CVE-2021-21284
CWE-22Published: February 2, 2021· Updated: Jun 17, 2026
Official 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.
Technical Analysis
CVE-2021-21284 requires adjacent network access, limiting remote exploitation but still posing risk in shared or local network environments.
Exploitation requires low privileges, which limits the exposure to scenarios where an attacker has already gained initial access.
A successful exploit results in full integrity compromise (data manipulation), with a CVSS base score of 6.8.
The vulnerability has a "Changed" scope, meaning successful exploitation can impact components beyond the vulnerable component itself — such as the host operating system or adjacent services.
CVSS v3.1 Vector Breakdown
Affected Vendors & Products
Exploit & PoC Resources
Official Patches & Advisories
All References (16)
Quick Facts
Related CVEs (CWE-22)
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2021-21284 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts