Summary

The PUT /api/environments/{id}/templates/variables endpoint, which writes the system-wide .env.global file used for variable substitution in every project's compose file, is missing an admin authorization check. Any authenticated non-admin user can call this endpoint with their bearer token or API key and overwrite the global environment variables that are merged into every project deployment. By overriding values like REGISTRY, IMAGE, DATABASE_URL, or SECRET_KEY that other users reference via ${VAR} in compose files, an attacker can redirect image pulls to attacker-controlled registries (supply-chain RCE on the Docker host), exfiltrate database credentials, or disrupt all projects.

Details

The endpoint is registered at backend/internal/huma/handlers/templates.go:374:

huma.Register(api, huma.Operation{
    OperationID: "updateGlobalVariables",
    Method:      "PUT",
    Path:        "/environments/{id}/templates/variables",
    ...
    Security: []map[string][]string{
        {"BearerAuth": {}},
        {"ApiKeyAuth": {}},
    },
}, h.UpdateGlobalVariables)

The handler at backend/internal/huma/handlers/templates.go:889 performs no role check:

func (h *TemplateHandler) UpdateGlobalVariables(ctx context.Context, input *UpdateGlobalVariablesInput) (*UpdateGlobalVariablesOutput, error) {
    if h.templateService == nil {
        return nil, huma.Error500InternalServerError("service not available")
    }

    if input.EnvironmentID != "0" {
        return h.updateGlobalVariablesForRemoteEnvironmentInternal(ctx, input)
    }

    if err := h.templateService.UpdateGlobalVariables(ctx, input.Body.Variables); err != nil {
        return nil, huma.Error500InternalServerError((&common.GlobalVariablesUpdateError{Err: err}).Error())
    }
    ...
}

This is anomalous compared to every other admin-sensitive handler in the codebase, all of which begin with if err := checkAdmin(ctx); err != nil { return nil, err } (see users.go, events.go, swarm.go, settings.go, apikeys.go, environments.go, notifications.go, container_registries.go, git_repositories.go, system.go). The helper exists at backend/internal/huma/handlers/helpers.go:12 but is never invoked from templates.go.

The auth middleware at backend/internal/huma/middleware/auth.go:192-254 only validates that some authenticated user is present (Bearer JWT, API key, or environment access token); it does not enforce roles. Role enforcement is the responsibility of each handler.

That this endpoint is intended to be admin-only is evidenced by the UI customization search at backend/internal/huma/handlers/customize.go:82-91 and :106-114, which explicitly hides the variables and registries categories from non-admin users:

if !humamw.IsAdminFromContext(ctx) {
    filtered := []category.Category{}
    for _, cat := range results.Results {
        if cat.ID != "registries" && cat.ID != "variables" {
            filtered = append(filtered, cat)
        }
    }
    results.Results = filtered
    ...
}

The corresponding container_registries.go handlers all enforce admin via checkAdmin() (e.g. container_registries.go:273,329,360,387,442); the equivalent enforcement for the global-variables write was forgotten.

The service layer at backend/internal/services/template_service.go:1107 writes attacker-supplied keys/values to <projectsDirectory>/.env.global:

func (s *TemplateService) UpdateGlobalVariables(ctx context.Context, vars []env.Variable) error {
    envPath, err := s.getGlobalVariablesPath(ctx)
    ...
    for _, v := range vars {
        if strings.TrimSpace(v.Key) == "" { continue }
        key := strings.TrimSpace(v.Key)
        value := strings.TrimSpace(v.Value)
        if strings.ContainsAny(value, " \t\n\r#") {
            value = fmt.Sprintf(`"%s"`, strings.ReplaceAll(value, `"`, `\"`))
        }
        _, _ = fmt.Fprintf(&builder, "%s=%s\n", key, value)
    }
    if err := projects.WriteFileWithPerm(envPath, builder.String(), common.FilePerm); err != nil { ... }
}

That file is then loaded for every project at deploy time via backend/pkg/projects/env.go:65-82 (EnvLoader.LoadEnvironment → loadAndMergeGlobalEnv):

if strings.TrimSpace(l.projectsDir) != "" {
    globalEnvPath := filepath.Join(l.projectsDir, GlobalEnvFileName)
    if err := l.loadAndMergeGlobalEnv(ctx, globalEnvPath, envMap, injectionVars); err != nil ...
}

loadAndMergeGlobalEnv (env.go:94-125) populates both envMap (used by compose-go for ${VAR} substitution in compose files) and injectionVars (auto-injected into containers). The result: a single non-admin write to the global variables endpoint changes the resolved compose state of every project on the host.

Additionally, the key field is only strings.TrimSpace'd (template_service.go:1128); embedded newlines inside the key are not removed, so a key like "FOO\nINJECTED" will write two lines into .env.global, allowing arbitrary key injection and overwrite of variables an attacker did not include in their request body.

Impact

• Cross-project supply-chain RCE on the Docker host. Compose files commonly reference ${REGISTRY}/${IMAGE}:${TAG}. By pointing REGISTRY (or IMAGE) at an attacker-controlled registry, the next deploy of any affected project pulls and runs attacker code with whatever privileges Arcane gives that container (commonly Docker socket access, host volume mounts, etc.).
• Credential theft from other users' projects. Variables like DATABASE_URL, SMTP_HOST, WEBHOOK_URL, S3_ENDPOINT can be redirected to attacker-controlled servers; the next deploy will hand the new connection strings to applications that then submit credentials/data to the attacker.
• Cross-tenant integrity and availability. A single non-admin user can corrupt .env.global to break every project on the instance.
• Bypass of intended privilege boundary. The UI explicitly hides the variables and registries surfaces from non-admins, indicating these are admin-only controls; this finding closes the gap between the documented privilege model and the API enforcement.

The privilege delta is significant: the project clearly distinguishes admin from non-admin users (separate roles, admin-only UI categories, checkAdmin() enforced on dozens of other endpoints), yet this endpoint grants a non-admin the ability to execute attacker-controlled images on the host on behalf of every other tenant.

References

• GHSA-jpjh-jm2p-39hh