网络扫描技术揭秘读书笔记3--TCP SYN扫描

TCP SYN扫描（使用Winpcap库实现）

0.核心原理

半开扫描（TCP SYN）不同于CSocket和Socket2扫描，后两者扫描都是完成了一个完整的三次握手（即connect函数），而半开扫描则只完成了两次握手就宣告结果，因为仅通过两次握手已读到了要读的数据。

扫描函数的原理就是完成三次握手中的前两次，其中第一次是由扫描器向被扫描的服务器端发送SYN同步数据包，第二次是服务器端回复扫描器ACK确认数据包。按原“计划”，扫描器应该再向服务器发送一个ACK确认包完成三次握手，然而TCP SYN半开扫描在第三次握手时中止该操作或者向服务器端发送FIN结束数据包。

1.使用核心库函数以及核心代码：

#include <pcap.h>#include <iphlpapi.h>#pragma comment(lib,"iphlpapi.lib")#define DEF_BUF_SIZE 100#define ACK_SYN 1#define ACK_RST 0#define ILLEGAL_FLAG -1#define MAX_FRAME_LEN 1500//IP地址转换处理typedef union MultiByteStruct  {//IP地址联合体      int iInt;   //int有符号整型      float fFloat;   //浮点数      UINT uInt;  //无符号整数      ULONG uLong;    //ULONG无符号整型      DWORD dwDword;  //DWORD有符号整型      WORD wWord[2];  //WORD无符号整型数组      UCHAR ucByte[4];    //无符号字符数组      char cByte[4];  //字符数组  }UNIONIP,*PUNIONIP; SYNTHREADPARAM SynThreadParam;//传递给TCP SYNSCAN 线程的参数结构体static USHORT g_uLocalPort=1240;//绑定的本地端口号USHORT CPortScan_TCPDlg::CheckSum(USHORT *buffer, int size){unsigned long cksum=0;      while(size>1)      {          cksum+=*buffer++;          size-=sizeof(USHORT);      }      if(size)      {          cksum+=*(UCHAR*)buffer;      }      cksum=(cksum>>16)+(cksum&0xffff);      cksum+=(cksum>>16);      return (USHORT)(~cksum);  }CString IPIntToStr(UINT IPInt){CString IPStr;  UNIONIP IP;  IP.uInt=IPInt;  //IPStr.Format(_T("%d.%d.%d.%d"),IP.ucByte[0],IP.ucByte[1],IP.ucByte[2],IP.ucByte[3]);IPStr.Format(_T("%d.%d.%d.%d"),IP.ucByte[3],IP.ucByte[2],IP.ucByte[1],IP.ucByte[0]);return IPStr;    }//char *->CStringvoid CharStrToCString(CString *str,const char *char_str)  {int byteLen=strlen(char_str); int Charlen=MultiByteToWideChar(CP_ACP,0,char_str,byteLen,NULL,0);  TCHAR *TcharTempItem=new TCHAR[Charlen+1];    MultiByteToWideChar(CP_ACP,0,char_str,byteLen,TcharTempItem,Charlen);  TcharTempItem[Charlen]='\0';*str=TcharTempItem;//*****}void  CPortScan_TCPDlg::SynScan_By_WinpCap(UNIONIP uIPBegin,UNIONIP uIPEnd,UINT uPortBegin,UINT uPortEnd){MessageBox(_T("sys scan by winpcap style..."));PSDHEADER psdHeader;    //伪TCP包头  UCHAR *tcp_packet_str=new UCHAR[MIN_TCPPACKET_LEN+1];PACKET tcp_packet;UINT SrcIp;// 获取本地地址信息char szLocalName[DEF_BUF_SIZE]={0};gethostname(szLocalName,DEF_BUF_SIZE);hostent* pHost=gethostbyname(szLocalName);if(pHost!=NULL)memcpy(&SrcIp,pHost->h_addr_list[0],pHost->h_length);elsereturn ;//获取网卡设备句柄pcap_t *fp;pcap_if_t *d;GetAdapterHandle(&fp,&d);if(!fp)MessageBox(_T("获取网卡设备句柄失败！"));//recv response packet (ACK+SYN)//Theread:监听目标主机（UNIONIP uIPBegin,UNIONIP uIPEnd）的TCP响应数据包SynThreadParam.fp=fp;SynThreadParam.d=d;SynThreadParam.uIPBegin=uIPBegin;SynThreadParam.uIPEnd=uIPEnd;SynThreadParam.SrcIp=SrcIp;SynThreadParam.ptr=this;CString strIP=IPIntToStr(uIPBegin.uInt);HTREEITEM curr=m_ctlTreeResult.InsertItem(strIP,1,1,TVI_ROOT); SynThreadParam.TreeItem=curr;AfxBeginThread(ThreadRecvTCPSYNPacket,&SynThreadParam,THREAD_PRIORITY_IDLE);//监听返回的ACK+SYN数据包Sleep(1000);//预留做监听的准备时间   或者设置定时器判断  开始发送数据包的时间 12.16//end for 12.16for (UINT ip=uIPBegin.uInt;ip<=uIPEnd.uInt;ip++)  {BYTE SrcMac[6];BYTE DstMac[6];GetMacAddress(SrcMac);//GetMacAddrOfIP(ip,DstMac);//for(UINT port=m_uPortBegin;port<=m_uPortEnd;port++)  { memset(tcp_packet_str,0,MIN_TCPPACKET_LEN+1);memset(&tcp_packet,0,sizeof(PACKET));//EtherHeader partmemcpy(tcp_packet.ethhead.DestMac,DstMac,6);memcpy(tcp_packet.ethhead.SrcMac,SrcMac,6);USHORT type=0x0800;//***以太网帧类型   0x0800  网际协议  ***tcp_packet.ethhead.Type=htons(type);//分别自己填充IP头、TCP头、伪TCP头，并计算其中的校验和  //设置IP头   tcp_packet.ipHeader.h_verlen=0x45;   tcp_packet.ipHeader.tos=0;   tcp_packet.ipHeader.total_len=htons(sizeof(IPHEADER)+sizeof(TCPHEADER));   tcp_packet.ipHeader.ident=1;   tcp_packet.ipHeader.frag_and_flags=0;   tcp_packet.ipHeader.ttl=128;   tcp_packet.ipHeader.proto=IPPROTO_TCP;   tcp_packet.ipHeader.checksum=0;   tcp_packet.ipHeader.sourceIP=SrcIp;   tcp_packet.ipHeader.destIP=htonl(ip);//   //设置TCP头   tcp_packet.translayer.tcpHeader.th_sport=htons(g_uLocalPort);   tcp_packet.translayer.tcpHeader.th_dport=htons(port); //tcp_packet.translayer.tcpHeader.th_seq=htonl(SEQ);  tcp_packet.translayer.tcpHeader.th_ack=0;   tcp_packet.translayer.tcpHeader.th_lenres=(sizeof(TCPHEADER)/4<<4|0);   tcp_packet.translayer.tcpHeader.th_flag=2; //2：SYN；1：FIN；16：ACK   tcp_packet.translayer.tcpHeader.th_win=htons(512);   tcp_packet.translayer.tcpHeader.th_urp=0;   tcp_packet.translayer.tcpHeader.th_sum=0;  //伪TCP头  psdHeader.saddr=tcp_packet.ipHeader.sourceIP;psdHeader.daddr=tcp_packet.ipHeader.destIP;   psdHeader.mbz=0;   psdHeader.ptcl=IPPROTO_TCP;   psdHeader.tcpl=htons(sizeof(TCPHEADER));   //TCP头校验和  checksum(PsdHeader+TcpHeader)char tempBuf[40];memcpy(tempBuf,&psdHeader,sizeof(PSDHEADER));memcpy(tempBuf+sizeof(psdHeader),&tcp_packet.translayer.tcpHeader,sizeof(TCPHEADER));tcp_packet.translayer.tcpHeader.th_sum=CheckSum((USHORT*)tempBuf,sizeof(PSDHEADER)+sizeof(TCPHEADER));//*****IP头校验和   checksum(IpHeader)memcpy(tempBuf,&tcp_packet.ipHeader,sizeof(IPHEADER));tcp_packet.ipHeader.checksum=CheckSum((USHORT*)tempBuf,sizeof(IPHEADER));//数据包流序列化memcpy(tcp_packet_str,(UCHAR*)&tcp_packet,sizeof(PACKET));SetDlgItemInt(IDC_PORT_EDIT,port);if(pcap_sendpacket(fp,tcp_packet_str,sizeof(PACKET)) != 0)//发送数据包  sizeof(PACKET){MessageBox(_T("pcap_sendpacket()函数执行发生错误！"));return;}}}}//[in] Param :{fp,d,IP,ptr,TreeItem...}UINT ThreadRecvTCPSYNPacket(LPVOID pParam){//capture,resolve,check  12.16SYNTHREADPARAM *SynThreadParam=(SYNTHREADPARAM *)pParam;pcap_t *fp=SynThreadParam->fp;pcap_if_t *d=SynThreadParam->d;UNIONIP uIPBegin=SynThreadParam->uIPBegin;UNIONIP uIPEnd=SynThreadParam->uIPEnd;UINT SrcIp=SynThreadParam->SrcIp;CPortScan_TCPDlg *ptr=SynThreadParam->ptr;     HTREEITEM curr=SynThreadParam->TreeItem; const BYTE *pkt_data=new BYTE[MAX_FRAME_LEN];UINT res;struct pcap_pkthdr *header;char *packet_filter_str=new char[100];char SrcIp_str[16],DstIp_str[16];SOCKADDR_IN addr_src,addr_dst;struct bpf_program fcode;bpf_u_int32 NetMask;if(d->addresses->netmask)NetMask=((struct sockaddr_in *)d->addresses->netmask)->sin_addr.s_addr;elseNetMask=0xffffff;//filter response tcp packets//tcp and ip src host (uIPBegin to uIPEnd)  and ip dst host localhost//for (UINT ip=uIPBegin.uInt;ip<=uIPEnd.uInt;ip++)memset(packet_filter_str,0,100);strcpy(packet_filter_str,"tcp and ip src host ");addr_dst.sin_addr.S_un.S_addr=htonl(uIPBegin.uInt);//***only the first destination host(12.16)strcpy(SrcIp_str,inet_ntoa(addr_dst.sin_addr));//SrcIpstrcat(packet_filter_str,SrcIp_str);strcat(packet_filter_str," and ip dst host ");addr_src.sin_addr.S_un.S_addr=SrcIp;strcpy(DstIp_str,inet_ntoa(addr_src.sin_addr));//DstIpstrcat(packet_filter_str,DstIp_str);if(pcap_compile(fp, &fcode, packet_filter_str, 1, NetMask)<0){AfxMessageBox(_T("Error compiling filter: wrong syntax."));return 1;}if(pcap_setfilter(fp, &fcode)<0){AfxMessageBox(_T("Error setting the filter."));return 1;}int elapse_times=0;while((res=pcap_next_ex(fp,&header,&pkt_data))>=0){if(elapse_times>10)//根据超时次数粗略确定已经没有余下的响应数据包break;if(res==0){//ptr->MessageBox(_T("获取报文超时!"));elapse_times++;continue;}//resolve received tcp_packet and check relevant bitsPACKET *TcpPacket=(PACKET *)pkt_data;int iphead_len=((TcpPacket->ipHeader.h_verlen)&0x0f)*4;TCPHEADER *TcpHeader=(TCPHEADER *)(pkt_data+sizeof(ETHERNET_HEAD)+iphead_len);UCHAR flag=TcpHeader->th_flag;USHORT opened_port=ntohs(TcpHeader->th_sport);//ntohs()  12.16 p.m.CString strTemp;if(((flag&0x10)>>4)&((flag&0x02)>>1))//0 0 URG ACK PSH RST SYN FIN{struct servent *se;  CString strNameTemp;se=getservbyport(TcpHeader->th_sport,"tcp");  if(se!=NULL)  //get the info of the port and corresponding server name{strTemp.Format(_T("%d "),opened_port);CharStrToCString(&strNameTemp,se->s_name);strTemp+=strNameTemp;}else  strTemp.Format(_T("%d"),opened_port);  ptr->m_ctlTreeResult.InsertItem(strTemp,2,2,curr); //insert the port node into the tree}}if(res == -1){AfxMessageBox(_T("Error reading the packets"));return 1;}ptr->MessageBox(_T("Finished SynScan..."));return 1;}void GetMacAddress(BYTE *mac_addr){IP_ADAPTER_INFO adapter[5];  //Maximum 5 adaptersDWORD buflen=sizeof(adapter);DWORD status=GetAdaptersInfo(adapter,&buflen);BYTE s[8];if(status==ERROR_SUCCESS){PIP_ADAPTER_INFO painfo=adapter;memcpy(s,painfo->Address,6);for(int i=0;i<6;i++){mac_addr[i]=s[i];}}}void GetAdapterHandle(pcap_t **fp,pcap_if_t **d){pcap_if_t *alldevs;char errbuf[PCAP_ERRBUF_SIZE];int i,inum;//网卡设备编号if(pcap_findalldevs(&alldevs, errbuf) == -1){AfxMessageBox(_T("pcap_findalldevs()函数执行发生错误！"));exit(1);}inum=3;//如何动态获取本地连接网卡  --需改进for (*d=alldevs, i=0; i< inum-1 ;*d=(*d)->next, i++);if ((*fp = pcap_open_live((*d)->name,65536,1,1000,errbuf)) == NULL){AfxMessageBox(_T("打开适配器发生错误"));exit(1);}}void GetMacAddrOfIP(UINT ip,BYTE *mac_addr){//获取网卡设备句柄pcap_t *fp;pcap_if_t *d;GetAdapterHandle(&fp,&d);if(!fp)AfxMessageBox(_T("获取网卡设备句柄失败！"));// 获取本地地址信息：IP和MACUINT SrcIP;UINT DstIP=ip;//[in] formal parameterBYTE SrcMac[6];BYTE DstMac[6];char szLocalName[DEF_BUF_SIZE]={0};gethostname(szLocalName,DEF_BUF_SIZE);hostent* pHost=gethostbyname(szLocalName);if(pHost!=NULL)memcpy(&SrcIP,pHost->h_addr_list[0],pHost->h_length);elsereturn ;GetMacAddress(SrcMac);memset(DstMac,0xff,6);//1.构造ARP请求包//SrcMac SrcIP  DstMac DstIP=ipARP_PACKET arp_request;USHORT type=0x0806;USHORT hardware_type=0x0001;USHORT protocol_type=0x0800;BYTE mac_len=0x06;BYTE ip_len=0x04;USHORT option=0x0001;//1  Request//MAC Frame Headmemset(&arp_request,0,sizeof(ARP_PACKET));memcpy(arp_request.EthHead.DestMac,DstMac,6);memcpy(arp_request.EthHead.SrcMac,SrcMac,6);arp_request.EthHead.Type=htons(type);//ARP Request Headarp_request.ArpFrame.hardware_type=htons(hardware_type);arp_request.ArpFrame.protocol_type=htons(protocol_type);arp_request.ArpFrame.add_len=mac_len;arp_request.ArpFrame.pro_len=ip_len;arp_request.ArpFrame.option=htons(option);memcpy(arp_request.ArpFrame.sour_addr,SrcMac,6);arp_request.ArpFrame.sour_ip=SrcIP;//SrcIP: net sequencememcpy(arp_request.ArpFrame.dest_addr,DstMac,6);arp_request.ArpFrame.dest_ip=htonl(DstIP);//DstIP UINT:host sequence memset(arp_request.ArpFrame.padding,0x00,18);if(pcap_sendpacket(fp,(BYTE *)&arp_request,sizeof(arp_request)) != 0){AfxMessageBox(_T("pcap_sendpacket()函数执行发生错误！"));return;}//2.recv arp response packetconst BYTE *pkt_data;UINT res;struct pcap_pkthdr *header;char *packet_filter_str=new char[100];char mac_str[18];char ip_str[16];struct bpf_program fcode;bpf_u_int32 NetMask;if(d->addresses->netmask)//掩码不为空NetMask=((struct sockaddr_in *)d->addresses->netmask)->sin_addr.s_addr;elseNetMask=0xffffff;//默认为 C类网络GetMacStrFromByte(SrcMac,mac_str);//MAC StrSOCKADDR_IN addr;addr.sin_addr.S_un.S_addr=htonl(DstIP);//************下面的innet_ntoa()参数是--网络上--的一个IP地址************strcpy(ip_str,inet_ntoa(addr.sin_addr));//IP Str//packet_filter_str="arp and ether dst str(SrcMac) and src host str(DstIP)"//packet_filter_str   +=  arp_request.ArpFrame.option=0x0002memset(packet_filter_str,0,100);strcpy(packet_filter_str,"arp and ether dst ");strcat(packet_filter_str,mac_str);strcat(packet_filter_str," and src host ");strcat(packet_filter_str,ip_str);if(pcap_compile(fp, &fcode, packet_filter_str, 1, NetMask)<0){AfxMessageBox(_T("Error compiling filter: wrong syntax."));return;}if(pcap_setfilter(fp, &fcode)<0){AfxMessageBox(_T("Error setting the filter."));return ;}/* Capture data */while((res = pcap_next_ex(fp,&header,&pkt_data))>=0){if(res == 0)/* Timeout elapsed */continue;if(pkt_data)break;}if(res == -1){AfxMessageBox(_T("Error reading the packets"));return;}//3.resolve response arp arp packet of sour_addr attribute//const BYTE * pkt_data  -->SrcMacETHERNET_HEAD *Ether_Header=(ETHERNET_HEAD *)pkt_data;memcpy(mac_addr,Ether_Header->SrcMac,6);}void GetMacStrFromByte(BYTE *SrcMac,char *mac_str){/*In:  SrcMac={00,30,18,A3,D2,8E};Out: mac_str="00:30:18:A3:D2:8E"*/char *MacStr=new char[18];memset(MacStr,0,18);for(int i=0;i<6;i++){MacStr[3*i]=GetHexChar((SrcMac[i]&0xf0)>>4);MacStr[3*i+1]=GetHexChar(SrcMac[i]&0x0f);if(i<=4)MacStr[3*i+2]=':';}strcpy(mac_str,MacStr);}char GetHexChar(BYTE HexNum){if(HexNum>=0&&HexNum<=9)return '0'+HexNum;else if(HexNum>=0xA&&HexNum<=0xF)return 'A'+HexNum-0xA;else{AfxMessageBox(_T("Illegal HexNum!"));return 0;}}

2.运行结果分析：

（1）

TCP SYN扫描结果：发现目标主机出现超时重ACK+SYN 数据包的现象

第一个重传(TCP Retransmission)的数据包是来自目标主机的端口netbios-ssn(139)的数据包

使用Wireshark工具得到该数据包的SEQ/ACK分析：判断为可疑的重传数据包

（2）

添加端口对应的服务名称之后，最终的运行结果：

（3）使用nmap扫描工具进行对比：

3.忽略掉的问题

只扫描了知名端口（1-1024）；

没有动态识别本地连接对应的网卡；

没有对重传数据包的判定；

只考虑了对单一主机的扫描，没有考虑多个目标主机的情况；

获取的端口服务名只是使用getservbyport()从本地配置文件读取；

接收TCP响应包的线程函数的退出仅仅根据超时次数，没有恰当处理退出的条件；

其它

......

4.定义的相关数据结构

#pragma pack (1)typedef struct SYNThreadParamStruct{pcap_t *fp;pcap_if_t *d;UNIONIP uIPBegin;UNIONIP uIPEnd;UINT SrcIp;CPortScan_TCPDlg *ptr;     HTREEITEM TreeItem; }SYNTHREADPARAM;//以太网帧头typedef struct _ETHERNET_HEAD{BYTE DestMac[6];//目的MAC地址BYTE SrcMac[6];//源MAC地址USHORT Type;//协议类型 IP(0x0800) ARP(0x0806是ARP帧的类型值)  RARP}ETHERNET_HEAD;//14Bytestypedef struct _ARP_HEADER{ //固定头长度：28BytesUSHORT hardware_type; //硬件类型：以太网接口类型为1 USHORT protocol_type; //协议类型：IP协议类型为0X0800 BYTE add_len; //硬件地址长度：MAC地址长度为6B BYTE pro_len; //协议地址长度：IP地址长度为4B USHORT option; //操作：ARP请求为1，ARP应答为2 BYTE sour_addr[6]; //源MAC地址：发送方的MAC地址 UINT sour_ip; //源IP地址：发送方的IP地址 BYTE dest_addr[6]; //目的MAC地址：ARP请求中该字段没有意义；ARP响应中为接收方的MAC地址 UINT dest_ip; //目的IP地址：ARP请求中为请求解析的IP地址；ARP响应中为接收方的IP地址BYTE padding[18]; //填充字符长度=以太网最小帧长(64Bytes)-MAC帧头(14Bytes)-ARP包固定长度(28Bytes)-帧校验序列FCS(4Bytes)}ARP_HEADER,*PARP_HEADER; // ARP Packet = ETHERNET_HEAD + ARP_HEADERtypedef struct _ARP_PACKET{ETHERNET_HEAD EthHead;ARP_HEADER ArpFrame;}ARP_PACKET,*PARP_PACKET;typedef struct _iphdr  {      unsigned char h_verlen;     //4位IP版本号+4位首部长度    unsigned char tos;  //8位服务类型TOS      unsigned short total_len;   //16位总长度（字节）      unsigned short ident;   //16位标识  标记当前分片为第几个分片    unsigned short frag_and_flags;  //3位标志位+13位片偏移    unsigned char ttl;  //8位生存时间 TTL      unsigned char proto;    //8位协议(TCP、UDP或其他协议)      unsigned short checksum;    //16位IP首部校验和      unsigned int sourceIP;  //32位源IP地址      unsigned int destIP;    //32位目的IP地址  }IPHEADER;  //TCP伪首部的作用主要是进行校验和的计算  typedef struct psd_hdr  //定义TCP伪首部   12Bytes{       unsigned long saddr;    //源地址       unsigned long daddr;    //目的地址       char mbz;       char ptcl;  //协议类型       unsigned short tcpl;    //TCP长度   }PSDHEADER;   typedef struct _tcphdr  //定义TCP首部  {      USHORT th_sport;    //16位源端口      USHORT th_dport;    //16位目的端口      unsigned int th_seq;    //32位序列号      unsigned int th_ack;    //32位确认号     unsigned char th_lenres;    //4位首部长度/6位保留字      unsigned char th_flag;  //6位标志位     USHORT th_win;  //16位窗口大小      USHORT th_sum;  //16位校验和      USHORT th_urp;  //16位紧急数据偏移量  }TCPHEADER;    //数据包typedef struct _packet  {  ETHERNET_HEAD  ethhead;    IPHEADER ipHeader;      union Translayer      {  TCPHEADER tcpHeader;          UDPHEADER udpHeader;          ICMPHEADER icmpHeader;      }translayer;  //char padding[10];//填充字符}PACKET;  #pragma pack()