fix(langchain): Fix local file store traversal issue

docs/core_docs/docs/integrations/stores/file_system.ipynb

@@ -46,6 +46,14 @@
     "\n",
     ":::\n",
     "\n",
+    ":::warning\n",
+    "\n",
+    "\n",
+    "This file store can alter any text file in the provided directory and any subfolders.\n",
+    "Make sure that the path you specify when initializing the store is free of other files.\n",
+    "\n",
+    ":::\n",
+    "\n",
     "```\n",
     "\n",
     "### Integration details\n",

langchain/src/storage/file_system.ts

@@ -26,6 +26,11 @@ import { BaseStore } from "@langchain/core/stores";
  *   await store.mdelete([key]);
  * }
  * ```
+ *
+ * @security **Security Notice** This file store
+ * can alter any text file in the provided directory and any subfolders.
+ * Make sure that the path you specify when initializing the store is free
+ * of other files.
  */
 export class LocalFileStore extends BaseStore<string, Uint8Array> {
   lc_namespace = ["langchain", "storage"];
@@ -43,6 +48,12 @@ export class LocalFileStore extends BaseStore<string, Uint8Array> {
    * @returns Promise that resolves to the parsed file content.
    */
   private async getParsedFile(key: string): Promise<Uint8Array | undefined> {
+    // Validate the key to prevent path traversal
+    if (!/^[a-zA-Z0-9_\-:.]+$/.test(key)) {
+      throw new Error(
+        "Invalid key. Only alphanumeric characters, underscores, hyphens, colons, and periods are allowed."
+      );
+    }
     try {
       const fileContent = await fs.readFile(this.getFullPath(key));
       if (!fileContent) {
@@ -87,11 +98,26 @@ export class LocalFileStore extends BaseStore<string, Uint8Array> {
   private getFullPath(key: string): string {
     try {
       const keyAsTxtFile = `${key}.txt`;
-      const fullPath = path.join(this.rootPath, keyAsTxtFile);
+
+      // Validate the key to prevent path traversal
+      if (!/^[a-zA-Z0-9_.\-/]+$/.test(key)) {
+        throw new Error(`Invalid characters in key: ${key}`);
+      }
+
+      const fullPath = path.resolve(this.rootPath, keyAsTxtFile);
+      const commonPath = path.resolve(this.rootPath);
+
+      if (!fullPath.startsWith(commonPath)) {
+        throw new Error(
+          `Invalid key: ${key}. Key should be relative to the root path. ` +
+            `Root path: ${this.rootPath}, Full path: ${fullPath}`
+        );
+      }
+
       return fullPath;
     } catch (e) {
       throw new Error(
-        `Error getting full path for key: ${key}.\nError: ${JSON.stringify(e)}`
+        `Error getting full path for key: ${key}.\nError: ${String(e)}`
       );
     }
   }

langchain/src/storage/tests/file_system.test.ts

@@ -88,4 +88,23 @@ describe("LocalFileStore", () => {
     ).toEqual([value1, value2]);
     await fs.promises.rm(secondaryRootPath, { recursive: true, force: true });
   });
+
+  test("Should disallow attempts to traverse paths outside of a subfolder", async () => {
+    const encoder = new TextEncoder();
+    const store = await LocalFileStore.fromPath(secondaryRootPath);
+    const value1 = new Date().toISOString();
+    await expect(
+      store.mset([["../foo", encoder.encode(value1)]])
+    ).rejects.toThrowError();
+    await expect(
+      store.mset([["/foo", encoder.encode(value1)]])
+    ).rejects.toThrowError();
+    await expect(
+      store.mset([["\\foo", encoder.encode(value1)]])
+    ).rejects.toThrowError();
+    await expect(store.mget(["../foo"])).rejects.toThrowError();
+    await expect(store.mget(["/foo"])).rejects.toThrowError();
+    await expect(store.mget(["\\foo"])).rejects.toThrowError();
+    await fs.promises.rm(secondaryRootPath, { recursive: true, force: true });
+  });
 });