Impact
Access controls for the shim’s API socket verified that the connecting process had an effective UID of 0, but did not otherwise restrict access to the abstract Unix domain socket. This would allow malicious containers running in the same network namespace as the shim, with an effective UID of 0 but otherwise reduced privileges, to cause new processes to be run with elevated privileges.
Specific Go Packages Affected github.com/containerd/containerd/cmd
Patches
This vulnerability has been fixed in containerd 1.3.9 and 1.4.3. Users should update to these versions as soon as they are released. It should be noted that containers started with an old version of containerd-shim should be stopped and restarted, as running containers will continue to be vulnerable even after an upgrade.
Workarounds
If you are not providing the ability for untrusted users to start containers in the same network namespace as the shim (typically the "host" network namespace, for example with docker run --net=host or hostNetwork: true in a Kubernetes pod) and run with an effective UID of 0, you are not vulnerable to this issue.
If you are running containers with a vulnerable configuration, you can deny access to all abstract sockets with AppArmor by adding a line similar to deny unix addr=@, to your policy.
It is best practice to run containers with a reduced set of privileges, with a non-zero UID, and with isolated namespaces. The containerd maintainers strongly advise against sharing namespaces with the host. Reducing the set of isolation mechanisms used for a container necessarily increases that container's privilege, regardless of what container runtime is used for running that container.
Credits
The containerd maintainers would like to thank Jeff Dileo of NCC Group for responsibly disclosing this issue in accordance with the containerd security policy and for reviewing the patch.
For more information
If you have any questions or comments about this advisory:
Open an issue Email us at security@containerd.io if you think you’ve found a security bug.
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 security@containerd.io if you think you’ve found a security bug.