Privilege Escalation via --userns-remap in Docker

CVE-2021-21284 · MEDIUM Severity

CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N

In Docker before versions 9.03.15, 20.10.3 there is a vulnerability involving the --userns-remap option in which 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.

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