Summary
Unprivileged pod using hostPath can side-step active LSM when it is SELinux
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]
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.
CVE-2021-43816 has a CVSS score of 8.0 (High). The vector is network-reachable, high privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.5.9); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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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.
Frequently Asked Questions
- What is CVE-2021-43816? CVE-2021-43816 is a high-severity security vulnerability in github.com/containerd/containerd (go), affecting versions >= 1.5.0, < 1.5.9. It is fixed in 1.5.9.
- How severe is CVE-2021-43816? CVE-2021-43816 has a CVSS score of 8.0 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of github.com/containerd/containerd are affected by CVE-2021-43816? github.com/containerd/containerd (go) versions >= 1.5.0, < 1.5.9 is affected.
- Is there a fix for CVE-2021-43816? Yes. CVE-2021-43816 is fixed in 1.5.9. Upgrade to this version or later.
- Is CVE-2021-43816 exploitable, and should I be worried? Whether CVE-2021-43816 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-43816 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-43816? Upgrade
github.com/containerd/containerdto 1.5.9 or later.