Awesome
whoc
A container image that extracts the underlying container runtime and sends it to a remote server. Poke at the underlying container runtime of your favorite CSP container platform!
- WhoC at Defcon 29 Cloud Village
- Azurescape - whoc-powered research, the first cross-account container takeover in the public cloud (70,000$ bounty)
How does it work?
As shown by runc CVE-2019-5736, traditional Linux container runtimes expose themselves to the containers they're running through /proc/self/exe
. whoc
uses this link to read the container runtime executing it.
Dynamic Mode
This is whoc
default mode that works against dynamically linked container runtimes.
- The
whoc
image entrypoint is set to/proc/self/exe
, and the image's dynamic linker (ld.so
) is replaced withupload_runtime
. - Once the image is run, the container runtime re-executes itself inside the container.
- Given the runtime is dynamically linked, the kernel loads our fake dynamic linker (
upload_runtime
) to the runtime process and passes execution to it. upload_runtime
reads the runtime binary through/proc/self/exe
and sends it to the configured remote server.
Wait-For-Exec Mode
For statically linked container runtimes, whoc
comes in another flavor: whoc:waitforexec
.
upload_runtime
is the image entrypoint, and runs as thewhoc
container PID 1.- The user is expected to exec into the
whoc
container and invoke a file pointing to/proc/self/exe
(e.g.docker exec whoc_ctr /proc/self/exe
). - Once the exec occurs, the container runtime re-executes itself inside the container.
upload_runtime
reads the runtime binary through/proc/$runtime-pid/exe
and sends it to the configured remote server.
Try Locally
You'll need docker
and python3
installed. Clone the repository:
git clone git@github.com:twistlock/whoc.git && cd whoc
Set up a file server to receive the extracted container runtime:
mkdir -p stash && cd stash
ln -s ../util/fileserver.py fileserver
./fileserver
From another shell, run the whoc
image in your container environment of choice, for example Docker:
cd whoc
docker build -f Dockerfile_dynamic -t whoc:latest src # or ./util/build.sh
docker run --rm -it --net=host whoc:latest 127.0.0.1 # or ./util/run_local.sh
See that the file server received the container runtime. If you run whoc
under vanilla Docker, the received container runtime should be runc.
--net=host
is only used in local tests so that the whoc
container could easily reach the fileserver on the host via 127.0.0.1
.
Other Platforms
By default whoc
is built for linux/amd64
, but it also supports other CPU architectures. Wait-for-exec mode can be built as usual. To build whoc
in dynamic mode for other CPU architectures, you must populate the PLATFORM_LD_PATH_ARG
build argument with the path of the dynamic linker on the target architecture.
An example build script for arm64
is available at util/build_arm64.sh
.
Help
Help for whoc
's main binary, upload_runtime
:
Usage: upload_runtime [options] <server_ip>
Options:
-p, --port Port of remote server, defaults to 8080
-e, --exec Wait-for-exec mode for static container runtimes, waits until an exec to the container occurred
-b, --exec-bin In exec mode, overrides the default binary created for the exec, default is /bin/enter
-a, --exec-extra-argument In exec mode, pass an additional argument to the runtime so it won't exit quickly
-r, --exec-readdir-proc In exec mode, instead of guessing the runtime pid (which gives whoc one shot of catching the runtime),
find the runtime by searching for new processes under '/proc'