Access Control Lists

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  1. Access Control Lists (ACLs)

Access Control Lists (ACLs) are a fundamental security feature in MediaWiki, controlling which users or groups of users have permission to perform specific actions on pages, files, and other wiki elements. Understanding ACLs is crucial for maintaining the integrity, security, and collaborative nature of a MediaWiki installation, especially as it grows and attracts more contributors. This article aims to provide a comprehensive introduction to ACLs for beginners, covering their concepts, implementation, and common use cases.

What are Access Control Lists?

At their core, ACLs are lists of permissions attached to a wiki object (like a page or a file) that specify which users or groups are granted or denied access to that object. Think of it like a bouncer at a club – the ACL is the list of who's allowed inside and what they're allowed to do.

In MediaWiki, ACLs aren't directly visible as a single "ACL" file. Instead, they are managed through the Permissions system, which utilizes various rights groups and user-specific exceptions to achieve access control. The system relies heavily on the underlying database to store and enforce these rules.

The basic principle is that permissions are *inherited*. If a user is a member of a group with certain permissions, they inherit those permissions. However, these inherited permissions can be overridden by explicitly granting or denying permissions to the user directly. This allows for a flexible and granular level of control.

Key Concepts

Before diving into implementation, let’s define some important concepts:

  • **Principals:** These are the entities requesting access. In MediaWiki, principals can be:
   *   **Users:** Individual registered users of the wiki.
   *   **Groups:** Collections of users, defined by role or function (e.g., administrators, editors, autoconfirmed users).  User groups are a critical component of ACL management.
  • **Resources:** These are the wiki objects being accessed. Examples include:
   *   **Pages:**  The main content of the wiki.
   *   **Files:** Images, documents, and other uploaded media.
   *   **Namespaces:**  Categorical divisions of the wiki (e.g., Main, Talk, File).
   *   **Special Pages:** System-defined pages for administration and functionality.
  • **Permissions (Rights):** These define the actions that can be performed on a resource. Common permissions include:
   *   `read`:  View the page or file.
   *   `edit`:  Modify the page content.
   *   `create`:  Create new pages (often restricted to certain namespaces).
   *   `delete`:  Remove pages or files.
   *   `move`:  Rename or move pages.
   *   `upload`: Upload files.
   *   `block`: Block users from editing.
   *   `protect`: Protect pages from editing.
   *   `unprotect`: Remove protection from pages.
  • **Explicit Permissions:** Permissions directly assigned to a user or group for a specific resource.
  • **Implicit Permissions:** Permissions inherited from group membership.
  • **Deny vs. Allow:** ACLs can explicitly *allow* access or *deny* access. Deny generally takes precedence over allow. MediaWiki largely operates on the "allow by default" principle, meaning users can generally do things unless explicitly prevented.

How ACLs Work in MediaWiki

MediaWiki doesn’t have a direct “ACL editor” in the traditional sense. Permissions are managed through a combination of:

1. **User Rights Management:** Administrators assign users to predefined user groups (e.g., `sysop`, `editor`, `autoconfirmed`). These groups have associated rights defined in the `UserRightsDefinitions.php` file located in the `includes/` directory of your MediaWiki installation. This file defines which rights are assigned to each group. Editing this file requires careful consideration and understanding of the consequences. See Manual:User rights management for details. 2. **Page Protection:** Administrators can protect pages at various levels: 

   *   **Fully Protected:** Only administrators can edit the page.
   *   **Semi-Protected:** Only autoconfirmed users can edit the page.
   *   **Template Protected:** Primarily for templates, restricting editing to administrators and template editors.
   *   **Cascading Protection:** Protects all included templates and pages.

3. **Namespace Permissions:** Certain namespaces (like the `MediaWiki:` namespace) might have restricted editing rights. 4. **Individual User Permissions:** Administrators can grant or revoke specific rights from individual users, overriding their group memberships. This is done through the Special:UserRights page. 5. **Extension-Based ACLs:** Extensions like Extension:AccessControl provide more advanced and granular ACL management capabilities, allowing for custom permissions and rules. This is useful for complex scenarios requiring fine-grained control. 6. **IP Address Blocking:** While not strictly an ACL, blocking specific IP addresses or ranges effectively denies access to the wiki. See Manual:Blocking IP addresses.

Common Use Cases

  • **Restricting Editing to Administrators:** Fully protecting critical system pages (e.g., `Main Page`, `MediaWiki:Common.js`) ensures that only administrators can modify them, preventing accidental or malicious changes.
  • **Controlling Content Creation:** Restricting the `create` right in certain namespaces (e.g., `Project:`) can prevent users from creating unnecessary or inappropriate pages.
  • **Managing Sensitive Information:** Protecting pages containing confidential data (e.g., user lists, internal policies) limits access to authorized personnel.
  • **Preventing Vandalism:** Semi-protecting frequently vandalized pages reduces the risk of damage by requiring users to be autoconfirmed before editing.
  • **Collaboration Control:** Granting specific editing rights to a group of users for a particular project allows for controlled collaboration on a specific set of pages.
  • **File Upload Restrictions:** Limiting the `upload` right prevents unauthorized users from uploading potentially harmful or irrelevant files.
  • **Moderation:** Granting `delete` rights to moderators allows them to remove inappropriate content.
  • **Template Management:** Protecting templates prevents accidental breakage of numerous pages that rely on them.

Implementing ACLs: A Step-by-Step Example

Let's say you want to restrict editing of the "Project:Internal Documents" page to members of the "InternalTeam" user group.

1. **Create the User Group:** If the "InternalTeam" group doesn't exist, you'll need to create it. This requires editing the `LocalSettings.php` file. Add a line similar to this: 

   ```php
   $wgGroups[] = 'InternalTeam';
   ```

   After adding this line, clear the MediaWiki cache.

2. **Assign Users to the Group:** Log in as an administrator and navigate to Special:UserRights. Find the users you want to add to the "InternalTeam" group and assign them to it. 3. **Protect the Page:** Navigate to "Project:Internal Documents". Click the "Protect" tab. Select "Semi-protected" or "Fully protected" depending on your desired level of restriction. Choose the "Only administrators and users in the 'InternalTeam' group can edit this page" option (or similar, depending on your MediaWiki version). Save the protection settings.

Now, only administrators and users who are members of the "InternalTeam" group will be able to edit the "Project:Internal Documents" page.

Troubleshooting ACL Issues

  • **Permissions Not Applying:** Ensure the user is logged in. Clear the browser cache. Verify the user is correctly assigned to the appropriate group. Check the page protection settings. Clear the MediaWiki cache.
  • **Unexpected Access:** Review the user's group memberships and individual permissions. Check for any conflicting permissions. Examine the page protection settings.
  • **Group Rights Not Defined:** Verify the group is defined in `UserRightsDefinitions.php` and that it has the necessary rights assigned.
  • **Caching Issues:** MediaWiki aggressively caches permissions. Always clear the cache after making changes to user rights or page protection settings. Use `$wgMainCacheType = 'database';` in LocalSettings.php for more reliable caching.
  • **Extension Conflicts:** If you're using extensions, ensure they aren't interfering with the default ACL system.

Advanced Considerations

  • **Regularly Review Permissions:** Periodically audit user rights and page protection settings to ensure they remain appropriate and secure.
  • **Principle of Least Privilege:** Grant users only the minimum necessary permissions to perform their tasks.
  • **Documentation:** Maintain clear documentation of your wiki's ACL policies and procedures.
  • **Automation:** Consider using scripts or extensions to automate the management of user rights and page protection.
  • **LDAP Integration:** Integrate MediaWiki with Lightweight Directory Access Protocol (LDAP) for centralized user management and authentication. See Manual:LDAP authentication.
  • **Rate Limiting:** Implement rate limiting to prevent brute-force attacks and excessive editing. Consider using extensions like Extension:AbusePrevention.
  • **CAPTCHA:** Use CAPTCHAs for actions like creating accounts or editing sensitive pages to prevent automated abuse. See Manual:Captcha/Configuration.
  • **Two-Factor Authentication (2FA):** Enable 2FA to add an extra layer of security to user accounts. Consider using extensions like Extension:TwoFactorAuth.
  • **Security Audits:** Conduct regular security audits to identify and address potential vulnerabilities in your wiki's ACL configuration.

Resources and Further Reading

Manual:Configuration Manual:FAQ Manual:Upgrading Extension point API:Main page MediaWiki Help:Contents Special:AllMessages Manual:Shortcuts Manual:Talk pages

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