diff --git a/lib/HttpClient.php b/lib/HttpClient.php
index 5d7a4823..deb1868d 100644
--- a/lib/HttpClient.php
+++ b/lib/HttpClient.php
@@ -236,11 +236,58 @@ private function resolveUrl(string $path, ?RequestOptions $options): string
             return $path;
         }
 
+        $this->assertSafePath($path);
+
         $baseUrl = $options !== null && $options->baseUrl !== null ? $options->baseUrl : $this->baseUrl;
         $baseUrl = rtrim($baseUrl, '/');
         return $baseUrl . '/' . ltrim($path, '/');
     }
 
+    /**
+     * Reject paths whose segments could escape the intended endpoint once
+     * normalized by the HTTP transport or the receiving server. Service
+     * methods interpolate caller-supplied IDs into path templates without
+     * per-segment URL-encoding, so an unencoded "../" or embedded "?"/"#"/CRLF
+     * in a single ID would silently re-target the request at a different
+     * WorkOS resource under the application's authenticated API key.
+     *
+     * The check runs against the fully percent-decoded path so that encoded
+     * variants (`%2e%2e`, `%2f`, `%3f`, `%0d%0a`, ...) and double-encoded
+     * variants (`%252e%252e`, `%252f`, ...) cannot bypass it.
+     */
+    private function assertSafePath(string $path): void
+    {
+        $decoded = self::decodeUntilStable($path);
+
+        if (preg_match('/[\x00-\x1f?#]/', $decoded) === 1) {
+            throw new \InvalidArgumentException(
+                'WorkOS request path contains a forbidden character (control character, "?", or "#"). Pass query parameters via the $query argument rather than embedding them in the path.',
+            );
+        }
+
+        foreach (explode('/', $decoded) as $segment) {
+            if ($segment === '.' || $segment === '..') {
+                throw new \InvalidArgumentException(
+                    'WorkOS request path contains a relative segment ("." or ".."). Refusing to send the request to avoid cross-resource redirection.',
+                );
+            }
+        }
+    }
+
+    /**
+     * Decode percent-encoded characters in a loop until the value stabilizes,
+     * closing double-encoding bypass vectors like `%252e%252e`.
+     */
+    private static function decodeUntilStable(string $value): string
+    {
+        do {
+            $prev = $value;
+            $value = rawurldecode($value);
+        } while ($value !== $prev);
+
+        return $value;
+    }
+
     private function resolveTimeout(?RequestOptions $options): int
     {
         return $options !== null && $options->timeout !== null ? $options->timeout : $this->timeout;
diff --git a/tests/HttpClientTest.php b/tests/HttpClientTest.php
index 34af98a6..429c5ec4 100644
--- a/tests/HttpClientTest.php
+++ b/tests/HttpClientTest.php
@@ -85,6 +85,88 @@ public function testBuildUrlAppendsQueryString(): void
         $this->assertSame('code', $query['response_type']);
     }
 
+    /**
+     * @return array<string, array{0: string}>
+     */
+    public static function unsafePathProvider(): array
+    {
+        return [
+            'parent traversal segment' => ['connections/../webhook_endpoints/wh_target'],
+            'leading parent traversal' => ['../webhook_endpoints/wh_target'],
+            'current directory segment' => ['connections/./id'],
+            'embedded query character' => ['connections/conn_123?override=1'],
+            'embedded fragment character' => ['connections/conn_123#frag'],
+            'embedded carriage return' => ["connections/conn_123\r\nHost: evil"],
+            'embedded newline' => ["connections/conn_123\nfoo"],
+            'embedded null byte' => ["connections/conn_123\x00"],
+            'percent-encoded parent traversal lowercase' => ['connections/%2e%2e/webhook_endpoints/wh_target'],
+            'percent-encoded parent traversal uppercase' => ['connections/%2E%2E/webhook_endpoints/wh_target'],
+            'percent-encoded current directory segment' => ['connections/%2e/id'],
+            'percent-encoded slash hides traversal' => ['connections%2F..%2Fwebhook_endpoints'],
+            'percent-encoded slash hides encoded traversal' => ['connections%2F%2e%2e%2Fwebhook_endpoints'],
+            'percent-encoded query character' => ['connections/conn_123%3Foverride=1'],
+            'percent-encoded fragment character' => ['connections/conn_123%23frag'],
+            'percent-encoded CRLF injection' => ['connections/conn_123%0D%0AHost:%20evil'],
+            'percent-encoded null byte' => ['connections/conn_123%00'],
+            'double-encoded parent traversal' => ['connections/%252e%252e/webhook_endpoints'],
+            'double-encoded slash hides traversal' => ['connections%252F..%252Fwebhook_endpoints'],
+            'double-encoded query character' => ['connections/conn_123%253Foverride=1'],
+            'double-encoded null byte' => ['connections/conn_123%2500'],
+        ];
+    }
+
+    /**
+     * @dataProvider unsafePathProvider
+     */
+    public function testRequestRejectsUnsafePaths(string $path): void
+    {
+        $client = new HttpClient(
+            apiKey: 'test_key',
+            clientId: null,
+            baseUrl: 'https://api.workos.com',
+            timeout: 10,
+            maxRetries: 0,
+        );
+
+        $this->expectException(\InvalidArgumentException::class);
+        $client->request('DELETE', $path);
+    }
+
+    /**
+     * @dataProvider unsafePathProvider
+     */
+    public function testBuildUrlRejectsUnsafePaths(string $path): void
+    {
+        $client = new HttpClient(
+            apiKey: 'test_key',
+            clientId: null,
+            baseUrl: 'https://api.workos.com',
+            timeout: 10,
+            maxRetries: 0,
+        );
+
+        $this->expectException(\InvalidArgumentException::class);
+        $client->buildUrl($path);
+    }
+
+    public function testRequestAllowsSafePathsWithDotsInsideSegments(): void
+    {
+        $mock = new MockHandler([
+            new Response(200, ['Content-Type' => 'application/json'], '{}'),
+        ]);
+
+        $client = new HttpClient(
+            apiKey: 'test_key',
+            clientId: null,
+            baseUrl: 'https://api.workos.com',
+            timeout: 10,
+            maxRetries: 0,
+            handler: HandlerStack::create($mock),
+        );
+
+        $this->assertSame([], $client->request('GET', 'users/user.with.dots'));
+    }
+
     public function testErrorResponseIncludesCodeAndError(): void
     {
         $body = json_encode([