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.
References
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}/archiverequests 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
docker cp -or by calling thePUT /containers/{id}/archiveAPI directly with compressed content.Not affected
Standard
docker cpusage is not affected, because the CLI sends uncompressed tar by default:This can only be exploited when explicitly passing a xz or gzip-compressed archive to
docker cpor thePUT /containers/{id}/archiveAPI, for example:Decompression formats using pure Go implementations (bzip2, zstd, and gzip when the container image does not contain an
unpigzbinary) are also not affected.Workarounds
PUT /containers/{id}/archiveendpoint.References