CVE-2019-19921: Race Condition
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.
Specific Go Package Affected github.com/opencontainers/runc/libcontainer
Patches 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.
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 dev@opencontainers.org, or security@opencontainers.org if you think you've found a security bug.
Other sources
A flaw was found in runc. An attacker who controls the container image for two containers that share a volume can race volume mounts during container initialization, by adding a symlink to the rootfs that points to a directory on the volume. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
An attacker who controls the container image for two containers that share a volume can race volume mounts during container initialization, by adding a symlink to the rootfs that points to a directory on the volume.
Upstream Issue:
https://github.com/opencontainers/runc/issues/2197
— Red Hat
runc through 1.0.0-rc9 has Incorrect Access Control leading to Escalation of Privileges, related to libcontainer/rootfslinux.go. To exploit this, an attacker must be able to spawn two containers with custom volume-mount configurations, and be able to run custom images. (This vulnerability does not affect Docker due to an implementation detail that happens to block the attack.)
Affected Software
Remediation
Patch Available
Event History
Parent advisories
This vulnerability appears in the following advisories.
Frequently Asked Questions
What is CVE-2019-19921?
CVE-2019-19921 is a vulnerability found in runc, where an attacker who controls the container image for two containers that share a volume can trick runc into not correctly configuring the container's security labels.
What is the impact of CVE-2019-19921?
The impact of CVE-2019-19921 is that an attacker in control of both containers can exploit the vulnerability to bypass security measures and potentially gain unauthorized access or manipulate container processes.
What is the severity of CVE-2019-19921?
CVE-2019-19921 has a severity level of high.
How can I fix CVE-2019-19921?
To fix CVE-2019-19921, it is recommended to update runc to version 1.0.0-66.rc8.el7_7 or the appropriate patched version provided by your OS or distribution.
Where can I find more information about CVE-2019-19921?
You can find more information about CVE-2019-19921 on CVE.org, NVD, Bugzilla Red Hat, and the Red Hat Errata page.