What’s Vulnerable › Vulnerabilities
CVE-2021-21284: privilege escalation in Moby
- Severity: medium (CVSS 6.8 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 1.1% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2021-02-02 · updated 2026-06-17
- Weakness: CWE-22
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.
Affected products
- Debian Linux: 10.0
- Docker Engine: before 19.03.15; from 20.0.0 before 20.10.3 — fixed in 19.03.15, 20.10.3
- E-Series SANtricity OS Controller Software 11.x: from 11.0.0 through 11.60.3
How to fix
Upgrade to a fixed version: Docker Engine 19.03.15, 20.10.3. Check the vendor advisory for mitigations.
References
- https://docs.docker.com/engine/release-notes/#20103
- https://github.com/moby/moby/commit/64bd4485b3a66a597c02c95f5776395e540b2c7c
- https://github.com/moby/moby/releases/tag/v19.03.15
- https://github.com/moby/moby/releases/tag/v20.10.3
- https://github.com/moby/moby/security/advisories/GHSA-7452-xqpj-6rpc
- https://security.gentoo.org/glsa/202107-23
- https://security.netapp.com/advisory/ntap-20210226-0005/
- https://www.debian.org/security/2021/dsa-4865
- https://docs.docker.com/engine/release-notes/#20103
- https://github.com/moby/moby/commit/64bd4485b3a66a597c02c95f5776395e540b2c7c
- https://github.com/moby/moby/releases/tag/v19.03.15
- https://github.com/moby/moby/releases/tag/v20.10.3
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