CVE 2009-2816
The implementation of Cross-Origin Resource Sharing (CORS) in WebKit, as used in Apple Safari before 4.0.4 and Google Chrome before 3.0.195.33, includes certain custom HTTP headers in the OPTIONS request during cross-origin operations with preflight, which makes it easier for remote attackers to conduct cross-site request forgery (CSRF) attacks via a crafted web page.
See the 
CVE page on Mitre.org
for more details.
