Vulnerability in docker.io (DEBIAN-CVE-2021-21284)

Summary

Vulnerability in docker.io (DEBIAN-CVE-2021-21284). Data can be tampered with by attackers. Mitigation: upgrade to 20.10.3+dfsg1-1 or later.

Original description

The description as published by the source.

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/" that cause writing files with extended privileges. Versions 20.10.3 and 19.03.15 contain patches that prevent privilege escalation from remapped user.

Source: OSV.dev (Open Source Vulnerabilities) OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as DEBIAN-CVE-2021-21284 has been found in docker.io.
Data can be tampered with by attackers.
What to do: upgrade docker.io to 20.10.3+dfsg1-1 or later.
If unsure, ask your IT team or search "docker.io DEBIAN-CVE-2021-21284" on the vendor's site.

DEBIAN-CVE-2021-21284 (docker.io)
Attack vector: adjacent-network / no user interaction
Patched: 20.10.3+dfsg1-1 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (unclassified) exists in docker.io.

📍 Affected scope

Check the vendor advisory for the affected versions of docker.io.

🔥 Severity

Severity: ?. Data can be tampered with by attackers.

🔧 How to fix

Update to 20.10.3+dfsg1-1.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'docker.io' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

1
Identify exposure identify
```
grep -r 'docker.io' . | grep -v node_modules
```
リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で docker.io を grep し、稼働しているサービス・バージョンを把握する。
2
Apply patch patch
```
Upgrade docker.io to 20.10.3+dfsg1-1
```
ステージング環境で 20.10.3+dfsg1-1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
3
Post-deployment verification verify
```
Confirm patched version is live in production
```
パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

Debian:12 docker.io

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"20.10.3+dfsg1-1"}]}]

Debian:13 docker.io

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"20.10.3+dfsg1-1"}]}]

Debian:14 docker.io

[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"20.10.3+dfsg1-1"}]}]

References

advisory security-tracker.debian.org