Simon Willison’s Weblog

Items tagged security, flash

Filters: security × flash ×


CSRF: Flash + 307 redirect = Game Over. Here’s the exploit that Django and Rails both just released fixes for. It’s actually a flaw in the Flash player. Flash isn’t meant to be able to make cross-domain HTTP requests with custom HTTP headers unless the crossdomain.xml file on the other domain allows them to, but it turns out a 307 redirect (like a 302, but allows POST data to be forwarded) confuses the Flash player in to not checking the crossdomain.xml on the host it is being redirect to. # 10th February 2011, 10:07 pm

Cross-domain policy file usage recommendations for Flash Player. One of the best explanations of the security implications of crossdomain.xml files I’ve seen. If you host a crossdomain.xml file with allow-access-from domain=“*” and don’t understand all of the points described here, you probably have a nasty security vulnerability. # 5th November 2009, 4:24 pm

Facebook and MySpace security: backdoor wide open, millions of accounts exploitable (via) Amazingly, both services had wide open holes in their crossdomain.xml files. Facebook were serving allow-access-from-domain=“*” in the crossdomain.xml file on one of their subdomains (a subdomain that still had access to the user’s profile information) while MySpace were opting in farm.sproutbuilder.com, a service which allowed anyone to upload arbitrary SWF files. # 5th November 2009, 9:47 am

You Deleted Your Cookies? Think Again (via) Flash cookies last longer than browser cookies and are harder to delete. Some services are sneakily “respawning” their cookies—if you clear the regular tracking cookie it will be reinstated from the Flash data next time you visit a page. # 17th August 2009, 3:23 pm

Poking new holes with Flash Crossdomain Policy File. This is an old article from 2006 which describes the crossdomain.xml hidden in a GIF exploit I referred to in an earlier post (scroll down to the appendix for an example). As far as I know the Flash Player’s crossdomain.xml parser has been tightened up since. # 1st July 2008, 4:12 pm

Scaring people with fullScreen. Unsurprisingly, you can work around the “Press Esc to exit full screen mode” message in Flash by distracting the user with lots of similar looking visual noise. This opens up opportunities for cunning phishing attacks that simulate the chrome of the entire operating system. EDIT: Comments point out that text entry via the keyboard is still disabled, limiting the damage somewhat. # 2nd June 2008, 10:18 pm

Crossdomain.xml Invites Cross-site Mayhem. A useful reminder that crossdomain.xml files should be treated with extreme caution. Allowing access from * makes it impossible to protect your site against CSRF attacks, and even allowing from a “circle of trust” of domains can be fatal if just one of those domains has an XSS hole. # 15th May 2008, 8:06 am

XSS Vulnerabilities in Common Shockwave Flash Files. Is the word “shockwave” still relevant to Flash? Regardless, it turns out Flash can be a serious vector for XSS attacks, and many commonly used components have recently fixed holes (and hence should be updated ASAP). # 6th January 2008, 9:35 am