Saturday, October 24, 2020

Defense in Depth: Read-Only Document Root

One security rule I live by as a sysadmin, which admittedly causes me a lot of trouble with PHP apps, is that the running web server user is never able to write to files within the document root.

Any user-file upload/download mechanism goes somewhere else, so that read access can do a permission check, and be delivered through readfile() or a redirect to a CDN, not passed through a complex mechanism that may decide to execute the file's contents.

Configuration files are similarly locked down.  A project that configures itself with PHP code is a project that offers arbitrary code execution to anyone who can change that configuration file.

I don't let the web user install new code to /bin; we shouldn't let the web user install new code to /srv/www. It's the server, not a system administrator.

Not coincidentally, our document root is never the root of a git repository.  It's typically placed in a public folder, allowing us to have a special writable folder like cache both within the project/deployment, and outside of the document root.

Saturday, October 17, 2020

MySQL on MacOS: Discoveries

For a long time, I’ve installed MySQL within my development virtual machine (VM), loaded it with a minimal subset of production data, and pointed the database hostname to through the VM’s /etc/hosts file.

However, working from home, I realized that the my slower DSL connection did not affect the amount of time it took to pull a fresh subset of production data into the VM.

I finally went to the trouble of installing MySQL on the host side, and configuring everything to work with that, so that filling it does not require the data to cross any hypervisor boundaries at all.  And I learned some things!

  1. The installer sets it up to launch as _mysql user
  2. Using the wrong CA certificate causes padding errors
  3. MySQL 8.0.14+ allows a separate "administrative management" port
  4. MySQL’s AES_ENCRYPT() function makes the worst possible choice by default
  5. The speedup is dominated by MySQL's disk access