For web developers, exposing your .git folder to the world is a novice mistake. It allows anyone to download your entire source code repository, which often includes database passwords, salts, hashes, and third party API keys or usernames and passwords.
Over the years, for another personal project, I’ve built up a database of 1.5m reasonably respected domains. These are all either authority sites (such as the BBC or Guardian, or government, educational or military domains), or are domains that have inbound links from at least one of those types of sites.
Out of those 1.5m sites, 2,402 have their .git folder exposed and downloadable. That’s 1 in 600 decent respectable sites, or 0.16% of the internet, that is dangerously exposed.
Some of these .git repositories are harmless, but from a random sample many contain dangerous information that provides a direct vector to attack the site. Hundreds listed database passwords, or included API keys for services such as Amazon AWS or Google Cloud. Others included FTP details to their own web server. Many contained database backups in .SQL files, or the contents of hidden folders that are meant to be restricted.
One prominent human rights group exposed every single person who had signed up to a gay rights campaign (including their home address and email addresses) in a CSV file in their Git repository, publicly downloadable from their website. One company that sold digital reports provided its entire database of reports free of charge to anyone who wanted to download their .git folder.
So developers, please, please check that your .git folder is not visible on your website at http://www.yourdomain.com/.git/. If it is, lock it down immediately. Ideally delete the folder and find a better way to deploy your code, or at least make sure access is forbidden using an .htaccess. Then assume that someone has downloaded everything already and work out what they could have seen. What passwords, salts, hashes or API keys do you need to change? What data could they have accessed? What could they have done to alter or impair your service?
And then please spread the word among other developers too – because right now this must be one of the biggest holes in the internet.