fix(security): block hook transform symlink escapes

src/gateway/hooks-mapping.ts

@@ -1,3 +1,4 @@
+import fs from "node:fs";
 import path from "node:path";
 import { CONFIG_PATH, type HookMappingConfig, type HooksConfig } from "../config/config.js";
 import { importFileModule, resolveFunctionModuleExport } from "../hooks/module-loader.js";
@@ -355,6 +356,34 @@ function resolvePath(baseDir: string, target: string): string {
   return path.isAbsolute(target) ? path.resolve(target) : path.resolve(baseDir, target);
 }
 
+function escapesBase(baseDir: string, candidate: string): boolean {
+  const relative = path.relative(baseDir, candidate);
+  return relative === ".." || relative.startsWith(`..${path.sep}`) || path.isAbsolute(relative);
+}
+
+function safeRealpathSync(candidate: string): string | null {
+  try {
+    const nativeRealpath = fs.realpathSync.native as ((path: string) => string) | undefined;
+    return nativeRealpath ? nativeRealpath(candidate) : fs.realpathSync(candidate);
+  } catch {
+    return null;
+  }
+}
+
+function resolveExistingAncestor(candidate: string): string | null {
+  let current = path.resolve(candidate);
+  while (true) {
+    if (fs.existsSync(current)) {
+      return current;
+    }
+    const parent = path.dirname(current);
+    if (parent === current) {
+      return null;
+    }
+    current = parent;
+  }
+}
+
 function resolveContainedPath(baseDir: string, target: string, label: string): string {
   const base = path.resolve(baseDir);
   const trimmed = target?.trim();
@@ -362,8 +391,20 @@ function resolveContainedPath(baseDir: string, target: string, label: string): s
     throw new Error(`${label} module path is required`);
   }
   const resolved = resolvePath(base, trimmed);
-  const relative = path.relative(base, resolved);
-  if (relative === ".." || relative.startsWith(`..${path.sep}`) || path.isAbsolute(relative)) {
+  if (escapesBase(base, resolved)) {
+    throw new Error(`${label} module path must be within ${base}: ${target}`);
+  }
+
+  // Block symlink escapes for existing path segments while preserving current
+  // behavior for not-yet-created files.
+  const baseRealpath = safeRealpathSync(base);
+  const existingAncestor = resolveExistingAncestor(resolved);
+  const existingAncestorRealpath = existingAncestor ? safeRealpathSync(existingAncestor) : null;
+  if (
+    baseRealpath &&
+    existingAncestorRealpath &&
+    escapesBase(baseRealpath, existingAncestorRealpath)
+  ) {
     throw new Error(`${label} module path must be within ${base}: ${target}`);
   }
   return resolved;