CVE-2026-44884

Description

## Summary A 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 Authorization Exploitation requires an authenticated user account and at least one custom template to exist. Template files are returned verbatim and may contain embedded credentials. ## Affected Versions The 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. ## Workarounds There 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 Code The `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`): ```go func (handler *Handler) customTemplateFile(w http.ResponseWriter, r *http.Request) *httperror.HandlerError { customTemplateID, _ := request.RetrieveNumericRouteVariableValue(r, "id") customTemplate, _ := handler.DataStore.CustomTemplate().Read(portainer.CustomTemplateID(customTemplateID)) // NO AUTHORIZATION CHECK fileContent, _ := handler.FileService.GetFileContent(customTemplate.ProjectPath, entryPath) return response.JSON(w, &fileResponse{FileContent: string(fileContent)}) } ``` **Secure reference** (`customtemplate_inspect.go:50-75`): ```go canEdit := userCanEditTemplate(customTemplate, securityContext) hasAccess := authorization.UserCanAccessResource(securityContext.UserID, teamIDs, resourceControl) if !canEdit && !hasAccess { return httperror.Forbidden("Access denied to resource", httperrors.ErrResourceAccessDenied) } ``` ## Impact Any 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. ## Timeline - 2026-02-11: 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.