GHSA-cqpq-2fgr-8mvc: Portainer missing authorization on custom template file endpoint, which exposes template content
SummaryA missing authorization vulnerability in the Custom Template file endpoint (`GET /api/custom_templates/{id}/file`) allows any authenticated user to read the file content of any custom template by enumerating sequential integer IDs, bypassing Resource Control access restrictions. Template files may contain environment-specific values such as connection strings, API tokens, or registry credentials that administrators would not expect standard users to read.Severity**Medium****CWE-862** — Missing AuthorizationExploitation requires an authenticated user account and at least one custom template to exist. Template files are returned verbatim and may contain embedded credentials.Affected VersionsThe vulnerability exists in every Portainer release since custom templates were introduced — the `customTemplateFile` handler has never performed an authorization check.Fixes are included in the following releases:| Branch              | First vulnerable | Fixed in   |
|---------------------|------------------|------------|
| 2.33.x (LTS)        | 2.33.0           | **2.33.8** |
| 2.39.x (LTS)        | 2.39.0           | **2.39.1** |Portainer 2.40.0 and later are not affected — the fix was already on `develop` when the 2.40.x STS line branched. Portainer LTS branches receive fixes for 6 months plus a 3-month overlap after the next LTS ships. 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 release.WorkaroundsThere is no runtime configuration that blocks the vulnerable endpoint directly. Administrators who cannot immediately upgrade can reduce exposure by:**Avoiding storing secrets in custom templates** until the patched release is deployed. Move sensitive configuration values to Portainer environment variables or an external secret store.**Reviewing existing custom templates** for embedded secrets. Assume any secret previously stored in a custom template on an unpatched instance has been exposed to every authenticated user and rotate accordingly.Neither replaces the fix.Affected CodeThe `customTemplateFile` handler in `api/http/handler/customtemplates/customtemplate_file.go` (lines 30-53) retrieves a custom template by its numeric ID and returns the file content without performing any authorization check.All other custom template endpoints properly verify access:| Endpoint | Method | Authorization Check |
|----------|--------|-------------------|
| `/api/custom_templates/{id}` | GET (inspect) | `userCanEditTemplate()` + `UserCanAccessResource()` |
| `/api/custom_templates/{id}` | PUT (update) | `userCanEditTemplate()` |
| `/api/custom_templates/{id}` | DELETE | `userCanEditTemplate()` |
| `/api/custom_templates` | GET (list) | `FilterAuthorizedCustomTemplates()` |
| **`/api/custom_templates/{id}/file`** | **GET** | **None** |**Vulnerable code** (`customtemplate_file.go:30-53`):**Secure reference** (`customtemplate_inspect.go:50-75`):ImpactAny authenticated user (including the lowest-privilege standard user) can read the file content of every custom template in the instance. Custom templates commonly contain Docker Compose configuration, which may include environment-specific secrets such as database connection strings, API tokens, or registry credentials.Timeline2026-02-11: Reported via GitHub Security Advisory by **duddnr0615k**.2026-03-04: Fix merged to `develop` and cherry-picked to `release/2.39`.2026-03-19: 2.39.1 released with fix.2026-03-25: 2.40.0 released with fix already present from branch cut.2026-05-07: 2.33.8 released.Credit**duddnr0615k** — identified and reported the missing authorization check on the custom template file endpoint.
CVSS v4.0: 6
CVSS v3.1: 6.5