diff --git a/src/schemas/shared.ts b/src/schemas/shared.ts
index c59e8e2..d2e2db4 100644
--- a/src/schemas/shared.ts
+++ b/src/schemas/shared.ts
@@ -1,3 +1,4 @@
+import path from 'node:path';
 import { z } from 'zod';
 
 export const ZoneNameSchema = z
@@ -16,7 +17,12 @@ export const ZoneNameSchema = z
         message: 'zone name cannot end with an underscore',
     });
 
+// Reduce to the final path segment before stripping reserved characters so
+// path-traversal sequences (../, absolute paths, alt-separators) cannot escape
+// the working directory once getAbsAndEnsureDir → path.resolve runs downstream.
+// path.basename only splits on the platform's native separator, so the regex
+// must still strip backslashes for POSIX hosts receiving Windows-shaped input.
 export const FilenameSchema = z
     .string()
     .min(1)
-    .transform((v) => v.replace(/[<>:"\\|?*]/g, '_'));
+    .transform((v) => path.basename(v).replace(/[<>:"\\|?*]/g, '_'));
diff --git a/tests/files.test.ts b/tests/files.test.ts
new file mode 100644
index 0000000..40022ea
--- /dev/null
+++ b/tests/files.test.ts
@@ -0,0 +1,136 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import path from 'node:path';
+import fs from 'node:fs/promises';
+import os from 'node:os';
+import { assertSchema } from '../src/schemas/utils';
+import { FilenameSchema } from '../src/schemas/shared';
+import { ValidationError } from '../src/utils/errors';
+import { bdclient } from '../src/client';
+
+describe('FilenameSchema — path traversal protection (CWE-22)', () => {
+    it('strips parent-directory traversal sequences', () => {
+        expect(assertSchema(FilenameSchema, '../../../etc/passwd')).toBe('passwd');
+        expect(assertSchema(FilenameSchema, '../etc/passwd')).toBe('passwd');
+        expect(
+            assertSchema(
+                FilenameSchema,
+                '../../../../../../../../../../tmp/pwned.txt',
+            ),
+        ).toBe('pwned.txt');
+    });
+
+    it('reduces POSIX absolute paths to the basename', () => {
+        expect(assertSchema(FilenameSchema, '/tmp/pwned.txt')).toBe('pwned.txt');
+        expect(assertSchema(FilenameSchema, '/etc/passwd')).toBe('passwd');
+        expect(assertSchema(FilenameSchema, '/a/b/c/d/e/f.json')).toBe('f.json');
+    });
+
+    it('reduces nested relative paths to the basename', () => {
+        expect(assertSchema(FilenameSchema, 'output/data.json')).toBe('data.json');
+        expect(assertSchema(FilenameSchema, 'a/b/c/file.txt')).toBe('file.txt');
+    });
+
+    it('strips Windows-style separators on POSIX hosts (regex fallback)', () => {
+        // path.basename on POSIX does not split on '\\', so the regex must.
+        const result = assertSchema(
+            FilenameSchema,
+            '..\\..\\Windows\\System32\\drivers\\etc\\hosts',
+        );
+        expect(result).not.toContain('\\');
+        expect(result).not.toContain('/');
+    });
+
+    it('preserves legitimate basenames untouched', () => {
+        expect(assertSchema(FilenameSchema, 'output.json')).toBe('output.json');
+        expect(assertSchema(FilenameSchema, 'my-data_2026.txt')).toBe(
+            'my-data_2026.txt',
+        );
+        expect(assertSchema(FilenameSchema, 'snapshot.csv')).toBe('snapshot.csv');
+    });
+
+    it('still strips Windows-reserved characters', () => {
+        expect(assertSchema(FilenameSchema, 'a<b>c:d"e|f?g*h.txt')).toBe(
+            'a_b_c_d_e_f_g_h.txt',
+        );
+    });
+
+    it('rejects empty input', () => {
+        expect(() => assertSchema(FilenameSchema, '')).toThrow(ValidationError);
+    });
+});
+
+describe('saveResults — path traversal protection', () => {
+    let client: bdclient;
+    let originalCwd: string;
+    let tmpDir: string;
+
+    beforeEach(async () => {
+        originalCwd = process.cwd();
+        // realpath: on macOS, os.tmpdir() returns /var/folders/... but
+        // path.resolve sees through the /private/var symlink, so canonicalize
+        // here so equality checks against resolved paths work cross-platform.
+        tmpDir = await fs.realpath(
+            await fs.mkdtemp(path.join(os.tmpdir(), 'brd-sdk-test-')),
+        );
+        process.chdir(tmpDir);
+        client = new bdclient({ apiKey: 'test-key-1234567890' });
+    });
+
+    afterEach(async () => {
+        await client.close();
+        process.chdir(originalCwd);
+        await fs.rm(tmpDir, { recursive: true, force: true });
+    });
+
+    it('keeps a ../../../tmp/<file> payload inside the working directory', async () => {
+        const sentinel = `brd-pwn-test-${Date.now()}.txt`;
+        const malicious = `../../../../../../../../../../tmp/${sentinel}`;
+        const escapeTarget = path.join('/tmp', sentinel);
+
+        // Ensure no pre-existing sentinel from a previous run.
+        await fs.unlink(escapeTarget).catch(() => {});
+
+        const saved = await client.saveResults('payload', {
+            filename: malicious,
+            format: 'txt',
+        });
+
+        // The escape target must not have been created.
+        await expect(fs.stat(escapeTarget)).rejects.toThrow();
+
+        // The actual write landed inside our isolated tmpDir.
+        expect(saved.startsWith(tmpDir + path.sep)).toBe(true);
+        expect(path.basename(saved)).toBe(sentinel);
+
+        const content = await fs.readFile(saved, 'utf8');
+        expect(content).toBe('payload');
+    });
+
+    it('reduces absolute /tmp paths to a basename in the working directory', async () => {
+        const sentinel = `absolute-pwn-${Date.now()}.txt`;
+        const malicious = `/tmp/${sentinel}`;
+        const escapeTarget = `/tmp/${sentinel}`;
+
+        await fs.unlink(escapeTarget).catch(() => {});
+
+        const saved = await client.saveResults('payload', {
+            filename: malicious,
+            format: 'txt',
+        });
+
+        await expect(fs.stat(escapeTarget)).rejects.toThrow();
+        expect(saved.startsWith(tmpDir + path.sep)).toBe(true);
+        expect(path.basename(saved)).toBe(sentinel);
+    });
+
+    it('writes legitimate basenames at the expected location', async () => {
+        const name = `output-${Date.now()}.txt`;
+        const saved = await client.saveResults('hello', {
+            filename: name,
+            format: 'txt',
+        });
+
+        expect(saved).toBe(path.join(tmpDir, name));
+        expect(await fs.readFile(saved, 'utf8')).toBe('hello');
+    });
+});