Danny Guo | 郭亚东

I Published My AWS Secret Key to GitHub

August 15, 2018  ·  864 words  ·  ~5 minutes to read

One of my earliest programming projects was a basic news headlines aggregator that would display the top three headlines for each news source. I called it The Daily Lore. The original site was hosted on AWS S3 as a static website. At the time, I didn’t know how to make a dynamic, server-generated website, so my hacky solution for updating the headlines was to run a Python script that would generate a JavaScript file with the headlines hardcoded inside. The script then updated the JS file in the S3 bucket. To automate the updates, I ran the script on a micro EC2 instance in a cron job. Crucially, that means the script needed an AWS secret key.

Eventually, AWS terminated my instance for some reason, and I abandoned the website for a while. I revived it a few years later with a new repo. Last month, I was cleaning up my Google Drive when I came across the old source code. I had stored the .git folder as well, so I decided to push the repo up to GitHub just for fun.

A few minutes later, I got an email:

Amazon Web Services has opened case ******** on your behalf.

The details of the case are as follows:

Case ID: ********

Subject: Your AWS account ******** is compromised

Severity: Urgent

Correspondence: Dear AWS Customer,

Your AWS Account is compromised! Please review the following notice and take immediate action to secure your account.

Your security is important to us. We have become aware that the AWS Access Key ******** along with the corresponding Secret Key is publicly available online at ********.

This poses a security risk to your account and other users, could lead to excessive charges from unauthorized activity or abuse, and violates the AWS Customer Agreement.

Please delete the exposed credentials from your AWS account by using the instructions below and take steps to prevent any new credentials from being published in this manner again. Unfortunately, deleting the keys from the public website and/or disabling them is NOT sufficient to secure your account.

To additionally protect your account from excessive charges, we have temporarily limited your ability to create some AWS resources. Please note that this does not make your account secure, it just partially limits the unauthorized usage for which you could be charged.

Detailed instructions are included below for your convenience.

Immediate actions

First, I let out a loud groan. I immediately knew the consequences of what I had done. I’ve read plenty of stories of nefarious people scraping AWS keys and spinning up tons of EC2 instances for purposes like cryptocurrency mining.

I deleted the GitHub repo, but like the email cautions, I knew that wasn’t enough. Once a secret is compromised once, it’s compromised forever. I went into the AWS console and invalidated the key. Luckily, this was on my personal AWS account, and nothing else depended on that key. I got another AWS email a few minutes later confirming that the compromised key had been deleted.

Then I went through each AWS region to make sure nothing suspicious was present, like newly created servers or IAM users.

Cleaning up and republishing

I still wanted to publish the repo, but I also wanted to scrub the secrets. Even though they were no longer usable, I didn’t want anyone to see them in the future and get the impression that committing secrets is okay. It wouldn’t be enough to just remove them in a new commit because they would still be in the Git history. This part was the silver lining because I knew about the BFG (I assume the name is a reference to the weapon in Doom, but I’m not sure) but had never gotten a chance to use it before. It made it very easy to remove the secrets from the entire history.

I did a more thorough inspection and found other things in the repo that shouldn’t have ever been committed. There were .pyc files. There was a PDF explaining how SVGs work. There was an Excel spreadsheet containing passwords for services that I used for the site. At the time, I wasn’t using a password manager. Fortunately, I had changed all the passwords when I did start using a password manager, so I didn’t need to do so again. Lastly, there was even a SSH private key for logging into the EC2 instance, and a script for doing so that contained the host.

I used the BFG to remove all of these files. I double checked to make sure it worked as expected, and then I re-pushed the repo to GitHub.

Retrospective

I should have done a manual inspection of the files before pushing. I also should have used a tool that is designed to find secrets in Git repos. There are several of them:

I should have distrusted my past self. While it’s secondhand nature to me now to use environment variables for secrets, to think about how they can be leaked, and to be aware of which files should and shouldn’t be committed to Git, I forgot that at one point, I didn’t know any of that. Lesson learned.


← MoMath Hackathon 2018: Vortex Pool Using Mailgun for a Free Custom Domain Email Address →

Found an error or typo? Feel free to open a pull request on GitHub.


comments powered by Disqus