Firefox: How to audit & reset the list of trusted servers/CAs

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 7
  • Red Hat Enterprise Linux 8
  • Red Hat Enterprise Linux 9

Issue

  • How can I check or reset the trusted sites/certificates in Mozilla Firefox?

Resolution

System-wide CA database

Intro to Firefox per-user configuration

  • There is a per-user overlay which allows ...

    • explicit import of new CAs
    • site-specific overrides (i.e., trusting a site without importing a CA)
    • explicit trust-modification of system-provided CAs (e.g., effectively deleting a top-level CA)
    • automatic caching of intermediate CAs

  • Firefox provides an interface to view and modify the per-user certificate overlay under:

    • Preferences → Advanced → Certificates → View Certificates

Auditing Firefox per-user configuration from the command-line

  1. Close all instances of Firefox for relevant user
    This is necessary because changes made on the command-line can be reverted when firefox shuts down

  2. Reset/edit per-user overrides file at ~/.mozilla/firefox/*.default/cert_override.txt
    This is where site-specific exceptions are stored

    • Note that by default, this file doesn't exist or is empty
      Therefore, it's fine to simply delete it

      rm ~/.mozilla/firefox/*.default/cert_override.txt

    • Alternatively, inspect it with the following command

      awk '/^[^#]/ {print $1}' ~/.mozilla/firefox/*.default/cert_override.txt

  3. Reset/edit per-user NSS database at ~/.mozilla/firefox/*.default/
    Modifications to system CA certs (e.g., trust changes) are stored here, as are cached [intermediate] CA certs and site-certs (to be used with the overrides file above)

    • Note that by default this database is empty
      It's fine to simply delete it

      rm ~/.mozilla/firefox/*.default/cert8.db

    • Alternatively, inspect it first with the following command

      certutil -L -d ~/.mozilla/firefox/*.default/

    • Note the Trust Attributes column in the output

      1. Most certs will have only two commas in the trust column
        This means the cert is useless without a proper chain of trust up to a trusted CA; the cert only exists in the db because Firefox cached it

      2. Any certs with characters in the trust column warrant inspection
        See the certutil man page (search for -t trustargs) for details on what the flags mean

    • Inspect a specific cert by appending -n "NICKNAME" to the end of the certutil command (make sure to include the full nickname in quotes to protect against shell word-expansion)

      certutil -L -d ~/.mozilla/firefox/*.default/ -n "corp.example.com"
certutil -L -d ~/.mozilla/firefox/*.default/ -n "Fake Untrustable CA"

    • Delete a specific cert by changing -L to -D

      certutil -D -d ~/.mozilla/firefox/*.default/ -n "corp.example.com"
certutil -D -d ~/.mozilla/firefox/*.default/ -n "Fake Untrustable CA"

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