技术文章 > 简捷实用的VB防黑手段

简捷实用的VB防黑手段

2017-12-12 04:42

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当我们担心被黑客攻击或怀疑电脑被植入木马时,我们往往求助于防火墙。其实,避免用宰牛刀的手段有很多,本文即通过实时监控全部 TCP连接的方法来实现防黑。
一、监控 TCP连接

黑客程序或木马程序的本质是实现数据传输。TCP和UDP(用户数据文报协议)是两个最常用的数据传输协议,它们都使用设置监听端口的方法来完成数据传输。

实时监控所有端口的连接情况、及时对异常连接发出警告并提示用户删除异常连接,就可以有效地达到防黑目的。
使用微软的IP助手库函数(iphlpapi.dll)是一个捷径。其中的 GetTcpTable函数能返回当前系统中全部有效的 TCP连接。其定义为:
DWORD GetTcpTable(
PMIB_TCPTABLE pTcpTable, // buffer for the connection table
PDWORD pdwSize, // size of the buffer
BOOL bOrder // sort the table?
);

其中参数一是 TCP连接表缓冲区的指针,参数二是缓冲区大小(当缓冲区不够大时,该参数返回实际需要的大小),参数三指示连接表是否需要按“Local IP”、“Localport”、“Remote IP”、“Remote port”依次进行排序。
对于监控 UDP连接表,可使用 GetUdpTable函数完成。由于在使用上完全类似,这里略去讨论(后面的实例程序中也相应地略去了对 UDP的监控)。
二、异常警告及删除连接

通过定时比较前后两个 TCP连接表,我们可以立即发现异常并发出警告。后面的实例程序用声音和报警标志提醒用户注意可能的外界入侵。
收到警告信号后,我们应首先将可疑连接删除掉,然后再仔细查找系统中是否有安全漏洞或有可疑进程在工作。IP助手库函数中的 SetTcpEntry函数可以帮助我们删除可疑连接。其定义为:
DWORD SetTcpEntry(
PMIB_TCPROW pTcpRow // pointer to struct. with new state info
);
在调用此函数之前,应将欲删连接的状态置为 MIB_TCP_STATE_DELETE_TCB(删除)。MIB_TCP_STATE_DELETE_TCB也是目前唯一可在运行时设置的状态。
三、实例程序及其运行情况

下面的三幅示意图分别展示了:(1) 系统被攻击前的状况,(2) 系统被目前流行的“冰河”远程攻击软件入侵后而发出警告的状况,以及(3) 用户正在清除可疑连接时的状况。



下面是实例程序的完整代码:
“ 黑客入侵监控程序(VB6)
Option Explicit
Private Type MIB_TCPROW “ TCP连接表中一行的结构
dwState As Long “ 状态
dwLocalAddr As Long “ Local IP
dwLocalPort As Long “ Local port
dwRemoteAddr As Long “ Remote IP
dwRemotePort As Long “ Remote port
End Type
Private Type MIB_TCPTABLE
dwNum_Of_Entries As Long “ 当前 TCP连接的总数
TCP_Table(120) As MIB_TCPROW “ 预留了120行的缓冲区
End Type
Private Declare Function GetTcpTable Lib "iphlpapi.dll" (ByRef pTcpTable _
As MIB_TCPTABLE, ByRef pdwSize As Long, ByVal bOrder As Long) As Long
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (ByRef _
pDest As Any, ByRef pSource As Any, ByVal Length As Long)
Private Declare Function sndPlaySound Lib "winmm.dll" Alias "sndPlaySoundA" _
(ByVal lpszSoundName As String, ByVal uFlags As Long) As Long
Private Declare Function GetWindowsDirectory Lib "kernel32" Alias _
"GetWindowsDirectoryA" (ByVal lpBuffer As String, ByVal nSize As Long) As Long
Private Declare Function SetTcpEntry Lib "iphlpapi.dll" (ByRef pTcpTable _
As MIB_TCPROW) As Long
Dim Last_Num_Of_Entries As Long
Dim TCP1 As MIB_TCPTABLE
Private Sub Form_Load()
Timer1.Interval = 10000 “ 定时监控
Timer1_Timer
End Sub
Private Sub Timer1_Timer()
Dim Return1 As Long, i As Long, Tmp1 As Long, Tmp2 As Long
Dim Ip_Buf(1 To 4) As Byte
Dim Win_Path As String, Tmp3 As String
Return1 = GetTcpTable(TCP1, Len(TCP1), 1) “ 返回 TCP连接表
If Last_Num_Of_Entries <> 0 And _
Last_Num_Of_Entries <> TCP1.dwNum_Of_Entries Then “ 有异常时发出警告
Picture1.Visible = True “ 设置警告标志
On Error Resume Next
Win_Path = String(145, 0)
i = GetWindowsDirectory(Win_Path, 145)
Win_Path = Left(Win_Path, i)
i = sndPlaySound(Win_Path + "\Media\Ding.wav", &H1) “ 发出报警声音
On Error GoTo 0
Else
If Picture1.Visible = True Then Picture1.Visible = False
End If
Last_Num_Of_Entries = TCP1.dwNum_Of_Entries
Select Case Return1 “ 判断返回值
Case 0&:
Text1 = "": Combo1.Clear
For i = 0 To TCP1.dwNum_Of_Entries - 1
Tmp3 = Str(i + 1) + " "
Select Case TCP1.TCP_Table(i).dwState “ 显示连接状态
Case 1: Tmp3 = Tmp3 + "CLOSED"
Case 2: Tmp3 = Tmp3 + "LISTENING"
Case 3: Tmp3 = Tmp3 + "SYN_SENT"
Case 4: Tmp3 = Tmp3 + "SYN_RCVD"
Case 5: Tmp3 = Tmp3 + "ESTABLISHED"
Case 6: Tmp3 = Tmp3 + "FIN_WAIT1"
Case 7: Tmp3 = Tmp3 + "FIN_WAIT2"
Case 8: Tmp3 = Tmp3 + "CLOSE_WAIT"
Case 9: Tmp3 = Tmp3 + "CLOSING"
Case 10: Tmp3 = Tmp3 + "LAST_ACK"
Case 11: Tmp3 = Tmp3 + "TIME_WAIT"
Case 12: Tmp3 = Tmp3 + "DELETE_TCB"
End Select
Combo1.AddItem Tmp3 “ 充实列表以供用户删除
Tmp3 = Tmp3 + ":" + vbCrLf + vbTab + "Local: " “ 本地IP
CopyMemory Ip_Buf(1), TCP1.TCP_Table(i).dwLocalAddr, 4
Tmp3 = Tmp3 + CStr(Ip_Buf(1)) + "." + CStr(Ip_Buf(2)) + "." _
+ CStr(Ip_Buf(3)) + "." + CStr(Ip_Buf(4))
Tmp1 = TCP1.TCP_Table(i).dwLocalPort “ 本地端口
Tmp2 = Tmp1 / 256 + (Tmp1 Mod 256) * 256
Tmp3 = Tmp3 + ":" + Str(Tmp2) + vbTab + "Remote: " “ 远程IP
CopyMemory Ip_Buf(1), TCP1.TCP_Table(i).dwRemoteAddr, 4
Tmp3 = Tmp3 + CStr(Ip_Buf(1)) + "." + CStr(Ip_Buf(2)) + "." _
+ CStr(Ip_Buf(3)) + "." + CStr(Ip_Buf(4))
Tmp1 = TCP1.TCP_Table(i).dwRemotePort “ 远程端口
Tmp2 = Tmp1 / 256 + (Tmp1 Mod 256) * 256
Tmp3 = Tmp3 + ":" + Str(Tmp2) + vbCrLf
Text1 = Text1 + Tmp3
Next i
Case 50&:
MsgBox "系统不支持该API函数": End
Case 87:
MsgBox "无效的参数": End
Case 111&:
MsgBox "缓冲区溢出": End
Case 232&:
MsgBox "无数据": End
End Select
End Sub
Private Sub 删除该连接_Click()
Dim Return1 As Long
If Combo1.ListIndex < 0 Then Exit Sub
“ 将欲删连接的状态置为MIB_TCP_STATE_DELETE_TCB(值为12)
TCP1.TCP_Table(Combo1.ListIndex).dwState = 12
Return1 = SetTcpEntry(TCP1.TCP_Table(Combo1.ListIndex)) “ 执行删除
If Return1 = 0 Then
MsgBox "成功删除当前连接"
Else
MsgBox "删除连接失败"
End If
Timer1_Timer
End Sub

点击这里下载EXE文件。