diff --git a/apps/server/src/core/attachment/attachment.controller.ts b/apps/server/src/core/attachment/attachment.controller.ts
index 7b24cc35..784e527e 100644
--- a/apps/server/src/core/attachment/attachment.controller.ts
+++ b/apps/server/src/core/attachment/attachment.controller.ts
@@ -53,6 +53,7 @@ import { EnvironmentService } from '../../integrations/environment/environment.s
 import { TokenService } from '../auth/services/token.service';
 import { JwtAttachmentPayload, JwtType } from '../auth/dto/jwt-payload';
 import * as path from 'path';
+import { sanitize } from 'sanitize-filename-ts';
 import { AttachmentInfoDto, RemoveIconDto } from './dto/attachment.dto';
 import { PageAccessService } from '../page/page-access/page-access.service';
 import { AuditEvent, AuditResource } from '../../common/events/audit-events';
@@ -356,6 +357,10 @@ export class AttachmentController {
       throw new BadRequestException('Invalid image attachment type');
     }
 
+    if (!fileName || sanitize(fileName) !== fileName) {
+      throw new BadRequestException('Invalid file name');
+    }
+
     const filenameWithoutExt = path.basename(fileName, path.extname(fileName));
     if (!isValidUUID(filenameWithoutExt)) {
       throw new BadRequestException('Invalid file id');
diff --git a/apps/server/src/integrations/storage/drivers/local.driver.spec.ts b/apps/server/src/integrations/storage/drivers/local.driver.spec.ts
new file mode 100644
index 00000000..ccdddcc5
--- /dev/null
+++ b/apps/server/src/integrations/storage/drivers/local.driver.spec.ts
@@ -0,0 +1,67 @@
+import { resolve, sep } from 'path';
+import { LocalDriver } from './local.driver';
+
+type FullPath = (filePath: string) => string;
+
+describe('LocalDriver._fullPath', () => {
+  const ROOT = resolve('/data/storage');
+  const driver = new LocalDriver({ storagePath: ROOT });
+  const fullPath = ((driver as any)._fullPath as FullPath).bind(driver);
+
+  describe('legitimate inputs (behavior preserved)', () => {
+    it.each([
+      ['workspace-id/avatars/uuid.png', `${ROOT}${sep}workspace-id${sep}avatars${sep}uuid.png`],
+      ['workspace-id/files/uuid/file.pdf', `${ROOT}${sep}workspace-id${sep}files${sep}uuid${sep}file.pdf`],
+      ['a/b/c/d/e.bin', `${ROOT}${sep}a${sep}b${sep}c${sep}d${sep}e.bin`],
+      ['', ROOT],
+      ['.', ROOT],
+      ['./x/y.png', `${ROOT}${sep}x${sep}y.png`],
+      ['a//b', `${ROOT}${sep}a${sep}b`],
+      ['a/b/../c', `${ROOT}${sep}a${sep}c`],
+    ])('resolves %j to %j', (input, expected) => {
+      expect(fullPath(input)).toBe(expected);
+    });
+  });
+
+  describe('traversal rejected', () => {
+    it.each([
+      '../etc/passwd',
+      '../../../etc/passwd',
+      'workspace/../../../etc/passwd',
+      '..',
+      '../..',
+      'a/../../..',
+    ])('throws for %j', (input) => {
+      expect(() => fullPath(input)).toThrow('Invalid file path');
+    });
+  });
+
+  describe('absolute path rejected', () => {
+    it.each([
+      '/etc/passwd',
+      '/root/.ssh/id_rsa',
+      sep + 'absolute',
+    ])('throws for %j', (input) => {
+      expect(() => fullPath(input)).toThrow('Invalid file path');
+    });
+  });
+
+  describe('prefix-confusion rejected', () => {
+    it('rejects a sibling directory whose name starts with the storage root', () => {
+      const siblingDriver = new LocalDriver({ storagePath: '/data/storage' });
+      const siblingFullPath = ((siblingDriver as any)._fullPath as FullPath).bind(siblingDriver);
+      // Attempt to reach /data/storage-evil/secret by traversal:
+      // resolve('/data/storage', '../storage-evil/secret') === '/data/storage-evil/secret'
+      // Without the `+ sep` guard, a startsWith check would match.
+      expect(() => siblingFullPath('../storage-evil/secret')).toThrow('Invalid file path');
+    });
+  });
+
+  describe('storage root itself', () => {
+    it('accepts the root when input resolves to it', () => {
+      expect(fullPath('')).toBe(ROOT);
+      expect(fullPath('.')).toBe(ROOT);
+      expect(fullPath('a/..')).toBe(ROOT);
+    });
+  });
+});
diff --git a/apps/server/src/integrations/storage/drivers/local.driver.ts b/apps/server/src/integrations/storage/drivers/local.driver.ts
index 39342c61..60be7c5d 100644
--- a/apps/server/src/integrations/storage/drivers/local.driver.ts
+++ b/apps/server/src/integrations/storage/drivers/local.driver.ts
@@ -3,7 +3,7 @@ import {
   LocalStorageConfig,
   StorageOption,
 } from '../interfaces';
-import { join, dirname } from 'path';
+import { dirname, resolve, sep } from 'path';
 import * as fs from 'fs-extra';
 import { Readable } from 'stream';
 import { createReadStream, createWriteStream } from 'node:fs';
@@ -17,7 +17,12 @@ export class LocalDriver implements StorageDriver {
   }
 
   private _fullPath(filePath: string): string {
-    return join(this.config.storagePath, filePath);
+    const storageRoot = resolve(this.config.storagePath);
+    const fullPath = resolve(storageRoot, filePath);
+    if (fullPath !== storageRoot && !fullPath.startsWith(storageRoot + sep)) {
+      throw new Error('Invalid file path');
+    }
+    return fullPath;
   }
 
   async upload(filePath: string, file: Buffer | Readable): Promise<void> {