diff --git a/.changeset/safe-download-filenames.md b/.changeset/safe-download-filenames.md
new file mode 100644
index 0000000000..6b8812bf46
--- /dev/null
+++ b/.changeset/safe-download-filenames.md
@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kimi-code": patch
+---
+
+Sanitize filenames in session file download response headers.
diff --git a/packages/kap-server/src/routes/fs.ts b/packages/kap-server/src/routes/fs.ts
index 598da6d85a..d21bc5e5d4 100644
--- a/packages/kap-server/src/routes/fs.ts
+++ b/packages/kap-server/src/routes/fs.ts
@@ -963,8 +963,9 @@ function buildValidationEnvelope(
   };
 }
 
-function sanitizeFilename(rel: string): string {
+export function sanitizeFilename(rel: string): string {
   const segs = rel.split('/');
-  const base = segs[segs.length - 1] ?? rel;
-  return base.replace(/"/g, '\\"');
+  const base = segs.at(-1) ?? rel;
+  const sanitized = base.replaceAll(/[\u0000-\u001F\u007F"\\]/g, '_');
+  return sanitized.length > 0 ? sanitized : 'download';
 }
diff --git a/packages/kap-server/test/fs.test.ts b/packages/kap-server/test/fs.test.ts
index de43d11250..526f915a02 100644
--- a/packages/kap-server/test/fs.test.ts
+++ b/packages/kap-server/test/fs.test.ts
@@ -8,6 +8,7 @@ import { FakeRuntime } from '@moonshot-ai/agent-core-v2/runtime/fakeRuntime';
 import { ErrorCode } from '../src/protocol/error-codes';
 import { afterAll, afterEach, beforeAll, beforeEach, describe, expect, it } from 'vitest';
 
+import { sanitizeFilename } from '../src/routes/fs';
 import { type RunningServer, startServer } from '../src/start';
 import { TEST_HOST_IDENTITY } from './helpers/hostIdentity';
 import { authHeaders } from './helpers/auth';
@@ -354,6 +355,10 @@ describe('server-v2 /api/v1 fs routes', () => {
     }
   });
 
+  it('sanitizeFilename strips control characters and path separators', async () => {
+    expect(sanitizeFilename('bad"name\\.txt')).toBe('bad_name_.txt');
+  });
+
   async function postWorkspaceSearch<T>(body: unknown): Promise<Envelope<T>> {
     const res = await fetch(`${base}/api/v1/workspace/fs:search`, {
       method: 'POST',