CVE-2021-21284 | privilege escalation in Moby

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.

Published: 2021-02-02 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-21284 is rated Moderate Risk (49.3/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 1.06%). EPSS rose +1.04% over the last day, indicating growing attacker interest. Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-21284

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.02% 1.06% +1.04%
2 2025-11-21 0.30% 0.02% -0.28%
3 2025-11-18 — 0.30% —

Full EPSS history (9 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-21284

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.8 3.1 MEDIUM
CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N Click to expand
Attack vector (AV:A)
Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 2.3 4.0 [email protected]
6.8 3.1 MEDIUM
CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N Click to expand
Attack vector (AV:A)
Attacker has to be nearby on the network—same office, same link, that vibe—not the whole wide internet.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 2.3 4.0 [email protected]
2.7 2.0 LOW
AV:A/AC:L/Au:S/C:N/I:P/A:N Click to expand
Access vector (AV:A)
Requires access to an adjacent network segment.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:S)
A single authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 5.1 2.9 [email protected]

Weakness enumeration for CVE-2021-21284

GitHub Security Advisory for CVE-2021-21284

GHSA-7452-xqpj-6rpc · Severity: medium · Ecosystem: go — moby Access to remapped root allows privilege escalation to real root

OS Trackers for CVE-2021-21284

vendor priority summary link
alpine medium CVE-2021-21284: 1 source package rows (docker); 17 state rows across 7 repos (3.17-community, 3.18-community, 3.19-community, 3.20-community, 3.21-community, 3.22-community, edge-community); fixed 7, open 10. https://security.alpinelinux.org/vuln/CVE-2021-21284
debian not yet assigned CVE-2021-21284 not yet assigned priority: Debian including 1 source packages (docker.io), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-21284
gentoo normal CVE-2021-21284: 1 GLSA(s) (202107-23), 1 atom(s) (app-emulation/docker); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-21284
redhat medium — https://access.redhat.com/security/cve/CVE-2021-21284
suse low CVE-2021-21284 severity low: SUSE including 325 source package names (2.0.2-4.2.20:runc-1.0.0~rc93-1.14.2, amazon/suse-sles-15-sp1-chost-byos-v20210304-hvm-ssd-x86_64, …), 1360 product×package rows across 333 product lines (Container rancher/elemental-teal-iso/5.4, Container rancher/elemental-teal-rt/5.4, … (333 product lines)): Fixed 1221, Known Affected 125, Known Not Affected 14. https://www.suse.com/security/cve/CVE-2021-21284/
ubuntu medium CVE-2021-21284 medium priority: Ubuntu including 1 source packages (docker.io), 16 status rows across 16 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): not-affected 9, released 4, DNE 1, ignored 1, needed 1. https://ubuntu.com/security/CVE-2021-21284

Affected software / configurations for CVE-2021-21284

Vendor Product Version Raw CPE
docker docker < 19.03.15 cpe:2.3:a:docker:docker:*:*:*:*:*:*:*:*
docker docker >= 20.0.0, < 20.10.3 cpe:2.3:a:docker:docker:*:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
netapp e-series_santricity_os_controller >= 11.0.0, <= 11.60.3 cpe:2.3:a:netapp:e-series_santricity_os_controller:*:*:*:*:*:*:*:*

References for CVE-2021-21284

cvelogic Threat Intelligence