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MEDIUM severity

CVE-2021-21284 — moby

MEDIUMFix: moby/moby@64bd448

CVE-2021-21284 is a medium-severity (CVSS 6.8) Path Traversal vulnerability in github.com/moby/moby. A fix is available for github.com/moby/moby — see the affected versions and patch details below.

moby Access to remapped root allows privilege escalation to real root

Also known asGHSA-7452-xqpj-6rpc
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Nov 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.1%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs65th percentile — riskier than 65% of all scored CVEsHighest risk
0.00%0.53%1.05%1.58%0.0%1.1%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected
🐹github.com/moby/moby🐹github.com/moby/moby

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Impact

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.

Patches

Versions 20.10.3 and 19.03.15 contain patches that prevent privilege escalation from remapped user.

Credits

Maintainers would like to thank Alex Chapman for discovering the vulnerability; @awprice, @nathanburrell, @raulgomis, @chris-walz, @erin-jensby, @bassmatt, @mark-adams, @dbaxa for working on it and Zac Ellis for responsibly disclosing it to [email protected]

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/moby/mobyall versions19.3.15go get github.com/moby/moby@v19.3.15
🐹Gogithub.com/moby/moby≥ 20.10.0-beta1&&< 20.10.320.10.3go get github.com/moby/moby@v20.10.3

Affected Products

3 products · 4 configurations
OS
debian linuxdebian
1 version
10.0
Application
dockerdocker
≥ 20.0.0 && < 20.10.3
range
Application
e-series santricity os controllernetapp
≥ 11.0.0 && ≤ 11.60.3
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/moby/moby, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update github.com/moby/moby to 19.3.15 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21284 is resolved across your whole dependency graph.

  3. Workarounds

    Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Frequently Asked Questions

### Impact 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. ### Patches Versions 20.10.3 and 19.03.15 contain patches that prevent privilege escalation from remapped user. ### Credits Maintainers would like to thank Alex Chapman for discovering the vulnerability; @awprice, @nathanburrell, @raulgomis, @chris-walz, @erin-jensby, @bassmatt, @mark-adams, @dbaxa for working on it and Zac Ellis for responsibly disclosing it to secu
O3 Security · Impact-Aware SCA

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CVE-2021-21284: moby PrivEsc — Fixed in 19.3.15