htaccess configuration to restrict admin login access
<Files "tiki-login.php">
    Order Deny,Allow
    Deny from all
    Allow from 192.168.1.0/24
    Allow from 10.0.0.0/8
</Files>