🛡️ Sentinel: [CRITICAL] Fix path traversal in export command

.jules/sentinel.md

@@ -0,0 +1,4 @@
+## 2024-06-16 - Prevent Path Traversal in Export Path
+**Vulnerability:** The `exportGherkin` command accepted arbitrary paths via the `--output` option and concatenated them with the project root using `join()`, allowing path traversal (e.g., `../../../../tmp/hacked.feature`) to write files outside the intended project directory boundaries.
+**Learning:** In CLI applications that write to user-specified paths, using `join()` alone is insufficient for preventing traversal attacks. Path boundaries must be explicitly validated.
+**Prevention:** Always use `resolve()` to compute the absolute target path, use `relative(root, target)` to calculate the distance, and check for `..`, `startsWith(".." + sep)`, or `isAbsolute(rel)` to ensure the resolved path stays within the intended directory boundary.

src/export/gherkin.ts

@@ -1,5 +1,6 @@
 import { mkdirSync, readFileSync, writeFileSync } from "node:fs";
-import { dirname, join } from "node:path";
+import { dirname, isAbsolute, join, relative, resolve, sep } from "node:path";
+import { VspecError } from "../errors.js";
 import { findUseCaseFile, readConfig, relativePath } from "../files.js";
 import { parseUseCaseMarkdown } from "../format/parse.js";
 import type { ParsedUseCase } from "../domain/types.js";
@@ -39,7 +40,11 @@ export function exportGherkin(args: { key: string; output?: string; cwd?: string
   if (!source) throw new Error("KEY_NOT_FOUND");
   const text = renderGherkin(parseUseCaseMarkdown(readFileSync(source, "utf8")));
   const output = args.output ?? join("tests", `${args.key}.feature`);
-  const outputPath = join(config.root, output);
+  const outputPath = resolve(config.root, output);
+  const rel = relative(config.root, outputPath);
+  if (rel === ".." || rel.startsWith(".." + sep) || isAbsolute(rel)) {
+    throw new VspecError("INVALID_ARGUMENT", "Invalid output path: Path traversal detected.");
+  }
   mkdirSync(dirname(outputPath), { recursive: true });
   writeFileSync(outputPath, text);
   return { key: args.key, text, path: relativePath(outputPath, config.root) };

tests/gherkin-security.test.ts

@@ -0,0 +1,49 @@
+import { join } from "node:path";
+import { describe, expect, it, beforeEach, afterEach } from "vitest";
+import { mkdirSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { randomUUID } from "node:crypto";
+import { exportGherkin } from "../src/export/gherkin.js";
+import { initProject } from "../src/project.js";
+
+describe("gherkin security", () => {
+  let cwd: string;
+
+  beforeEach(() => {
+    cwd = join(tmpdir(), randomUUID());
+    mkdirSync(cwd, { recursive: true });
+    initProject({ key: "TEST", root: cwd });
+    mkdirSync(join(cwd, "specs/usecases"), { recursive: true });
+
+    // Create a dummy use case file
+    const md = `---
+vspec_format: 1
+type: usecase
+key: TEST-001
+title: Test use case
+scope: test_project
+level: USER_GOAL
+primary_actor: system
+priority: P1
+status: DRAFT
+format: BRIEF
+---
+`;
+    writeFileSync(join(cwd, "specs/usecases/TEST-001-test.md"), md);
+  });
+
+  afterEach(() => {
+    rmSync(cwd, { recursive: true, force: true });
+  });
+
+  it("prevents path traversal in output path", () => {
+    expect(() =>
+      exportGherkin({ key: "TEST-001", output: "../../../../../tmp/hacked.feature", cwd })
+    ).toThrowError("Invalid output path: Path traversal detected.");
+  });
+
+  it("allows valid output paths inside the project", () => {
+    const result = exportGherkin({ key: "TEST-001", output: "tests/valid.feature", cwd });
+    expect(result.path).toBe("tests/valid.feature");
+  });
+});