GHSA-rrmm-9v76-h3p4 Portainer missing authorization on Docker plugin endpoints, which allows host RCE

• Go github.com/portainer/portainer: >= 2.33.0, < 2.33.8 → fixed in 2.33.8 • Go github.com/portainer/portainer: >= 2.39.0, < 2.39.2 → fixed in 2.39.2 • Go github.com/portainer/portainer: >= 2.40.0, < 2.41.0 → fixed in 2.41.0

Summary Portainer enforces Role-Based Access Control (RBAC) on top of the Docker API. The proxy layer routes incoming Docker API requests to per-resource handlers (containers, images, services, volumes, etc.) that apply authorization checks. The Docker plugin management endpoints (`/plugins/*`) were not registered with a handler, so standard users with endpoint access could call privileged plugin operations — including installing and enabling plugins — directly against the underlying Docker daemon. The vulnerability is exposed when a non-admin Portainer user (Standard User role, or any role granted endpoint-level access) has been given access to a Docker endpoint via Portainer RBAC. Administrators and users without Docker endpoint access are not affected. A regular user with access to a Docker endpoint can: • Pull an arbitrary plugin from any registry via `POST /plugins/pull`. • Grant it the privileges it requests, including `CAP_SYS_ADMIN` and host-path mounts. • Enable the plugin via `POST /plugins/{name}/enable`, at which point Docker runs the plugin with root privileges on the host. Docker plugins execute as root on the host and can request arbitrary host capabilities and mounts. Enabling a crafted plugin gives the user access to the host filesystem and equivalent to root on the Docker host. Severity Critical — CVSS 9.4 `CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H` CWE-862 — Missing Authorization Affected Versions The vulnerability exists in every Portainer release where the Docker API proxy uses the prefix-allowlist routing model — `/plugins` has never been in the allowlist, and the fall-through path has never applied authorization. Fixes are included in the next release of each supported branch: | Branch | First vulnerable | Fixed in | |---------------------|------------------|------------| | 2.33.x (LTS) | 2.33.0 | 2.33.8 | | 2.39.x (LTS) | 2.39.0 | 2.39.2 | | 2.40.x (STS) | 2.40.0 | 2.41.0 | Portainer LTS branches receive fixes for 6 months plus a 3-month overlap after the next LTS ships. STS releases are supported only until the next STS ships — the 2.40.x STS line ends with the 2.41.0 release. All releases prior to 2.33.0 are end-of-life and will not receive a fix; users on EOL versions should upgrade to a supported LTS branch. Workarounds Administrators who cannot immediately upgrade can reduce exposure by temporarily revoking Docker endpoint access for non-admin users via Portainer RBAC until the patched release is deployed. This eliminates the attack surface without disruption for administrators. This does not replace the fix. Affected Code ```go // api/http/proxy/factory/docker/transport.go (pre-fix) var prefixProxyFuncMap = map[string]func(...){ "build": ..., "configs": ..., "containers": ..., "images": ..., "networks": ..., "nodes": ..., "secrets": ..., "services": ..., "swarm": ..., "tasks": ..., "v2": ..., "volumes": ..., } func (transport *Transport) ProxyDockerRequest(request *http.Request) (*http.Response, error) { // ... prefix := strings.Split(strings.TrimPrefix(unversionedPath, "/"), "/")[0] if proxyFunc := prefixProxyFuncMap[prefix]; proxyFunc != nil { return proxyFunc(transport, request, unversionedPath) // authorized } return transport.executeDockerRequest(request) // forwarded without authorization } ``` `/plugins` is not in `prefixProxyFuncMap`, so requests to plugin endpoints fall through to `executeDockerRequest` and are forwarded to the Docker daemon without any Portainer-side authorization check. Impact An authenticated, non-admin Portainer user with access to any Docker-enabled endpoint can: • Install and enable arbitrary Docker plugins from any registry. • Execute plugin code with root privileges on the Docker host (including declaring `CAP_SYS_ADMIN` and host-path mounts). • Read and modify files on the host filesystem from a restricted account, overriding the administrator's security policy. Timeline • 2026-03-16: Reported via GitHub Security Advisory by ikkebr. • 2026-04-20: Fix merged to `develop`, `release/2.39`, and `release/2.33`. • 2026-04-29: 2.41.0 released. • 2026-05-07: 2.39.2-LTS and 2.33.8-LTS released. Credit • ikkebr — identified and reported the proxy allowlist bypass affecting the Docker plugin management endpoints.