Extension:CheckUser

For the Wikimedia Foundation CheckUser policy, see CheckUser policy.''

CheckUser is an extension that allows a user (with the checkuser permission) to check which IPs are used by a given username and which usernames are used by a given IP, without having to run queries directly against the database by hand. The extension is running live on all Wikimedia wikis.

Installation
The extension is released under the GNU General Public License 2.0 or later. The software is provided as-is. Updates will be made according to the needs of Wikimedia wikis; or where critical vulnerabilities are discovered.

Basic

 * If you have installed other extensions without running, run that first.

Installing without command prompt access
Many hosting providers don't allow direct shell access, but allow creation of cron jobs (e.g. via cPanel web interface). For those hosting providers a temporary cron job can be used to run  ( naturally /path/to should be replaced with real full path to install.php). If you are using a remote server and do not have command prompt access (nor cron job solution is suitable for you), but do have access through phpMyAdmin, substitute these steps for step #2 above:


 * 1) Download and
 * 2) In phpMyAdmin, click the database you're using for mediawiki along the left side
 * 3) On the next screen, click the "Import" tab at the top.
 * 4) At "Location of the text file", choose one of the files, select compression "None", and click the bottom "Go" button.
 * If your phpMyAdmin screen has only a text field and no text file chooser, click the "SQL" button in the left-side column, under the phpMyAdmin logo, and click the "import files" tab in the new window that opens.
 * 1) Repeat for the second file

On a new wiki
Follow step 1 as above, then run the MediaWiki installation. The MediaWiki installer automatically will do installation tasks if you select the checkbox for CheckUser when prompted for which extensions to install.

Configuration
This tool migrates recent changes data to a separate table, and adds to that when new entries are added. If $wgPutIPinRC was previously set to false, there will be no initial data to search but new edits will fill in as soon as the extension is set up.

After you run the queries, you can reduce $wgRCMaxAge to make recentchanges shorter, without affecting checkuser. Use  to set how far back checkuser data can go, in seconds.

In versions for MediaWiki 1.22 and later, the CheckUser-specific setting $wgCheckUserCIDRLimit determines the largest range that can be checked in a single check. Its format is the same as $wgBlockCIDRLimit. Otherwise, the default limit (for all versions) is /48 for IPv6 checks and /16 for IPv4 checks.

CheckUsers using Mozilla Firefox can add this JS script to their .js file. It makes retrieving IP WHOIS data easier. It requires  support (about:config) enabled. (This can be  in Firefox 3)

Granting right to use CheckUser
To grant the right to use the Check User function, a user with user rights management must go to Special:UserRights and enter the user's name in the box, then select the option "Check User." Once this is done, the Check User option will show up on the Special pages page for that user.

To turn on user rights management for sysops, put the following into LocalSettings.php: To only allow the adding and removing of the checkuser permission, use the following instead:

Basic interface

 * 1) Go to Special:CheckUser.
 * 2) In the user field, type in the username (without the 'user:' prefix), IP address, or CIDR range.
 * 3) * IP: any IPv4 or IPv6 address.
 * 4) * CIDR: you can check a range of IP addresses by appending the CIDR prefix (by default, up to /16 for IPv4 (65,536 addresses), up to /64 for IPv6 (~1.8446*1019 addresses) before revision 7352, up to /48 for IPv6 (~1.2089*1024 addresses or 65536 /64s - controlled by $wgCheckUserCIDRLimit in the latest version) after revision 7352). For notation, see Range blocks.
 * 5) * XFF: you can check a client IP address provided by X-Forwarded-For headers by appending /xff (for example, 127.0.0.1/xff).
 * 6) Select the information you want to retrieve.
 * 7) * Get IPs: returns IP addresses used by a registered user.
 * 8) * Get edits from IP: returns all edits made by a user (registered or anonymous) from an IP address or range.
 * 9) * Get users: returns user accounts that have edited from an IP or range.
 * 10) In the reason field, type in the reason you are accessing the confidential data. Try to succinctly summarise the situation (for example, "cross-wiki spam"); this will be logged in a log visible only to users with the checkuser-log permission.

Information returned
A typical entry in the CheckUser results for a user summary ("get users") is as follows:
 * Example (Talk | contribs) (20:11, -- 20:12, ) [5]
 * 127.0.0.37 XFF: 127.0.0.1, 127.0.0.5

This is formatted to fit a lot of information into a format that can very easily be listed and skimmed, but is difficult to read unless you know what the information provided is. The information is laid out as follows:
 * username (user links) (time period when they edited from the given IP or range) [number of edits from the IP or range]
 * IP address edited from XFF: XFF information provided (can be spoofed)

Each IP/XFF combination used to edit is listed, in order of use.

The last ten user agents (browser, operating system, system language, and versions) for each user for edits made in the IP or range are listed afterwards.

XFF Format
XFF (X-Forwarded-For) headers indicate the series of IP addresses used from the user's computer (first) to the last proxy server. In case of Wikimedia, the last proxy server is one of the Wikimedia proxies (listed under $wgSquidServersNoPurge in the Wikimedia configuration file).

In this example: aaa.aaa.aaa.aaa       XFF: 10.4.46.42, 127.0.0.1, aaa.aaa.aaa.aaa, 208.80.152.46
 * the first two addresses (10.4.46.42, 127.0.0.1) are private to the originating network and can't be reached directly from the public Internet,
 * the third address (aaa.aaa.aaa.aaa) is the "public face" of the editor, usually a broadband or dialup ISP, a company gateway, (but possibly an anonymizer or a malware-compromised server),
 * the last address (208.80.152.46) is one of the Wikimedia squids (sq36.wikimedia.org).

MediaWiki configuration settings $wgUsePrivateIPs, $wgSquidServers, $wgSquidServersNoPurge and extensions using the IsTrustedProxy hook (such as Extension:TrustedXFF) change the way an actual IP address used to attribute edits is selected.

Error messages

 * database query syntax error

If you receive an error message like this when you try to save a page:

A database query syntax error has occurred. This may indicate a bug in the software. The last attempted database query was:

(SQL query hidden)

from within function "efUpdateCheckUserData". Database returned error "1146: Table 'cu_changes' doesn't exist (localhost)".

This means that CheckUser has not been installed correctly. In this case you forgot to create the necessary  table in your database.

API
CheckUser also provides an API.

api.php?action=query&list=checkuser&curequest=userips&cutarget=Jimbo_Wales api.php?action=query&list=checkuser&curequest=edits&cutarget=127.0.0.1/16&xff=1&cureason=Some_check

api.php?action=query&list=checkuserlog&culuser=WikiSysop&cullimit=25 api.php?action=query&list=checkuserlog&cultarget=127.0.0.1&culfrom=20111015230000