The bug is known as Heartbleed.
Am I vulnerable?
Generally, you're affected if you run some server that you generated an SSL key for at some point. Most end-users are not (directly) affected; at least Firefox and Chrome don't use OpenSSL. SSH is not affected. The distribution of Ubuntu packages isn't affected (it relies on GPG signatures).
You are vulnerable if you run any kind of server that uses OpenSSL versions 1.0–1.0.1f (except of course versions that were patched since the bug was discovered). The affected Ubuntu versions are 11.10 oneiric through 14.04 trusty pre-releases. It's an implementation bug, not a flaw in the protocol, so only programs that use the OpenSSL library are affected. If you have a program linked against the old 0.9.x version of OpenSSL, it isn't affected. Only programs that use the OpenSSL library to implement the SSL protocol are affected; programs that use OpenSSL for other things are not affected.
If you ran a vulnerable server exposed to the Internet, consider it compromised unless your logs show no connection since the announcement on 2014-04-07. (This assumes that the vulnerability wasn't exploited before its announcement.) If your server was only exposed internally, whether you need to change the keys will depend on what other security measures are in place.
What is the impact?
The bug allows any client who can connect to your SSL server to retrieve about 64kB of memory from the server. The client doesn't need to be authenticated in any way. By repeating the attack, the client can dump different parts of the memory in successive attempts.
One of the critical pieces of data that the attacker may be able to retrieve is the server's SSL private key. With this data, the attacker can impersonate your server.
How do I recover on a server?
Take all affected servers offline. As long as they're running, they're potentially leaking critical data.
libssl1.0.0 package, and make sure that all affected servers are restarted.
You can check if affected processes are still running with ``grep 'libssl.(deleted)' /proc//maps`
Generate new keys. This is necessary because the bug might have allowed an attacker to obtain the old private key. Follow the same procedure you used initially.
- If you use certificates signed by a certification authority, submit your new public keys to your CA. When you get the new certificate, install it on your server.
- If you use self-signed certificates, install it on your server.
- Either way, move the old keys and certificates out of the way (but don't delete them, just ensure they aren't getting used any more).
Now that you have new uncompromised keys, you can bring your server back online.
Revoke the old certificates.
Damage assessment: any data that has been in the memory of a process serving SSL connections may potentially have been leaked. This can include user passwords and other confidential data. You need to evaluate what this data may have been.
- If you're running a service that allows password authentication, then the passwords of users who connected since a little before the vulnerability was announced should be considered compromised. (A little before, because the password may have remained unused in memory for a while.) Check your logs and change the passwords of any affected user.
- Also invalidate all session cookies, as they may have been compromised.
- Client certificates are not compromised.
- Any data that was exchanged since a little before the vulnerability may have remained in the memory of the server and so may have been leaked to an attacker.
- If someone has recorded an old SSL connection and retrieved your server's keys, they can now decrypt their transcript. (Unless PFS was ensured — if you don't know, it wasn't.)
How do I recover on a client?
There are only few situations in which client applications are affected. The problem on the server side is that anyone can connect to a server and exploit the bug. In order to exploit a client, three conditions must be met:
- The client program used a buggy version the OpenSSL library to implement the SSL protocol.
- The client connected to a malicious server. (So for example, if you connected to an email provider, this isn't a concern.) This had to happen after the server owner became aware of the vulnerability, so presumably after 2014-04-07.
- The client process had confidential data in memory that wasn't shared with the server. (So if you just ran
wget to download a file, there was no data to leak.)
If you did that between 2014-04-07 evening UTC and upgrading your OpenSSL library, consider any data that was in the client process's memory to be compromised.