diff --git a/src/backend/controllers/fs/FSController.ts b/src/backend/controllers/fs/FSController.ts
index be8fec23d..917e8ee05 100644
--- a/src/backend/controllers/fs/FSController.ts
+++ b/src/backend/controllers/fs/FSController.ts
@@ -20,6 +20,7 @@
 import Busboy from 'busboy';
 import type { Request, Response } from 'express';
 import { posix as pathPosix } from 'node:path';
+import { assertNormalized } from '../../services/fs/resolveNode.js';
 import { pipeline } from 'node:stream/promises';
 import type { Actor } from '../../core/actor.js';
 import { Context } from '../../core/context.js';
@@ -1787,7 +1788,8 @@ export class FSController extends PuterController {
             pathToNormalize = `/${username}${pathToNormalize.slice(1)}`;
         }
 
-        let normalizedPath = pathPosix.normalize(pathToNormalize);
+        assertNormalized(pathToNormalize);
+        let normalizedPath = pathToNormalize;
         if (!normalizedPath.startsWith('/')) {
             normalizedPath = `/${normalizedPath}`;
         }
diff --git a/src/backend/core/http/middleware/hostRedirects.ts b/src/backend/core/http/middleware/hostRedirects.ts
index d2cb0b99a..91f4039a5 100644
--- a/src/backend/core/http/middleware/hostRedirects.ts
+++ b/src/backend/core/http/middleware/hostRedirects.ts
@@ -21,6 +21,7 @@ import type { RequestHandler } from 'express';
 import { stat } from 'node:fs/promises';
 import path from 'node:path';
 import type { IConfig } from '../../../types';
+import { assertNormalized } from '../../../services/fs/resolveNode.js';
 
 /** Native-app subdomains served via `nativeAppStatic`. */
 const NATIVE_APP_SUBDOMAINS = [
@@ -130,10 +131,8 @@ export const createNativeAppStatic = (config: IConfig): RequestHandler => {
             ? path.join(root, active, 'dist')
             : path.join(root, active);
 
-        // req.path is already url-decoded by express; normalize strips any
-        // `..` segments before sendFile's `root` option enforces its own
-        // traversal guard.
-        const requested = path.normalize(req.path);
+        const requested = req.path;
+        assertNormalized(requested);
         const absolute = path.join(appRoot, requested);
 
         try {
diff --git a/src/backend/drivers/ai-image/ImageGenerationDriver.ts b/src/backend/drivers/ai-image/ImageGenerationDriver.ts
index 20bd9166a..22e66733f 100644
--- a/src/backend/drivers/ai-image/ImageGenerationDriver.ts
+++ b/src/backend/drivers/ai-image/ImageGenerationDriver.ts
@@ -19,6 +19,7 @@
 
 import crypto from 'node:crypto';
 import { posix as pathPosix } from 'node:path';
+import { assertNormalized } from '../../services/fs/resolveNode.js';
 import { Readable } from 'node:stream';
 import { Context } from '../../core/context.js';
 import { HttpError } from '../../core/http/HttpError.js';
@@ -419,7 +420,7 @@ export class ImageGenerationDriver extends PuterDriver {
         if (resolved === '~' || resolved.startsWith('~/')) {
             resolved = `/${username}${resolved.slice(1)}`;
         }
-        resolved = pathPosix.normalize(resolved);
+        assertNormalized(resolved);
         if (!resolved.startsWith('/')) {
             resolved = `/${resolved}`;
         }
diff --git a/src/backend/drivers/ai-video/VideoGenerationDriver.ts b/src/backend/drivers/ai-video/VideoGenerationDriver.ts
index 1219f921f..fc35bac5f 100644
--- a/src/backend/drivers/ai-video/VideoGenerationDriver.ts
+++ b/src/backend/drivers/ai-video/VideoGenerationDriver.ts
@@ -18,6 +18,7 @@
  */
 
 import { posix as pathPosix } from 'node:path';
+import { assertNormalized } from '../../services/fs/resolveNode.js';
 import { Readable } from 'node:stream';
 import { Context } from '../../core/context.js';
 import { HttpError } from '../../core/http/HttpError.js';
@@ -458,7 +459,7 @@ export class VideoGenerationDriver extends PuterDriver {
         if (resolved === '~' || resolved.startsWith('~/')) {
             resolved = `/${username}${resolved.slice(1)}`;
         }
-        resolved = pathPosix.normalize(resolved);
+        assertNormalized(resolved);
         if (!resolved.startsWith('/')) {
             resolved = `/${resolved}`;
         }
diff --git a/src/backend/services/acl/ACLService.ts b/src/backend/services/acl/ACLService.ts
index 07c0aa331..4ccc0f3d3 100644
--- a/src/backend/services/acl/ACLService.ts
+++ b/src/backend/services/acl/ACLService.ts
@@ -112,6 +112,7 @@ export class ACLService extends PuterService {
         if (resource.path === '/') {
             return (PUBLIC_READ_MODES as AclMode[]).includes(mode);
         }
+        const ancestors = await resource.resolveAncestors();
 
         const components = resource.path.slice(1).split('/');
 
@@ -171,7 +172,6 @@ export class ACLService extends PuterService {
             const authorizer = actor.accessToken.issuer;
             if (!(await this.check(authorizer, resource, mode))) return false;
 
-            const ancestors = await resource.resolveAncestors();
             for (const ancestor of ancestors) {
                 const permissions =
                     mode === MANAGE_PERM_PREFIX
@@ -219,7 +219,6 @@ export class ACLService extends PuterService {
         // Fall back to the permission scan: walk ancestors, any hit wins.
         // Widen the scan to all "higher" modes (`write` covers `read`/`list`/
         // `see`, etc.) so granting a stronger mode implies the weaker ones.
-        const ancestors = await resource.resolveAncestors();
         for (const ancestor of ancestors) {
             const permissions =
                 mode === MANAGE_PERM_PREFIX
diff --git a/src/backend/services/fs/FSService.ts b/src/backend/services/fs/FSService.ts
index 44db6064b..ae20c6043 100644
--- a/src/backend/services/fs/FSService.ts
+++ b/src/backend/services/fs/FSService.ts
@@ -18,6 +18,7 @@
  */
 
 import { posix as pathPosix } from 'node:path';
+import { assertNormalized } from './resolveNode.js';
 import { createHash } from 'node:crypto';
 import { Readable, Transform } from 'node:stream';
 import type { TransformCallback } from 'node:stream';
@@ -268,7 +269,8 @@ export class FSService extends PuterService {
             );
         }
 
-        let normalizedPath = pathPosix.normalize(trimmedPath);
+        assertNormalized(trimmedPath);
+        let normalizedPath = trimmedPath;
         if (!normalizedPath.startsWith('/')) {
             normalizedPath = `/${normalizedPath}`;
         }
diff --git a/src/backend/services/fs/resolveNode.ts b/src/backend/services/fs/resolveNode.ts
index 4d063c3d1..f2905ac7a 100644
--- a/src/backend/services/fs/resolveNode.ts
+++ b/src/backend/services/fs/resolveNode.ts
@@ -130,6 +130,15 @@ export function splitParentAndName(absolutePath: string): {
     return { parentPath: parentPath === '.' ? '/' : parentPath, name };
 }
 
+export function assertNormalized(input: string): string {
+    if (pathPosix.normalize(input) !== input) {
+        throw new HttpError(400, 'Invalid path', {
+            legacyCode: 'bad_request',
+        });
+    }
+    return input;
+}
+
 export function normalizeAbsolutePath(path: string): string {
     const trimmed = typeof path === 'string' ? path.trim() : '';
     if (trimmed.length === 0) {
@@ -137,7 +146,8 @@ export function normalizeAbsolutePath(path: string): string {
             legacyCode: 'bad_request',
         });
     }
-    let normalized = pathPosix.normalize(trimmed);
+    assertNormalized(trimmed);
+    let normalized = trimmed;
     if (!normalized.startsWith('/')) {
         normalized = `/${normalized}`;
     }
diff --git a/src/backend/stores/fs/FSEntryStore.ts b/src/backend/stores/fs/FSEntryStore.ts
index ffcccfdfb..28fd29674 100644
--- a/src/backend/stores/fs/FSEntryStore.ts
+++ b/src/backend/stores/fs/FSEntryStore.ts
@@ -19,6 +19,7 @@
 
 import { statfs } from 'node:fs/promises';
 import { posix as pathPosix } from 'node:path';
+import { assertNormalized } from '../../services/fs/resolveNode.js';
 import { v4 as uuidv4 } from 'uuid';
 import { HttpError } from '../../core/http/HttpError.js';
 import type { LayerInstances } from '../../types.js';
@@ -175,7 +176,8 @@ export class FSEntryStore extends PuterStore {
             });
         }
 
-        let normalized = pathPosix.normalize(trimmed);
+        assertNormalized(trimmed);
+        let normalized = trimmed;
         if (!normalized.startsWith('/')) {
             normalized = `/${normalized}`;
         }