Remember when people used to upload their SSH keys onto Github and similar code sharing sites by mistake?
Two years ago, we wrote about the fact that incautious software developers had uploaded hundreds of thousands of private access control keys, entirely unintentionally, along with source code files that they did intend to make public.
Typically, this sort of blunder happens because Linux and Unix computers don’t display directories or filenames that start with a dot character (period, full stop, ASCII 46, hexadecimal 0x2E) by default.
It’s easy to forget that these “hidden” files and directories exist at all, given that you rarely notice they’re there.
One of the super-important “hidden” directories for Unix users is .ssh, which is usually invisible.
So a plain directory listing might look like this:
$ ls -lR .: total 4 drwxr-xr-x 2 lua lua 4096 2021-11-18 20:52 lua-utils/ ./lua-utils: total 32 -rw-r--r-- 1 lua lua 5107 2021-11-18 20:45 args.lua -rw-r--r-- 1 lua lua 12384 2021-11-18 20:45 base.lua -rw-r--r-- 1 lua lua 4628 2021-11-18 20:45 socks5.lua
Blindly packaging all these files into an archive for uploading to your favourite public repository seems pretty harmless, given that all the files in the lua account are supposed to be public.
But if you insist that the file listing utility shows you all files (add the option -a for all to the ls command), including hidden files starting with a dot, you might have a directory tree that looks like this instead:
$ ls -alR .: total 28 drwxr-xr-x 4 lua lua 4096 2021-11-18 20:46 ./ drwxr-xr-x 27 lua lua 16384 2021-11-18 20:42 ../ drwxr-xr-x 2 lua lua 4096 2021-11-18 20:44 .ssh/ drwxr-xr-x 2 lua lua 4096 2021-11-18 20:52 lua-utils/ ./.ssh: total 16 drwxr-xr-x 2 lua lua 4096 2021-11-18 20:44 ./ drwxr-xr-x 4 lua lua 4096 2021-11-18 20:46 ../ -r-------- 1 lua lua 74 2021-11-18 20:45 id_rsa -rw------- 1 lua lua 1993 2021-11-18 20:45 known_hosts ./lua-utils: total 40 drwxr-xr-x 2 lua lua 4096 2021-11-18 20:52 ./ drwxr-xr-x 4 lua lua 4096 2021-11-18 20:46 ../ -rw-r--r-- 1 lua lua 5107 2021-11-18 20:45 args.lua -rw-r--r-- 1 lua lua 12384 2021-11-18 20:45 base.lua -rw-r--r-- 1 lua lua 4628 2021-11-18 20:45 socks5.lua
As you can see, the full directory tree includes a hidden .ssh directory that includes a file called id_rsa, which is a private key file typically containing the login credentials for one or more online servers that you connect to regularly:
$ cat .ssh/id_rsa -----BEGIN RSA PRIVATE KEY----- [. . . .] -----END RSA PRIVATE KEY-----
Did I include 6 files, or only 5?
Of course, if your packaging tool archives and upload all files, not merely the “unhidden” ones, you would inadvertently have included your own private SSH login keys along with your public source code.
Ironically, the id_rsa file might even contain your access key for the very source code repository in which the keyfile is now publicly and searchably sitting.
Faced with this dilemma, many upload sites now go out of their way to find, warn and remove files of this sort, which simply shouldn’t be made public.
But a typical Unix or Linux computer will have hundreds or thousands of hidden files in any busy user’s directory tree, and while only a few of these are as critical as your SSH keys, there many be hundreds, or even thousands, of hidden files that reveal vital secret information about you, your accounts, or your online activities.
Uploading any one of these files by mistake could be harmful to your cyberhealth.
Searches, commands, documents and browsing data
Dozens of popular utilities, for example, retain hidden “history” files that record the last N searches, or the last M documents, or the last P commands you ran, just in case you want to go back quickly to a recent command or document later on.
Often, these history files go back days, week, or even longer – and your command shell history in particular is apt to unwanted copies of your password, “remembered” accidentally when you got out of synch with the password prompt and put in your password at the command prompt by mistake.
Well, reporters over at UK IT news site El Reg, officially The Register, today wrote up a warning that they received from a reader who had just noticed that thousands of copies of Firefox browser cookie files, called cookies.sqlite, could be found on GitHub.
Many Firefox users will never have seen this file, especially on Linux computers, because it’s stashed by default under a directory called .mozilla/firefox, where it’s unlikely to show up during routine browsing of your local files, thanks to the dot at the start of the application-specific directory name .mozilla.
We repeated the experiment, and we immediately found more than 4400 instances of files with that name, with the most recent being just a few hours old.
We didn’t dig too deeply into the files that showed up, even though they’re now a matter of public record, because we suspect that none of the users who had uploaded them intended to do so.
But we were able to open up and scroll briefly through the samples we looked at (.sqlite files are self-contained databases for the popular SQLite toolkit, widely used by a range of applications – it’s very popular on iOS and Android for its compact code size), and they had clear evidence of recent browsing behaviour and site logins.
Of course, cookies.sqlite is just one sensitive file from one popular application, but it’s a bad choice of a private file to upload, because it typically contains personalised informtation about your private browsing habits.
Most importantly, your cookie database may include authentication tokens that let you back into your favourite websites without logging in again next time you visit.
If you are in the habit of telling websites to “remember me for X days” so you don’t need to put in your username, password and 2FA code every morning, it’s a fair guess that the secret string of jumbled text characters that lets you back in next time is stored as a web cookie. Therefore crook who finds your cookie file may be able to copy your personal “login bypass” code and masquerade as you inside your account.
What to do?
- When you’re uploading files for public use, make absolutely certain which files you’ve included in your bundle. Windows famously suppresses file extensions by default, making it hard to be sure which types of file you’ve selected. As shown above, Linux and Unix famously suppress “hidden” files that start with a dot.
- Where possible, get someone else to review your upload before you click [OK]. If you’re uploading your own code, for example, you’re probably feeling relieved and euphoric that your next release is out, or happy that the bugs you’ve been working on are now finally fixed. Reviewing your own uploads is like proofreading your own articles: you know what they are supposed to look like, so mistakes that stick out obviously to other people will often evade your notice entirely.
- Get in the habit of clearing your browser cookies regularly. The longer you leave it, the more personalised data about your browsing your cookie file will contain. Ideally, set up your browser to clear cookies and web data automatically on exit. That way you don’t have to remember to keep doing it by hand. It’s a small inconvenience for big peace of mind.
- Log out from sites as soon as you’ve finished using them. Yes, this is inconvenient, because you have to log back in, and enter your 2FA code, frequently. But when you formally tell a site like GitHub, or YouTube, or Facebook, that you’ve logged out, your current browser authentication tokens are automatically invalidated and therefore become useless to anyone who stumbles across them later on.
- Download your own uploads as soon as they’re public. If you regularly upload files to public repositories where others can fetch them, make a habit of downloading your own uploads (use a different browser, a different username or even a different computer if you can), as if you were an inquisitive member of the public. Review the contents of what you just downloaded, using a tool that you know shows you everything in the download, whatever its extension or filename. If you don’t check for rogue files, crooks are liekly to do it for for you.
Be aware before you share!