Question

Let’s say a page is shown to an authenticated user with various deletion links on it. Each link has a nonce. What’s to prevent a hacker from having sniffed that connection and gotten the nonce, and then immediately using it to delete a bunch of data by spoofing the authenticated user and using the nonce?

Answer 1

Nothing. SSL can help a bit by preventing the sniffing. What you are referring to is called Session Sidejacking

http://en.wikipedia.org/wiki/Session_hijacking

I have also desribed here how you can easily sidejack a
Facebook Session:

http://madhur.github.com/blog/2011/06/12/facebooksessionhijacking.html

LinkedIn Session:

http://www.wtfuzz.com/blogs/linkedin-ssl-cookie-vulnerability/