A vulnerability was found in Buildah. Cache mounts do not properly validate that user-specified paths for the cache are within our cache directory, allowing a RUN instruction in a Container file to mount an arbitrary directory from the host (read/write) into the container as long as those files can be accessed by the user running Buildah.

An incorrect handling of the supplementary groups in the Buildah container engine might lead to the sensitive information disclosure or possible data modification if an attacker has direct access to the affected container where supplementary groups are used to set access permissions and is able to execute a binary code in that container.

A bug was found in Moby (Docker Engine) where containers were incorrectly started with non-empty inheritable Linux process capabilities, creating an atypical Linux environment and enabling programs with inheritable file capabilities to elevate those capabilities to the permitted set during execve(2). Normally, when executable programs have specified permitted file capabilities, otherwise unprivileged users and processes can execute those programs and gain the specified file capabilities up to the bounding set. Due to this bug, containers which included executable programs with inheritable file capabilities allowed otherwise unprivileged users and processes to additionally gain these inheritable file capabilities up to the container's bounding set. Containers which use Linux users and groups to perform privilege separation inside the container are most directly impacted.

This bug did not affect the container security sandbox as the inheritable set never contained more capabilities than were included in the container's bounding set.

Patches This bug has been fixed in Moby (Docker Engine) 20.10.14. Users should update to this version as soon as possible. Running containers should be stopped, deleted, and recreated for the inheritable capabilities to be reset.

This fix changes Moby (Docker Engine) behavior such that containers are started with a more typical Linux environment. Refer to capabilities(7) for a description of how capabilities work. Note that permitted file capabilities continue to allow for privileges to be raised up to the container's bounding set and that processes may add capabilities to their own inheritable set up to the container's bounding set per the rules described in the manual page. In all cases the container's bounding set provides an upper bound on the capabilities that can be assumed and provides for the container security sandbox.

Workarounds The entrypoint of a container can be modified to use a utility like capsh(1) to drop inheritable capabilities prior to the primary process starting.

Impact When running processes using "chroot" isolation, the process being run can examine the environment variables of its immediate parent and grandparent processes (CVE-2021-3602). This isolation type is often used when running buildah in unprivileged containers, and it is often used to do so in CI/CD environments. If sensitive information is exposed to the original buildah process through its environment, that information will unintentionally be shared with child processes which it starts as part of handling RUN instructions or during buildah run. The commands that buildah is instructed to run can read that information if they choose to.

Patches Users should upgrade packages, or images which contain packages, to include version 1.21.3 or later.

Workarounds As a workaround, invoking buildah in a container under env -i to have it started with a reinitialized environment should prevent the leakage.

For more information If you have any questions or comments about this advisory: Open an issue in buildah Email us at the buildah general mailing list, or the podman security mailing list if it's sensitive.

A path traversal flaw was found in Buildah in versions before 1.14.5. This flaw allows an attacker to trick a user into building a malicious container image hosted on an HTTP(s) server and then write files to the user's system anywhere that the user has permissions.

The containers/image library used by container tools; Podman, Builah, and Skopeo in Red Hat Enterprise Linux 8, and CRI-O in OpenShift Container Platform does not enforce TLS connections to the container registry authorization service [1]. An attacker could use this vulnerability launch a MiTM attack, and steal login credentials, or bearer tokens.

Upstream issue:

https://github.com/containers/image/issues/654

Upstream patch:

https://github.com/containers/image/pull/669

[1] https://docs.docker.com/registry/spec/auth/token/