CVE-2021-21284

Name	CVE-2021-21284
Description	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.
Source	CVE (at NVD; CERT, LWN, oss-sec, fulldisc, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
References	DSA-4865-1

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
docker.io (PTS)	bullseye	20.10.5+dfsg1-1+deb11u2	fixed
	bullseye (security)	20.10.5+dfsg1-1+deb11u3	fixed
	bookworm	20.10.24+dfsg1-1+deb12u1	fixed
	sid, trixie	26.1.5+dfsg1-4	fixed

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
docker.io	source	buster	18.09.1+dfsg1-7.1+deb10u3		DSA-4865-1
docker.io	source	(unstable)	20.10.3+dfsg1-1

Notes

https://github.com/moby/moby/security/advisories/GHSA-7452-xqpj-6rpc
https://github.com/moby/moby/commit/1342c51d5e809d2994e6f7e490c8d2b3b12c28ae (v19.03)
https://github.com/moby/moby/commit/5eff67a2c294b7e72607e0949ebc0de21710e4d3 (v19.03)
https://github.com/moby/moby/commit/67de83e70bca92ae6a08e28a03b3fc8fcca9f3f1 (v19.03)