fix: nightly hardening - symlink-safe skill config handling

src/cli/commands/skill.ts

@@ -14,7 +14,7 @@
  *   windsurf        Windsurf (~/.codeium/windsurf/mcp_config.json)
  */
 
-import { readFile, writeFile, mkdir, rename, copyFile } from "node:fs/promises"
+import { readFile, writeFile, mkdir, rename, copyFile, lstat } from "node:fs/promises"
 import { existsSync } from "node:fs"
 import { resolve, dirname } from "node:path"
 import { homedir, platform } from "node:os"
@@ -101,6 +101,7 @@ function isToolDetected(tool: ToolDef): boolean {
 
 export async function readJsonConfig(path: string): Promise<Record<string, unknown>> {
   if (!existsSync(path)) return {}
+  await assertSafeConfigPath(path)
   const raw = await readFile(path, "utf-8")
   const normalized = raw.replace(/^\uFEFF/, "").trim()
   if (normalized.length === 0) return {}
@@ -110,13 +111,24 @@ export async function readJsonConfig(path: string): Promise<Record<string, unkno
 export async function writeJsonConfig(path: string, data: Record<string, unknown>): Promise<void> {
   await mkdir(dirname(path), { recursive: true })
   if (existsSync(path)) {
+    await assertSafeConfigPath(path)
     await copyFile(path, path + ".backup")
   }
   const tmp = path + ".tmp"
   await writeFile(tmp, JSON.stringify(data, null, 2) + "\n", "utf-8")
   await rename(tmp, path)
 }
 
+async function assertSafeConfigPath(path: string): Promise<void> {
+  const stats = await lstat(path)
+  if (stats.isSymbolicLink()) {
+    throw new Error(`Refusing to use symlinked config path: ${path}`)
+  }
+  if (!stats.isFile()) {
+    throw new Error(`Config path is not a regular file: ${path}`)
+  }
+}
+
 
 function hasYouMdInstalled(config: Record<string, unknown>, tool: ToolDef): boolean {
   let cur: unknown = config

test/cli/skill.test.ts

@@ -1,6 +1,6 @@
 import { describe, it, expect, beforeEach, afterEach } from "vitest";
 import { join } from "node:path";
-import { mkdirSync, rmSync, writeFileSync, readFileSync, existsSync } from "node:fs";
+import { mkdirSync, rmSync, writeFileSync, readFileSync, existsSync, symlinkSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { readJsonConfig, writeJsonConfig } from "../../src/cli/commands/skill";
 
@@ -52,6 +52,15 @@ describe("readJsonConfig", () => {
     const result = await readJsonConfig(filePath);
     expect(result).toEqual(data);
   });
+
+  it("rejects symlinked config files", async () => {
+    const targetPath = join(tempDir, "target.json");
+    const linkPath = join(tempDir, "link.json");
+    writeFileSync(targetPath, JSON.stringify({ ok: true }), "utf-8");
+    symlinkSync(targetPath, linkPath);
+
+    await expect(readJsonConfig(linkPath)).rejects.toThrow(/symlinked config path/);
+  });
 });
 
 describe("writeJsonConfig", () => {
@@ -105,4 +114,13 @@ describe("writeJsonConfig", () => {
     const content = readFileSync(filePath, "utf-8");
     expect(content).toBe(JSON.stringify(data, null, 2) + "\n");
   });
+
+  it("rejects writing to symlinked config files", async () => {
+    const targetPath = join(tempDir, "target-write.json");
+    const linkPath = join(tempDir, "link-write.json");
+    writeFileSync(targetPath, JSON.stringify({ existing: true }), "utf-8");
+    symlinkSync(targetPath, linkPath);
+
+    await expect(writeJsonConfig(linkPath, { updated: true })).rejects.toThrow(/symlinked config path/);
+  });
 });