Is it secure to submit from a HTTP form to HTTPS?

Question

Is it acceptable to submit from an http form through https? It seems like it should be secure, but it allows for a man in the middle attack (here is a good discussion). There are sites like mint.com that allow you to sign-in from an http page but does an https post. In my site, the request is to have an http landing page but be able to login securely. Is it not worth the possible security risk and should I just make all users go to a secure page to login (or make the landing page secure)?

Answer 1

Jay and Kiwi are right about the MITM attack. However, its important to note that the attacker doesn't have to break the form and give some error message; the attacker can instead insert JavaScript to send the form data twice, once to him and once to you.

But, honestly, you have to ask, what's the chance of an attacker intercepting your login page and modifying it in flight? How's it compare to the risk of (a) doing a MITM attack strait on the SSL session, and hoping the user presses "OK" to continue; (b) doing the MITM on your initial redirect to SSL (e.g., from http://example.com to https://example.com) and redirecting to https://doma1n.com instead, which is under the attacker's control; (c) You having a XSS, XSRF, or SQL injection flaw somewhere on your site.

Yes, I'd suggest running the login form under SSL, there isn't any reason not to. But I wouldn't worry much if it weren't, there are probably much lower hanging fruit.

Update

The above answer is from 2008. Since then, a lot of additional threats have become apparent. E.g., access sites from random untrusted networks such as WiFi hotspots (where anyone nearby may be able to pull off that attack). Now I'd say yes, you definitely should encrypt your login page, and further your entire site. Further, there are now solutions to the initial redirect problem (HTTP Strict Transport Security). The Open Web Application Security Project makes several best practices guides available.

Answer 2

Posting a form from an http page to an https page does encrypt the data in the form when it is transmitted in the most simple terms. If there is a man-in-the-middle attack, the browser will warn you.

However, if the original http form was subjected to man-in-the-middle and the https post-back address was modified by the attacker, then you will get no warning. The data will still actually be encrypted, but the man-in-the-middle attacker would be able to decrypt (since he sent you the key in the first place) and read the data.

Also, if the form is sending things back through other means (scripted connections) there may be a possibility of unencrypted data being sent over the wire before the form is posted (although any good website would never do this with any kind of sensitive data).

Answer 3

No, it's not secure to go from HTTP to HTTPS. The originating and resulting points of the request must be HTTPS for the secure channel to be established and utilized.

Answer 4

One of the biggest things missed out in all of the above is that there is a general trend to place a login on a home page (Huge trend in User Experience Trends).

The big problem here is that Google does not like to search secure pages with good reason, so all those Devs who are wondering why not make it all secure, well if you want your page invisible to Google, secure it all. Else, the second best option to post from http to https is the lesser of two evils at this point?

Answer 5

Is there any reason not to use HTTPS for the entire transaction? If you can't find a very good one, use it!

• It's arguably simpler than switching protocols.

• The MITM risk is real.

• Following your link, the user "Helios" makes an excellent point that using 100% HTTPS is far less confusing to the user.

Answer 6

For me (as an end-user), the value of an HTTPS session is not only that the data is encrypted, but that I have verification that the page I'm typing my super-secrets into has come from the place I want it to.

Having the form in a non-HTTPS session defeats that assurance.

(I know - this is just another way of saying that the form is subject to an MITM attack).