How severe is CVE-2021-21334?

CVE-2021-21334 has a CVSS score of 6.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-21334?

CVE-2021-21334 affects the following packages: github.com/containerd/containerd (Go), github.com/containerd/containerd (Go). Ecosystems affected: Go.

How do I fix CVE-2021-21334?

Update github.com/containerd/containerd to 1.4.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21334 is resolved across your whole dependency graph.

How do I detect CVE-2021-21334 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-2021-21334 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-2021-21334 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-21334 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-21334?

CVE-2021-21334 has an EPSS (Exploit Prediction Scoring System) score of 2.0%, placing it in the 81th 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-2021-21334?

CVE-2021-21334 is classified as CWE-668 (CWE-668). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-21334 published, and has it been updated?

CVE-2021-21334 was published on March 10, 2021 and was last updated on October 20, 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

MEDIUM severity

CVE-2021-21334 — containerd

MEDIUMFix: containerd/containerd@05f951a

CVE-2021-21334 is a medium-severity (CVSS 6.3) CWE-668 vulnerability in github.com/containerd/containerd. A fix is available for github.com/containerd/containerd — see the affected versions and patch details below.

containerd environment variable leak

Also known asGHSA-6g2q-w5j3-fwh4

Published

Mar 10, 2021

Updated

Oct 20, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

2.0%probability of exploitation in next 30 days

Lower Risk+0.08%

Lower risk than most CVEs81th percentile — riskier than 81% of all scored CVEsHighest risk

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/containerd/containerd🐹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 (through Kubernetes, crictl, or any other pod/container client that uses the containerd CRI service) that share the same image may receive incorrect environment variables, including values that are defined for other containers. If the affected containers have different security contexts, this may allow sensitive information to be unintentionally shared.

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

If you are not launching multiple containers or Kubernetes pods from the same image which have different environment variables, you are not vulnerable to this issue.

If you are not launching multiple containers or Kubernetes pods from the same image in rapid succession, you have reduced likelihood of being vulnerable to this issue

Patches

This vulnerability has been fixed in containerd 1.3.10 and containerd 1.4.4. Users should update to these versions as soon as they are released.

Workarounds

There are no known workarounds.

For more information

If you have any questions or comments about this advisory:

Open an issue
Email us at [email protected] if you think you’ve found a security bug.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/containerd/containerd`	≥ 1.4.0&&< 1.4.4	1.4.4`go get github.com/containerd/containerd@v1.4.4`
🐹Go	`github.com/containerd/containerd`	all versions	1.3.10`go get github.com/containerd/containerd@v1.3.10`

Affected Products

2 products · 4 configurations

fedorafedoraproject

2 versions

3334

Application

containerdlinuxfoundation

≥ 1.4.0 && < 1.4.4

range

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 1.4.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21334 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 (through Kubernetes, crictl, or any other pod/container client that uses the containerd CRI service) that share the same image may receive incorrect environment variables, including values that are defined for other containers. If the affected containers have different security contexts, this may allow sensitive information to be unintentionally shared. If you are not using containerd’s CRI implementation (through one of the mechanisms described above), you are not vulnerable to this issue. If you are not launching multi

O3 Security · Impact-Aware SCA

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