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Date: Mon, 30 Nov 2020 19:00:16 +0000
From: "Karp, Samuel" <skarp@...zon.com>
To: "oss-security@...ts.openwall.com" <oss-security@...ts.openwall.com>
Subject: CVE-2020-15257: containerd-shim API exposed to host network
containers
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.
Patches
This vulnerability has been fixed in containerd 1.3.9 [1] and 1.4.3
[2]. 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 [3] and for reviewing the patch.
For further details, see
https://github.com/containerd/containerd/security/advisories/GHSA-36xw-fx78-c5r4
[1] https://github.com/containerd/containerd/releases/tag/v1.3.9
[2] https://github.com/containerd/containerd/releases/tag/v1.4.3
[3] https://github.com/containerd/project/blob/master/SECURITY.md
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