- env variables are prone to be dumped in various contexts and might leak secrets to e.g. logs
- env variables might leak, e.g. in context of docker build stages etc. (but then using building a docker image to build both the image and the software is often anyway not a good idea)
- env variables are often easily accessible by other processes
the method you mentioned of ad-hoc injecting a secret as env by some form of security manager for containers avoid many such problems
A process would need to have the same permission (same user) or root to read /proc/$PID/environ no? or what mechanism is there for a process to read another process env vars (not children processes, that was already mentioned)? unless of course, a process dumped them in some world-readable file (like logs as mentioned) or some other silly way
still works if your system is a single application container
otherwise it does not
This is (part of) the reason programs accept secrets like passwords normally only (or strongly recommended) over stdin or similar instead of env variable or cmdline.
Or why it's not rare (or was in the past, probably is today) to have a encrypted cert file and inject the password to it through a side channel.
It's also not rare for programs to dump environment variables in various situations, including to logs. Or e.g. an intrusion detection program might snapshot all programs running + their cmd arguments + their (creation) env and then run analysis on it.
And while you can use e.g. selinux and similar to add a ton of security and prevent such issues, or use systemd to run the program under ad-hoc users with minimal permissions and various isolation it's very often not done.
Since the rule describes runtime configuration, it shouldn't be involved with the build process at all
I remember reading that it is possible to end up in situations where your environments can end up in the layers of the docker image. Also, you can read the secrets of a container with inspect, and apparently linked containers might be able to access other containers's secrets.
I think it was this article: https://snyk.io/blog/keeping-docker-secrets-secure/
It's similar to the reason that you're not supposed to supply passwords on the command-line (/proc/$PID/cmdline exists), but instead either read them from stdin, or do the big dance of
1. creating a file that contains the password, is owned by root, and is 0400;
2. having your daemon start off running as root for just long enough to read the password into process memory;
3. then having your daemon drop privileges before doing any work, so that someone exploiting the daemon won't have the privilege as the "do the work" user to read the file with the password in it.
Just because a secret is injected into the application as an environment variable does not mean it's handled insecurely elsewhere. For example, AWS ECS containers have built-in support for fetching secrets from Secret Manager at startup and passing them as environment variables: https://docs.aws.amazon.com/AmazonECS/latest/developerguide/...
This fetches the secret at the time the container starts up (IIRC), and uses the IAM credentials of the running application to fetch them from Secret Manager (so it must have permission to the secret).
The merit of using environment variables seems to depend entirely on how they are, well, configured. With a mechanism like this I don't see much disadvantage. (The main disadvantage I see is that generic malware that attempts to dump environment variables might capture them, but defending against that threat is largely obfuscation, unless you aren't storing the secret at all permanently in memory.)