NVD / CVE Program· CNA GitHub_M

CVE-2021-21284: privilege escalation in Moby

MediumCVSS 6.8 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 27/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 1% (FIRST EPSS); higher than 65.4% of all records.
Someone on the same network segment can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
Fixed version: docker (Alpine:v3.12) 20.10.3-r0; docker.io (Debian:10) 18.09.1+dfsg1-7.1+deb10u3; docker.io (Debian:12) 20.10.3+dfsg1-1.
Mentioned 3 times in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to docker (Alpine:v3.12) 20.10.3-r0; docker.io (Debian:10) 18.09.1+dfsg1-7.1+deb10u3; docker.io (Debian:12) 20.10.3+dfsg1-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

Path traversal

Published: Feb 2, 2021
Updated: Jun 16, 2026
EPSS: 1.0% · 65th percentile
CWE: CWE-22

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 27 / 40 · 6.8 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 1.0%

CNA vs NVD score

NVD: 6.8
CNA · GitHub_M: 6.8; agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Is your version affected? Check it

Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
docker	docker	cpe:2.3:a:docker:docker
debian	debian linux	cpe:2.3:o:debian:debian_linux
netapp	e-series santricity os controller	cpe:2.3:a:netapp:e-series_santricity_os_controller

Using docker? Add it to your stack and be the first to know about CVEs like this one. (Docker)

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

moby moby
- < 19.03.15, >= 20.0.0, < 20.10.3affected

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

docker dockerbefore 19.03.15
docker docker20.0.0 and later · before 20.10.3

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Alpine:v3.12	docker	from 20.0.0 · before 20.10.3-r0	20.10.3-r0
Debian:10	docker.io	before 18.09.1+dfsg1-7.1+deb10u3	18.09.1+dfsg1-7.1+deb10u3
Debian:12	docker.io	before 20.10.3+dfsg1-1	20.10.3+dfsg1-1
Go	github.com/moby/moby	from 20.10.0-beta1 · before 20.10.3	20.10.3
Go	github.com/moby/moby	before 19.3.15	19.3.15
openSUSE:Leap 15.2	containerd	before 1.4.4-lp152.2.6.1	1.4.4-lp152.2.6.1
openSUSE:Leap 15.2	containerd	before 1.3.9-lp152.2.3.1	1.3.9-lp152.2.3.1
openSUSE:Leap 15.2	docker	before 19.03.15_ce-lp152.2.3.1	19.03.15_ce-lp152.2.3.1
openSUSE:Leap 15.2	docker	before 20.10.6_ce-lp152.2.12.1	20.10.6_ce-lp152.2.12.1
openSUSE:Leap 15.2	docker-runc	before 1.0.0rc10+gitr3981_dc9208a3303f-lp152.2.3.1	1.0.0rc10+gitr3981_dc9208a3303f-lp152.2.3.1
openSUSE:Leap 15.2	fish	before 2.7.1-lp152.5.3.1	2.7.1-lp152.5.3.1
openSUSE:Leap 15.2	golang-github-docker-libnetwork	before 0.7.0.1+gitr2908_55e924b8a842-lp152.2.3.1	0.7.0.1+gitr2908_55e924b8a842-lp152.2.3.1
openSUSE:Leap 15.2	runc	before 1.0.0~rc93-lp152.2.3.1	1.0.0~rc93-lp152.2.3.1
openSUSE:Leap 15.3	containerd	before 1.4.4-5.32.1	1.4.4-5.32.1
openSUSE:Leap 15.3	docker	before 20.10.6_ce-6.49.3	20.10.6_ce-6.49.3
openSUSE:Leap 15.3	runc	before 1.0.0~rc93-1.14.2	1.0.0~rc93-1.14.2
openSUSE:Tumbleweed	docker	before 20.10.6_ce-2.1	20.10.6_ce-2.1
SUSE:Linux Enterprise Module for Containers 12	containerd	before 1.3.9-16.35.1	1.3.9-16.35.1
SUSE:Linux Enterprise Module for Containers 12	containerd	before 1.4.4-16.38.1	1.4.4-16.38.1
SUSE:Linux Enterprise Module for Containers 12	docker	before 19.03.15_ce-98.60.2	19.03.15_ce-98.60.2
SUSE:Linux Enterprise Module for Containers 12	docker	before 20.10.6_ce-98.66.1	20.10.6_ce-98.66.1
SUSE:Linux Enterprise Module for Containers 12	docker-runc	before 1.0.0rc10+gitr3981_dc9208a3303f-1.52.1	1.0.0rc10+gitr3981_dc9208a3303f-1.52.1
SUSE:Linux Enterprise Module for Containers 12	golang-github-docker-libnetwork	before 0.7.0.1+gitr2908_55e924b8a842-37.1	0.7.0.1+gitr2908_55e924b8a842-37.1
SUSE:Linux Enterprise Module for Containers 12	runc	before 1.0.0~rc93-16.8.1	1.0.0~rc93-16.8.1

Same product

docker: all records

Other highest-scoring records for the same primary product.

CVE-2019-15752Docker Desktop Community Edition before 2.1.0.1 allows local users to gain privileges by placing a Trojan horse…KEV
76This week
CVE-2019-5736runc through 1.0-rc6, as used in Docker before 18.09.2 and other products, allows attackers to overwrite the host runc binary (and…
64This week
CVE-2019-14271In Docker 19.03.x before 19.03.1 linked against the GNU C Library (aka glibc), code injection can occur when the nsswitch facility…
45Plan

Published before and after this one in the same product

← EarlierCVE-2020-27534Dec 30, 2020 · util/binfmt_misc/check.go in Builder in Docker Engine before 19.03.9 calls os.OpenFile with a potentially unsafe qemu-check temporary…
22Monitor
← EarlierCVE-2021-3162Jan 15, 2021 · Docker Desktop Community before 2.5.0.0 on macOS mishandles certificate checking, leading to local privilege escalation.
31Monitor
Later →CVE-2021-21285Feb 2, 2021 · Docker daemon crash during image pull of malicious image
27Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
alpine:docker	20.10.3-r0 · Alpine:v3.12	Package registry (OSV)
debian:docker.io	20.10.3+dfsg1-1 · Debian:12	Package registry (OSV)
Go:github.com/moby/moby	19.3.15	Package registry (OSV)
Go:github.com/moby/moby	20.10.3	Package registry (OSV)
opensuse:containerd	1.3.9-lp152.2.3.1 · openSUSE:Leap 15.2	Package registry (OSV)
opensuse:docker	19.03.15_ce-lp152.2.3.1 · openSUSE:Leap 15.2	Package registry (OSV)
opensuse:docker-runc	1.0.0rc10+gitr3981_dc9208a3303f-lp152.2.3.1 · openSUSE:Leap 15.2	Package registry (OSV)
opensuse:fish	2.7.1-lp152.5.3.1 · openSUSE:Leap 15.2	Package registry (OSV)
opensuse:golang-github-docker-libnetwork	0.7.0.1+gitr2908_55e924b8a842-lp152.2.3.1 · openSUSE:Leap 15.2	Package registry (OSV)
opensuse:runc	1.0.0~rc93-lp152.2.3.1 · openSUSE:Leap 15.2	Package registry (OSV)
suse:containerd	1.3.9-5.29.3 · SUSE:Linux Enterprise Module for Containers 15 SP2	Package registry (OSV)
suse:docker	19.03.15_ce-6.43.3 · SUSE:Linux Enterprise Module for Containers 15 SP2	Package registry (OSV)
suse:docker-runc	1.0.0rc10+gitr3981_dc9208a3303f-6.45.3 · SUSE:Linux Enterprise Module for Containers 15 SP2	Package registry (OSV)
suse:golang-github-docker-libnetwork	0.7.0.1+gitr2908_55e924b8a842-4.28.3 · SUSE:Linux Enterprise Module for Containers 15 SP2	Package registry (OSV)
suse:runc	1.0.0~rc93-16.8.1 · SUSE:Linux Enterprise Module for Containers 12	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

moby/mobycommit 64bd448

Bug bounty scope

The product’s vendor appears in a public program. Matched by name; verify the scope text in the program.

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

TR-21-0448 · Jun 7, 2021(IBM Güvenlik Bülteni Yayınladı)
TR-21-0216 · Mar 10, 2021(IBM Güvenlik Bülteni Yayınladı)
TR-21-0097 · Feb 3, 2021(Docker Güvenlik Zafiyeti)

All national notices →

Not on record for this CVE: EPSS history · researcher credit · variant or chain candidate.

Technical details

Attack conditions

Someone on the same network segment can trigger it.
A low-privileged account is enough.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: high · data or configuration can be modified
Availability: none

Impact can extend beyond the vulnerable component (scope changes).

Attack vector: Adjacent
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Changed
Confidentiality impact: None
Integrity impact: High
Availability impact: None

Weakness class (CWE)

CWE-22 · Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

CVSS vector

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

nvd-primary

Root cause

A user-supplied file name is joined with the allowed directory, but the result is never checked to confirm it is still inside that directory.

The bug in code

The whole CWE-22 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1const file = path.join(ROOT, req.query.name);
2res.sendFile(file);

Fixed

1const file = path.resolve(ROOT, req.query.name);
2if (!file.startsWith(ROOT + path.sep)) {
3  return res.sendStatus(400);
4}
5res.sendFile(file);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log (1)

Fix✗ → ✓Sep 28, 2026, 10:45 PM UTC

For records you follow, these changes also arrive as notifications. →

References

docs.docker.com/engine/release-notes/#20103

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records