Arcane Has an Authenticated Arbitrary Host File Read via Docker Compose Include Directives

Summary

ProjectService.GetProjectFileContent returns the contents of any Docker Compose include directive declared in a project's compose file before any path-traversal validation runs. Because ProjectService.CreateProject writes attacker-supplied compose content to disk without validating include paths, an authenticated user can create a project whose compose file declares include: ['../../../../etc/passwd'], then read the include via the project file API. The result is arbitrary read of any file readable by the Arcane backend process, including /app/data/arcane.db (the SQLite database containing every user's password hash and API key), enabling escalation to admin and, via Arcane's Docker control plane, RCE on the host.

Details

Root cause #1 — CreateProject writes compose content without validation (backend/internal/services/project_service.go:1605-1644):

func (s *ProjectService) CreateProject(ctx context.Context, name, composeContent string, envContent *string, user models.User) (*models.Project, error) {
    // ... directory setup ...
    if err := projects.SaveOrUpdateProjectFiles(projectsDirectory, projectPath, composeContent, envContent); err != nil {
        _ = s.db.WithContext(ctx).Delete(proj).Error
        return nil, fmt.Errorf("failed to save project files: %w", err)
    }
    // ...
}

Compare with UpdateProject (project_service.go:2494, :2577), which calls validateComposeContentForUpdate. That validator (line 2599) loads the compose with missingIncludeStubResourceLoaderInternal, which calls ValidateIncludePathForWrite (includes.go:139) and rejects includes outside the project directory. CreateProject bypasses this entirely, so any malicious include: array survives to disk.

Root cause #2 — GetProjectFileContent reads include files before path validation (backend/internal/services/project_service.go:831-872):

includes, parseErr := projects.ParseIncludes(composeFile, envMap, true)
if parseErr == nil {
    for _, inc := range includes {
        if inc.RelativePath == relativePath {
            return project.IncludeFile{
                Path:         inc.Path,
                RelativePath: inc.RelativePath,
                Content:      inc.Content,    // <-- arbitrary file content returned here
            }, nil
        }
    }
}

fullPath := filepath.Join(proj.Path, relativePath)
// ... IsSafeSubdirectory check at line 870 — never reached when include matches ...

():