CVE-2026-41567

Moby is an open source container framework. In versions prior to 29.5.1 and in moby/moby v2 prior to v2.0.0-beta.14, when a compressed archive is uploaded to a container via `PUT /containers/{id}/archive` or piped through `docker cp -`, the daemon resolves decompression binaries (such as `xz` or `unpigz`) from the container's filesystem rather than the host's due to incorrect ordering of operations. A malicious container image containing a trojanized decompression binary can achieve arbitrary code execution with full daemon privileges, including host root UID and unrestricted capabilities, when a user uploads a compressed (xz or gzip) archive into that container. This issue is fixed in Docker Engine 29.5.1 and moby/moby v2.0.0-beta.14. Workarounds include only running containers from trusted images, using authorization plugins to restrict access to the `PUT /containers/{id}/archive` endpoint, and avoiding piping compressed archives into containers created from untrusted images

The Docker daemon's implementation of the "PUT /containers/{id}/archive" endpoint executes a container binary on the host when extracting an archive to a container. On Unix-like systems, this can be exploited if an attacker can control the container's filesystem or the archive being extracted, potentially leading to privilege escalation or host compromise. The affected code is located in the daemon package, specifically in the containerExtractToDir method of the Daemon struct. This package is part of the Moby daemon's core and is not intended for external use as a library.

## Summary When a user uploads a compressed archive into a container, a malicious image can execute arbitrary code with daemon (host root) privileges. ## Details When handling `PUT /containers/{id}/archive` requests with compressed archives, the daemon decompresses them using external system binaries. Due to incorrect ordering of operations, these binaries are resolved from the container's filesystem rather than the host's. A container image that includes a trojanized decompression binary can achieve code execution as the daemon process whenever a compressed archive is uploaded to that container. The executed binary runs with the daemon's full privileges, including host root UID and unrestricted capabilities. ## Impact Arbitrary code execution as host root, crossing the container-to-host trust boundary. ### Conditions for exploitation - A user must run a container from a malicious image that contains a trojanized decompression binary. - The user must then upload a compressed archive (xz or gzip) into that container, either by piping a compressed archive via `docker cp -` or by calling the `PUT /containers/{id}/archive` API directly with compressed content. ### Not affected Standard `docker cp` usage is **not** affected, because the CLI sends uncompressed tar by default: ``` docker cp ./file.txt mycontainer:/file.txt ``` This can only be exploited when explicitly passing a xz or gzip-compressed archive to `docker cp` or the `PUT /containers/{id}/archive` API, for example: ``` cat archive.tar.xz | docker cp - mycontainer:/dir ``` Decompression formats using pure Go implementations (bzip2, zstd, and gzip when the container image does not contain an `unpigz` binary) are also not affected. ## Workarounds - Only run containers from trusted images. - Use authorization plugins to limit access to the `PUT /containers/{id}/archive` endpoint. - Avoid piping compressed archives into containers created from untrusted images.

Moby es un framework de contenedor de código abierto. En versiones anteriores a la 29.5.1 y en moby/moby v2 anteriores a la v2.0.0-beta.14, cuando un archivo comprimido se sube a un contenedor a través de 'PUT /containers/{id}/archive' o se canaliza a través de 'docker cp -', el demonio resuelve los binarios de descompresión (como 'xz' o 'unpigz') desde el sistema de archivos del contenedor en lugar del del host debido a un orden incorrecto de las operaciones. Una imagen de contenedor maliciosa que contenga un binario de descompresión troyanizado puede lograr ejecución de código arbitrario con privilegios completos de demonio, incluyendo UID de root del host y capacidades sin restricciones, cuando un usuario sube un archivo comprimido (xz o gzip) a ese contenedor. Este problema está solucionado en Docker Engine 29.5.1 y moby/moby v2.0.0-beta.14. Las soluciones incluyen ejecutar contenedores solo desde imágenes de confianza, usar plugins de autorización para restringir el acceso al endpoint 'PUT /containers/{id}/archive', y evitar canalizar archivos comprimidos a contenedores creados a partir de imágenes no confiables.