============================================= INTERNET SECURITY AUDITORS ALERT 2009-004 - Original release date: December 3rd, 2008 - Last revised: March 10th, 2009 - Discovered by: Juan Galiana Lara - Severity: 6.3/10 (CVSS scored) ============================================= I. VULNERABILITY ------------------------- WordPress MU < 2.7 'Host' HTTP Header Cross Site Scripting (XSS) Vulnerability II. BACKGROUND ------------------------- WordPress MU, or multi-user, allows to run unlimited blogs with a single install of wordpress. It is most famously used for WordPress.com where it serves tens of millions of hits on hundreds of thousands of blogs each day. Also is used in many other sites like Harvard University and Le Monde. III. DESCRIPTION ------------------------- WordPress MU prior to version 2.7 fails to sanitize the Host header correctly in choose_primary_blog function and is therefore prune to XSS attacks. Web Sites running in a name based virtual hosting setup are not affected while they are not the default virtual host. IV. PROOF OF CONCEPT ------------------------- The snippet of vulnerable code: In wp-includes/wpmu-functions.php, concretly in the function choose_primary_blog: 1830 function choose_primary_blog() { 1831 global $current_user; 1832 ?> 1833 1834 1835 1836 1853 1854

	1837 ID ); 1839 if( count( $all_blogs ) > 1 ) { 1840 $primary_blog = get_usermeta($current_user->ID, 'primary_blog'); 1841 ?> 1842 1847 1852

1855 " http://www.example.com/wp-admin/profile.php> tmp.html $ firefox tmp.html The javascript code will be executed in the context of the victim browser, this can be exploited to steal cookies and escalate privileges to administrator. Tested with Wordpress MU 2.6.5, Apache 2.2 and Mozilla Firefox 3.0.6 V. BUSINESS IMPACT ------------------------- The impact is the attacker can gain administrator privileges on the application. VI. SYSTEMS AFFECTED ------------------------- Versions prior to 2.7 are affected VII. SOLUTION ------------------------- Upgrade to version 2.7 of wordpress multi-user. It can be downloaded from http://mu.wordpress.org VIII. REFERENCES ------------------------- http://mu.wordpress.org IX. CREDITS ------------------------- This vulnerability has been discovered by Juan Galiana Lara (jgaliana (at) isecauditors (dot) com). X. REVISION HISTORY ------------------------- December 03, 2008: Initial release March 02, 2009: More details added XI. DISCLOSURE TIMELINE ------------------------- December 03, 2008: Vendor contacted December 03, 2008: MU trunk code fixed January 28, 2008: WordPress MU 2.7 released March 10, 2009: Vulnerability published by Internet Security Auditors (www.isecauditors.com) XII. LEGAL NOTICES ------------------------- The information contained within this advisory is supplied "as-is" with no warranties or guarantees of fitness of use or otherwise. Internet Security Auditors accepts no responsibility for any damage caused by the use or misuse of this information.