Pulpcore: header content guard filter lets attackers read process environment

An expression language injection has been found in the HeaderContentGuard.permit function in publication.py of the content guard in the Pulpcore package. The guard is supposed to check a value in a request header. It saves a jq filter and runs that filter against the header when a client asks for content. The filter is not limited to the header, and jq's env builtin also returns the environment of the content process. A low-privileged network attacker or user who can create a header content guard and attach it to a distribution can save a filter that reads that environment. The content request is allowed or denied according to the filter result. Repeating the request lets that attacker or user recover the environment, including Pulp settings held there, such as the Django secret key or the database password.