How severe is CVE-2021-43816?

CVE-2021-43816 has a CVSS score of 9.1/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-43816?

CVE-2021-43816 affects the following packages: github.com/containerd/containerd (Go). Ecosystems affected: Go.

How do I fix CVE-2021-43816?

Update github.com/containerd/containerd to 1.5.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-43816 is resolved across your whole dependency graph.

How do I detect CVE-2021-43816 in my Go dependencies?

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

How do I mitigate CVE-2021-43816 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2021-43816 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-43816, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-43816?

CVE-2021-43816 has an EPSS (Exploit Prediction Scoring System) score of 1.7%, placing it in the 76th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-43816?

CVE-2021-43816 is classified as CWE-281 (CWE-281). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-43816 published, and has it been updated?

CVE-2021-43816 was published on January 5, 2022 and was last updated on July 8, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

CRITICAL severity

CVE-2021-43816 — containerd

CRITICALFix: containerd/containerd@a731039

CVE-2021-43816 is a critical-severity (CVSS 9.1) CWE-281 vulnerability in github.com/containerd/containerd. 1 public exploit reference exists, so weaponization risk is real. A fix is available for github.com/containerd/containerd — see the affected versions and patch details below.

Unprivileged pod using `hostPath` can side-step active LSM when it is SELinux

Also known asGHSA-mvff-h3cj-wj9cGO-2022-0278

Published

Jan 5, 2022

Updated

Jul 8, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Oct 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
A successful exploit gives an attacker total control of the affected component, not partial access.

Exploitation and automatability from CISA’s SSVC triage for CVE-2021-43816.

EPSS Exploitation Probability

via FIRST.org ↗

1.7%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs76th percentile — riskier than 76% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-43816 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐹github.com/containerd/containerd

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

Containers launched through containerd’s CRI implementation on Linux systems which use the SELinux security module and containerd versions since v1.5.0 can cause arbitrary files and directories on the host to be relabeled to match the container process label through the use of specially-configured bind mounts in a hostPath volume. This relabeling elevates permissions for the container, granting full read/write access over the affected files and directories. Kubernetes and crictl can both be configured to use containerd’s CRI implementation.

If you are not using containerd’s CRI implementation (through one of the mechanisms described above), you are not affected by this issue.

Patches

This bug has been fixed in containerd 1.5.9. Because file labels persist independently of containerd, users should both update to these versions as soon as they are released and validate that all files on their host are correctly labeled.

Workarounds

Ensure that no sensitive files or directories are used as a hostPath volume source location. Policy enforcement mechanisms such a Kubernetes Pod Security Policy AllowedHostPaths may be specified to limit the files and directories that can be bind-mounted to containers.

For more information

If you have any questions or comments about this advisory:

Open an issue in containerd
Email us at [email protected]

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/containerd/containerd`	≥ 1.5.0&&< 1.5.9	1.5.9`go get github.com/containerd/containerd@v1.5.9`

Affected Products

2 products · 13 configurations

fedorafedoraproject

2 versions

3435

Application

containerdlinuxfoundation

≥ 1.5.1 && < 1.5.9

1 version

1.5.0

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

containerd is an open source container runtime. On installations using S…

github.comNVDApr 2022

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/containerd/containerd, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/containerd/containerd to 1.5.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-43816 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Impact Containers launched through containerd’s CRI implementation on Linux systems which use the SELinux security module and containerd versions since v1.5.0 can cause arbitrary files and directories on the host to be relabeled to match the container process label through the use of specially-configured bind mounts in a hostPath volume. This relabeling elevates permissions for the container, granting full read/write access over the affected files and directories. Kubernetes and crictl can both be configured to use containerd’s CRI implementation. If you are not using containerd’s CRI im