CVE-2026-52763: YesWiki: SQL injection via the `recentchanges` action `period` argument leads to arbitrary DB read

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.