Maintain a whitelist of IP address blocks to access AWS over SSH
A small tool to make it pretty simple to add and remove ip addresses (or CIDR blocks) from an AWS security group. This acts like a sort of oversimplified VPN, where you can quickly give yourself SSH access to a project as you move about from network to network.
Anyone who knows enough to use a tool like this likely knows that there are better options available, from hardware VPNs to software VPNs hosted on an EC2 instance, and so forth. If you are using this tool and you haven’t even considered using something better, this is your chance: look at the better options, and see if they fit your needs.
Of course, most of those other options require you to get additional hardware or software resources involved and might come with costs. I understand, that’s why I made a little tool to make do.
This is a python tool, packaged as a python module, so you should be able to just run
$ pip install awswl
Of course, if you don’t know what a python module is, or you don’t have python and pip installed, you may have additional work ahead of you.
The awswl module should be compatible with both python2 and python3; I have Travis building it for Python 2.7, 3.4, 3.5, and 3.6.
If you want usage help at the command line, try:
$ awswl --help
You can list the IP address blocks that are authorized, including which ip address is current:
$ awswl --list
Authorize your current IP Address:
$ awswl --add-current
Remove authorization for your current IP:
$ awswl --remove-current
Authorize a manually-specified CIDR block:
$ awswl --add 192.168.0.0/24
Remove authorization for a manually-specified CIDR block:
$ awswl --remove 192.168.0.0/24
For each of these commands, you need to tell awswl which security group to use, which you can do with the --sgid command-line option or using an environment variable.
In order to get your current ip address, --list, --add-current and --remove-current will make a request to api.ipify.org. I may add a switch to disable that for the privacy- inclined, but feel free to vote for it.
All of these require you to have AWS credentials set up in advance, stored in ~/.aws/credentials, and if you need to use a profile, you can configure it with AWS_PROFILE. If you want to identify the security group using a command-line variable so that you don’t have to put it into each command invocation, you can put it in AWSWL_SGID.
For simple use cases, awswl does everything I want it to do, but it’s currently a pretty thin wrapper over the AWS API for authorizing and revoking access via security groups, and as a result it doesn’t do much pre-processing or validating of your requests. There are cases that it doesn’t address. What it’s good at is adding and removing simple rules containing a simple CIDR block and a single port from a security group.
For instance if you remove a block that isn’t present, AWS may simply ignore the request, because the result matches the desired state – the block isn’t authorized. AWSWL doesn’t check in advance that the block is present, so it doesn’t add any messaging to explain that the block wasn’t removed because it wasn’t present. This is mostly fine, unless you accidentally mistyped, and you failed to remove a block as a result.
Similarly, if what you’ve asked for requires a complex modification of a rule, AWSWL won’t compare your request against the authorized rules and make a plan of action that achieves the desired result. So if there’s already a permission that authorizes a set of CIDR blocks, and you ask to remove one of those CIDR blocks, AWSWL will pass your request on to AWS, which will check to see if there’s a single permission matching your request to revoke, not find it, and not throw an error, and AWSWL will respond that your action succeeded when in fact, nothing changed, and the CIDR block you specified may still be authorized.
Similarly, if you ask AWSWL to revoke permissions on a CIDR block that is narrower than the authorization, you aren’t likely to get the desired result. For instance, if you authorize 192.168.0.0/16 and then revoke 192.168.0.0/24 you could argue that the result should be 192.168.1.0/24 all the way through 192.168.255.0/24 authorized and 192.168.0.0/24 not authorized, but that’s definitely not what will happen.
Similarly it can’t modify a permission block that includes a bunch of ports, including SSH.
To be honest, I am not sure it makes a lot of sense to address those issues so that it can modify rules like that, but I would prefer it to notice when situations like that are present and warn about the rules that it didn’t modify – essentially, I’d like it to validate a bit better.
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