Posts for the month of April 2014

Heartbleed for users

There has been a great deal of commotion about The Heartbleed Bug, particularly from the point of view of server operators. Users are being encouraged to change all their passwords, but--oh, wait--not until after the servers get fixed.

How's a poor user to know when that happens?

Well, you can base it on when the site's SSL cert was issued. If it was issued prior to the Heartbleed announcement, the keys have not been changed (but see update) in response to Heartbleed. That could be for a couple of different reasons. One is that the site was not vulnerable because it was never running a vulnerable version of OpenSSL. The other is that the site was vulnerable, and the vulnerability has been patched, but the operators of the site have not replaced their SSL keys yet.

In either of those two cases, changing your password isn't going to do much. If the site was never vulnerable, your account is not affected. If it was vulnerable, an adversary who got the private keys still has them, and changing your password does little for you.

So once a site updates its SSL cert, it then makes sense to change your password.

How do you know when that happens? Well, if you are using Firefox, you can click on the lock icon, click on the 'more information' button, then the Security tab, then the 'View Certificate' button, then look at the 'Issued On' line. Then close out that window and the previous window. ... For each site you want to check.

That got tedious.

import sys
import ssl
import subprocess
import datetime

def check_bleeding(hostname, port):
    """Returns true if you should change your password."""
    cert = ssl.get_server_certificate((hostname, port))
    task = subprocess.Popen(['openssl', 'x509', '-text', '-noout'],
        stdin=subprocess.PIPE, stdout=subprocess.PIPE)
    readable, _ = task.communicate(cert)
    issued = [line for line in readable.splitlines() if 'Not Before' in
    date_string = issued.split(':', 1)[1].strip()
    issue_date = datetime.datetime.strptime(date_string,
        '%b %d %H:%M:%S %Y %Z')
    return issue_date >= datetime.datetime(2014, 4, 8, 0, 0)

def main(argv):
    """Syntax: python <hostname> [portnumber]"""
    hostname = argv[1]
    if len(argv) > 2:
        port = int(argv[2])
        # 993 and 995 matter for email...
        port = 443
    if check_bleeding(hostname, port):
        sys.stdout.write("Change your password\n")
        sys.stdout.write("Don't bother yet\n")
    return 0

if __name__ == '__main__':

This script checks the issue date of the site's SSL certificate to see if it has been issued since the Heartbleed announcement and tells you if it is time to change your password. If something goes wrong in that process, the script will fail with a traceback; I'm not attempting to make this particularly robust. (Nor, for that matter, elegant.)

If you save a list of hostnames to a file, you can run through them like this:

xargs -n 1 python < account_list

So if you have a file with

you will get

Don't bother yet for
Change your password for

While I would not suggest handing this to someone uncomfortable with a commandline, it is useful for those of us who support friends and family to quickly be able to determine what accounts to recommend they worry about and which to deal with later.

UPDATE: There is a flaw in this approach: I was surprised to learn that the cert that a CA provides to a website operator may have the same issue date as the original cert -- which makes it impossible for the user to determine if the cert is in fact new. With that wrinkle, if you are replacing your cert due to heartbleed, push your CA to give you a cert with a new issue date as evidence that you have fixed your security.

Something I mentioned elsewhere, but did not explicitly state here, is that even with a newly dated cert, a user still cannot tell if the private key was changed along with the cert. If the cert has not changed, the private key has not either. If the operator changes the cert, they will have changed the private key at that point if they are going to do so.

This gets us back to issues of trust. A security mechanism must have a way to recover from a security failure; that is widely understood. But Heartbleed is demonstrating that a security mechanism must include externally visible evidence of the recovery, or the recovery is not complete.

UPDATE: For this site, I buy my SSL cert through DreamHost. I had to open a help ticket to get them to remove the existing cert from the domain in their management application before I could get a new cert. (If you already have a valid cert, the site will let you click on buttons to buy a new cert, but it won't actually take any action on it. That is a reasonable choice in order to avoid customers buying duplicate certs -- but it would be nice to be able to do so anyway.) The response to my help ticket took longer than I would have liked, but I can understand they're likely swamped, and probably don't have a lot of automation around this since they would reasonably not foresee needing it. Once they did that, I then had to buy a new cert from them. I was happy to see that the new cert I bought is good for more than a year -- it will expire when the next cert I would have needed to buy would have expired. Which means that while I had to pay for a new cert, in the long run it will not cost me anything extra. And the new cert has an updated issue date so users can see that I have updated it.