moby Access to remapped root allows privilege escalation to real root
When using --userns-remap, if the root user in the remapped namespace has access to the host filesystem they can modify files under /var/lib/docker/<remapping> that cause writing files with extended privileges.
Versions 20.10.3 and 19.03.15 contain patches that prevent privilege escalation from remapped user.
Maintainers would like to thank Alex Chapman for discovering the vulnerability; @awprice, @nathanburrell, @raulgomis, @chris-walz, @erin-jensby, @bassmatt, @mark-adams, @dbaxa for working on it and Zac Ellis for responsibly disclosing it to security@docker.com
