Executive brief
Portainer is a management platform used to simplify the deployment and monitoring of containerized applications like Kubernetes. A flaw in its security checks allows a logged-in user to bypass internal authorization and access Kubernetes clusters they are not supposed to manage. This could allow an attacker to view sensitive data, modify application deployments, or gain further access to the corporate infrastructure.
Technical details
An incorrect authorization vulnerability (CWE-863) exists in Portainer's 'kubeClientMiddleware' within 'api/http/handler/kubernetes/handler.go'. When 'security.RetrieveTokenData' returns an error, the middleware writes an HTTP 403 error response but lacks a 'return' statement, allowing execution to continue with a nil 'tokenData' value. This results in the request being forwarded to the Kubernetes cluster proxy regardless of the failed validation. An attacker with a valid Portainer session can exploit this to read or modify namespaced resources (pods, secrets, config maps) on Kubernetes environments they are not authorized to access. The issue is fixed in versions 2.33.8 and 2.39.0.
Affected products
- Portainer Portainer CE >= 2.33.0, < 2.33.8; < 2.39.0
- Portainer Portainer EE >= 2.33.0, < 2.33.8; < 2.39.0
Timeline
- 2026-02-16: patched: Fix merged to develop branch
- 2026-02-25: advisory: Version 2.39.0 released with fix
- 2026-05-07: advisory: Version 2.33.8 released with backported fix
- 2026-05-14: disclosed: GitHub Advisory published
References
- https://api.github.com/users/kolega-ai-dev
- https://github.com/kolega-ai-dev
- https://api.github.com/users/kolega-ai-dev/gists%7B/gist_id%7D
- https://api.github.com/users/kolega-ai-dev/repos
- https://avatars.githubusercontent.com/u/250560052?v=4
- https://api.github.com/users/kolega-ai-dev/events%7B/privacy%7D