CVE-2021-29136

Open Container Initiative umoci before 0.4.7 allows attackers to overwrite arbitrary host paths via a crafted image that causes symlink traversal when "umoci unpack" or "umoci raw unpack" is used.

Impact

umoci 0.4.6 and earlier can be tricked into modifying host files by creating a malicious layer that has a symlink with the name "." (or "/"). Because umoci deletes inodes if they change types, this results in the rootfs directory being replaced with an attacker-controlled symlink. Subsequent image layers will then be applied on top of the target of the symlink (which could be any directory on the host filesystem the user running umoci has access to).

While umoci does have defences against symlink-based attacks, they are all implemented by resolving things relative to the rootfs directory -- if the rootfs itself is a symlink, umoci resolves it first.

This vulnerability affects both "umoci unpack" and "umoci raw unpack".

Patches

This issue has been patched in umoci 0.4.7, see the references section for the specific commit which fixed this vulnerability.

Workarounds

Note that if you use umoci as an unprivileged user (using the --rootless flag) then umoci will not be able to overwrite any files that your user doesn't have access to. Other possible mitigations are to run umoci under an LSM profile such as AppArmor or SELinux to restrict the level of access it has outside of container image directories.

References

• oss-security public disclosure
• patch

Credits

Thanks to Robin Peraglie from Cure53 for discovering and reporting this vulnerability.

For more information

If you have any questions or comments about this advisory

• Open an issue in https://github.com/opencontainers/umoci.
• Email us at [email protected].

Umoci modifies Open Container images. Umoci intends to be a complete manipulation tool for OCI images. In particular, it should be seen as a more end-user-focused version of the oci-image-tools provided by the OCI.

Security Fix(es):

Open Container Initiative umoci before 0.4.7 allows attackers to overwrite arbitrary host paths via a crafted image that causes symlink traversal when "umoci unpack" or "umoci raw unpack" is used.(CVE-2021-29136)

Open Container Initiative umoci before 0.4.7 allows attackers to overwrite arbitrary host paths via a crafted image that causes symlink traversal when "umoci unpack" or "umoci raw unpack" is used.

Improper input validation in umoci in github.com/opencontainers/umoci

A dependency used to extract docker/OCI image layers can be tricked into modifying host files by creating a malicious layer that has a symlink with the name "." (or "/"), when running as root. (CVE-2021-29136) Dde to incorrect use of a default URL, singularity action commands (run/shell/exec) specifying a container using a library:// URI will always attempt to retrieve the container from the default remote endpoint (cloud.sylabs.io) rather than the configured remote endpoint. An attacker may be able to push a malicious container to the default remote endpoint with a URI that is identical to the URI used by a victim with a non-default remote endpoint, thus executing the malicious container. Only action commands (run/shell/exec) against library:// URIs are affected. Other commands such as pull / push respect the configured remote endpoint. (CVE-2021-32635) If a Content-Type header changed between two pulls of the same digest, a client may interpret the resulting content differently. (CVE-2021-41190)

This update for umoci fixes the following issues:

• Update to umoci v0.4.6.
• CVE-2021-29136: malicious layer allows overwriting of host files (bsc#1184147)

This update was imported from the SUSE:SLE-15:Update update project.

This update for singularity fixes the following issues:

singularity was updated to version 3.7.3:

• Fix for CVE-2021-29136: A dependency used to extract docker/OCI image layers can be tricked into modifying host files by creating a malicious layer that has a symlink with the name '.' (or '/'), when running as root.

This update for umoci fixes the following issues:

Update to v0.4.7 (bsc#1184147).

• CVE-2021-29136: Fixed overwriting of host files via malicious layer (bsc#1184147).

This update was imported from the SUSE:SLE-15:Update update project.

This update for umoci fixes the following issues:

Update to v0.4.7 (bsc#1184147).

• CVE-2021-29136: Fixed overwriting of host files via malicious layer (bsc#1184147).

These are all security issues fixed in the singularity-3.8.3-1.2 package on the GA media of openSUSE Tumbleweed.

These are all security issues fixed in the umoci-0.4.7-2.3 package on the GA media of openSUSE Tumbleweed.

This update for umoci fixes the following issues:

• Update to umoci v0.4.6.
• CVE-2021-29136: malicious layer allows overwriting of host files (bsc#1184147)

This update for umoci fixes the following issues:

Update to v0.4.7 (bsc#1184147).

• CVE-2021-29136: Fixed overwriting of host files via malicious layer (bsc#1184147).

This update for umoci fixes the following issues:

Update to v0.4.7 (bsc#1184147).

• CVE-2021-29136: Fixed overwriting of host files via malicious layer (bsc#1184147).