CVE-2021-20319 — Vulnerability in coreos-installer — CVE Details

### Impact coreos-installer fails to correctly verify GPG signatures when decompressing gzip-compressed artifacts. This allows bypass of signature verification in cases where coreos-installer decompresses a downloaded OS image, allowing an attacker who can modify the OS image to compromise a newly-installed system. Default installations from ISO or PXE media in Fedora CoreOS, RHEL CoreOS, and RHEL for Edge are **not** affected, as coreos-installer installs from an OS image shipped as part of the install media. These flows are affected: 1. Installing with `--image-file`, `--image-url`, or `coreos.inst.image_url`. For example, if a user has a local mirror of installation images, an attacker could replace an image with a gzip-compressed alternative (even if the file extension is `.xz`). The result: ``` $ coreos-installer install --image-url http://localhost:8080/image.xz /dev/loop0 Downloading image from http://localhost:8080/image.xz Downloading signature from http://localhost:8080/image.xz.sig > Read disk 749.9 MiB/749.9 MiB (100%) gpg: Signature made Mon 20 Sep 2021 02:41:50 PM EDT gpg: using RSA key 8C5BA6990BDB26E19F2A1A801161AE6945719A39 gpg: BAD signature from "Fedora (34) <fedora-34-primary@fedoraproject.org>" [ultimate] Install complete. ``` Notice that GPG reports a bad signature, but coreos-installer continues anyway. Automation that relies on coreos-installer's exit status will not notice either. 2. `coreos-installer download --decompress --image-url`: ``` $ coreos-installer download --decompress --image-url http://localhost:8080/image.xz > Read disk 749.9 MiB/749.9 MiB (100%) gpg: Signature made Mon 20 Sep 2021 02:41:50 PM EDT gpg: using RSA key 8C5BA6990BDB26E19F2A1A801161AE6945719A39 gpg: BAD signature from "Fedora (34) <fedora-34-primary@fedoraproject.org>" [ultimate] ./image ``` Again, coreos-installer reports success. 3. Installing with default parameters, when **not** installing from the image built into live ISO or PXE media, if the hosting service is compromised or if an active attacker gains control of the HTTPS response. 4. `coreos-installer download --decompress` if the hosting service is compromised or if an active attacker gains control of the HTTPS response. ### Patches The vulnerability is [fixed](https://github.com/coreos/coreos-installer/pull/659) in coreos-installer 0.10.1. ### Workarounds For `coreos-installer download`, do not use the `-d` or `--decompress` options. For `coreos-installer install`, manually inspect the stderr output. If `BAD signature` appears, do not boot from the target disk. Note, however, that some OS services may have already accessed data on the compromised disk. ### References For more information, see [PR 655](https://github.com/coreos/coreos-installer/pull/655). ### For more information If you have any questions or comments about this advisory, [open an issue in coreos-installer](https://github.com/coreos/coreos-installer/issues/new/choose) or email the CoreOS [development mailing list](https://lists.fedoraproject.org/archives/list/coreos@lists.fedoraproject.org/).