NPAPI plugins, such as Adobe Flash, can send non-simple cross-origin requests, bypassing CORS by making a same-origin POST that does a 307 redirect to the target site. This allows for a malicious site to engage in cross-site request forgery (CSRF) attacks. This vulnerability affects Thunderbird <60,Thunderbird<52.9,FirefoxESR<60.1,FirefoxESR<52.9,andFirefox<61.