diff --git a/src/app/api/audiobook/route.ts b/src/app/api/audiobook/route.ts
index d2e639d..9d6d0f3 100644
--- a/src/app/api/audiobook/route.ts
+++ b/src/app/api/audiobook/route.ts
@@ -2,7 +2,7 @@ import { NextRequest, NextResponse } from 'next/server';
 import { spawn } from 'child_process';
 import { readFile, writeFile, mkdir, unlink, rm, rename, readdir } from 'fs/promises';
 import { existsSync, createReadStream } from 'fs';
-import { basename, join } from 'path';
+import { basename, join, resolve } from 'path';
 import { randomUUID } from 'crypto';
 import { AUDIOBOOKS_V1_DIR, isAudiobooksV1Ready } from '@/lib/server/docstore';
 import { encodeChapterFileName, encodeChapterTitleTag, listStoredChapters, ffprobeAudio } from '@/lib/server/audiobook';
@@ -15,7 +15,14 @@ function getAudiobooksRootDir(request: NextRequest): string {
   const raw = request.headers.get('x-openreader-test-namespace')?.trim();
   if (!raw) return AUDIOBOOKS_V1_DIR;
   const safe = raw.replace(/[^a-zA-Z0-9._-]/g, '');
-  return safe ? join(AUDIOBOOKS_V1_DIR, safe) : AUDIOBOOKS_V1_DIR;
+  if (!safe || safe === '.' || safe === '..' || safe.includes('..')) {
+    return AUDIOBOOKS_V1_DIR;
+  }
+  const resolved = resolve(AUDIOBOOKS_V1_DIR, safe);
+  if (!resolved.startsWith(resolve(AUDIOBOOKS_V1_DIR) + '/')) {
+    return AUDIOBOOKS_V1_DIR;
+  }
+  return resolved;
 }
 
 interface ConversionRequest {
diff --git a/tests/docstore_unit.spec.ts b/tests/docstore_unit.spec.ts
index fda3d92..ccd4879 100644
--- a/tests/docstore_unit.spec.ts
+++ b/tests/docstore_unit.spec.ts
@@ -26,13 +26,11 @@ test.describe('Docstore Filename Safety', () => {
     const result = getMigratedDocumentFileName(id, specialName);
     
     expect(result.length).toBeLessThanOrEqual(240);
-    if (result.includes('truncated-')) {
-        expect(result).toContain('truncated-');
-    } else {
-        // If it fits (depends on length), just ensure it is valid
-        // 30 * 4 = 120 chars raw, but encoded?
-        // Let's ensure logic works.
-    }
+    expect(result).toContain('truncated-');
+    // The implementation replaces the name with a hash, so it should NOT contain the original special chars
+    // and might not contain % if the hash is hex.
+    expect(result).toMatch(/truncated-[a-f0-9]{32}$/);
+    expect(result.startsWith(`${id}__`)).toBeTruthy();
   });
 
   test('should handle edge case length exactly', () => {