Placeholder for security work

[natalieparellano]

Description

The CNB project has been working with OSTIF and Quarkslab on a security review (see https://medium.com/buildpacks/announcing-findings-from-security-audit-b4701f4e8b4b and buildpacks/community#247). This is a placeholder issue for security improvements that will be released in the next minor.

Child issues:

• Security review: run build containers with userns=host #2218
• Security review: launch build containers in a separate ephemeral Docker bridge network #2219
• Security review: set security-opt field to no-new-privileges:true #2220
• Security review: use the untrusted flow when buildpacks are added to a trusted builder #2221
• Security review: warn if NOT --pull-policy=always in container #2222
• Security review: validate application names #2223
• Security review: ensure ownership of build and launch caches #2224
• Security review: investigate which container capabilities are truly needed for build #2225
• Security review: bound buildpack execution time #2226

Proposed solution

Describe alternatives you've considered

Additional context

• This feature should be documented somewhere