Summary
opencontainers runc contains procfs race condition with a shared volume mount
Specific Go Package Affected
github.com/opencontainers/runc/libcontainer
Workarounds
If you are not providing the ability for untrusted users to configure mountpoints for runc (or through a higher-level tool such as docker run -v) then you are not vulnerable to this issue. This exploit requires fairly complicated levels of access (which are available for some public clouds but are not necessarily available for all deployments).
Additionally, it appears as though it is not possible to exploit this vulnerability through Docker (due to the order of mounts Docker generates). However you should not depend on this, as it may be possible to work around this roadblock.
Credits
This vulnerability was discovered by Cure53, as part of a third-party security audit.
For more information
If you have any questions or comments about this advisory:
- Open an issue.
- Email us at [email protected], or [email protected] if you think you've found a security bug.
Impact
By crafting a malicious root filesystem (with /proc being a symlink to a directory which was inside a volume shared with another running container), an attacker in control of both containers can trick runc into not correctly configuring the container's security labels and not correctly masking paths inside /proc which contain potentially-sensitive information about the host (or even allow for direct attacks against the host).
In order to exploit this bug, an untrusted user must be able to spawn custom containers with custom mount configurations (such that a volume is shared between two containers). It should be noted that we consider this to be a fairly high level of access for an untrusted user -- and we do not recommend allowing completely untrusted users to have such degrees of access without further restrictions.
Multiple concurrent operations access a shared resource without proper synchronization, producing unpredictable results depending on timing. Typical impact: TOCTOU exploits, data corruption, or privilege escalation.
CVE-2019-19921 has a CVSS score of 5.0 (Medium). The vector is network-reachable, no 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 (1.0.0-rc9.0.20200122160610-2fc03cc11c77); 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 vulnerability has been fixed in 1.0.0-rc10. It should be noted that the current fix is effectively a hot-fix, and there are known ways for it to be worked around (such as making the entire root filesystem a shared volume controlled by another container). We recommend that users review their access policies to ensure that untrusted users do not have such high levels of controls over container mount configuration.
Frequently Asked Questions
- What is CVE-2019-19921? CVE-2019-19921 is a medium-severity race condition vulnerability in github.com/opencontainers/runc (go), affecting versions < 1.0.0-rc9.0.20200122160610-2fc03cc11c77. It is fixed in 1.0.0-rc9.0.20200122160610-2fc03cc11c77. Multiple concurrent operations access a shared resource without proper synchronization, producing unpredictable results depending on timing.
- How severe is CVE-2019-19921? CVE-2019-19921 has a CVSS score of 5.0 (Medium). 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/opencontainers/runc are affected by CVE-2019-19921? github.com/opencontainers/runc (go) versions < 1.0.0-rc9.0.20200122160610-2fc03cc11c77 is affected.
- Is there a fix for CVE-2019-19921? Yes. CVE-2019-19921 is fixed in 1.0.0-rc9.0.20200122160610-2fc03cc11c77. Upgrade to this version or later.
- Is CVE-2019-19921 exploitable, and should I be worried? Whether CVE-2019-19921 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-2019-19921 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-2019-19921? Upgrade
github.com/opencontainers/runcto 1.0.0-rc9.0.20200122160610-2fc03cc11c77 or later.