NCSAM/2011–Post 17–SSL does not make your web site secure
I know, it sounds like complete heresy, but there it is – SSL and HTTPS will not make your web site secure.
Even more appropriate (although I queued the title of this topic up almost a month ago) is this recent piece of news: Top FBI Cyber Cop Recommends New Secure Internet, which appears to make much the opposite point, that all our problems could be fixed if we were only to switch to an Internet in which everyone is identified (something tells me the FBI is not necessarily looking for us to use strong encryption).
HTTPS is just one facet of your web site security
There are a number of ways in which an HTTPS-only website, or HTTPS-only portion of a site, can be insecure. Here’s a list of just some of them:
It’s been a long time since web servers provided only static content in their pages. Now it’s the case that pretty much every web site has to serve “applications”, in which inputs provided by the visitor to the site get processed and involved in outputs.
There are any number of ways in which those inputs can produce bad outputs – Cross Site Scripting (XSS), on which I’ve posted before; Cross Site Request Forgery, allowing an attacker to force you to take actions you didn’t intend; SQL injection, where data behind a web site can be extracted and/or modified – these are just the most commonly known.
Applications can also fail to check credentials, fail to apply access controls, and even fail in some old-fashioned ways like buffer overflows leading to remote code execution.
Providing sensitive information in an application’s path, or through parameters passed in a URL, is another common means by which application authors, who think they are protected by using HTTPS, come a significant cropper. URLs – even HTTPS protected URLs – are often read, logged, and processed at both ends of the connection, and sometimes even in the middle!
Egress filtering in enterprises is often carried out by interrupting the HTTPS communication between client and server, using a locally-deployed trusted root certificate. This quite legitimately allows the egress filtering system to process URLs to determine what’s a safe request, and what’s a dangerous one. This can also cause information sent in a URL to be exposed. This is one reason why an application developer should avoid using GET requests to perform and data exchange for user data, or for data that the site feels is sensitive.
Other path vulnerabilities – mostly fixed these days, but still something that attackers and scanning suites alike feel is worth trying – are those where the path can be changed by embedding extra slash or double-dot characters or sequences. Enough “..” entries in a path, and if the server isn’t properly written or managed, an attacker can escape out of the web server’s restrictions, and visit the operating system disk. The official term for this is a “path traversal attack”.
The presence of a padlock – or whatever your web browser shows to indicate an HTTPS, rather than HTTP, connection, indicates a few things:
- Your communication is encrypted (This can be overcome, but it takes so much work at both client and server for most implementations that I think it’s fair to say you will not be in the situation where you see a padlock without the use of encryption.)
- That doesn’t mean to say you will always have the best encryption around, but if you didn’t go and enable weaker encryption than that supplied in a recent and patched browser, you’re fairly well guaranteed to be safe.
- The web site you are connecting to is at least trying to give some indication of security.
- The web site to which you connected has convinced your browser – or you – that it is who it claims to be in the address bar.
- Note that this may not mean that it passes a test of its identity that you really want. You could be in an enterprise with an SSL-interrupting egress filter, as explained above, you could have been convinced fraudulently to accept the site’s certificate, or you could have installed an inappropriate certificate authority’s root certificate.
If you’re the sort of person who clicks through browser warnings, all you’ve managed to confirm is that your communication is encrypted, and the site you’ve connected to is trying to convince you it is secure. Note that this is exactly what a fraudulent site will try to do. The padlock isn’t everything.
Then think about where your secret information goes. If you’re like a lot of users, you’ll be using the same password on every site you connect to, or some variation thereof. Just because the site uses SSL does not mean that you
But at least it’s a start.
If your bank doesn’t use HTTPS when accepting your logon information, it’s a sign that they really aren’t terribly interested in protecting that transaction. Maybe you should ask them why.
Many web sites will use HTTPS on parts of the site, and HTTP on others. Observe what they choose to protect, and what they choose to leave public. Is the publicly-transmitted information truly public? Is it something you want other people in the coffee shop or library to know you’re browsing?