0x01漏洞描述

CVE-2020-0796是存在于微软服务器SMB协议中的一个“蠕虫化”漏洞，该漏洞未包含 在微软本月发布的补丁中，是在补丁的序言中泄露的。目前微软尚未发布任何技术详情，思科Talos团队和Fortinet公司提供了简短概述，目前尚不清楚该漏洞的补丁何时发布。
Fortinet公司指出，该漏洞是“微软 SMB 服务器中的一个缓冲区溢出漏洞”，严重等级为最高评分，“该漏洞由易受攻击的软件错误地处理恶意构造的压缩数据包而触发。远程、未经认证的攻击者可利用该漏洞在该应用程序的上下文中执行任意代码。”

      漏洞公告显示，SMB 3.1.1协议中处理压缩消息时，对其中数据没有经过安全检查，直接使用会引发内存破坏漏洞，可能被攻击者利用远程执行任意代码。攻击者利用该漏洞无须权限即可实现远程代码执行，受黑客攻击的目标系统只需开机在线即可能被入侵。 
思科Talos博客文章也给出了类似描述，不过随后将其删除。

思科指出,“利用该漏洞可导致系统遭蠕虫攻击，也就是说漏洞可轻易地在受害者之间传播。”

0x02漏洞编号

CVE-2020-0796

0x03漏洞等级

严重

0x04影响范围

Windows 10 Version 1903 for 32-bit Systems
Windows 10 Version 1903 for x64-based Systems
Windows 10 Version 1903 for ARM64-based Systems
Windows Server, version 1903 (Server Core installation)
Windows 10 Version 1909 for 32-bit Systems
Windows 10 Version 1909 for x64-based Systems
Windows 10 Version 1909 for ARM64-based Systems
Windows Server, version 1909 (Server Core installation)

0x05漏洞原理

    漏洞发生在srv2.sys中,由于SMB没有正确处理压缩的数据包,在解压数据包的时候使用客户端传过来的长度进行解压时,并没有检查长度是否合法.最终导致整数溢出。

SMB v3中支持数据压缩,如果SMB Header中的ProtocolId为0x424D53FC也就是0xFC, ‘S’, ‘M’, ‘B’.那么就说明数据是压缩的,这时smb会调用压缩解压处理的函数.

首先SMB会调用srv2!Srv2ReceiveHandler函数接收smb数据包，并根据ProtocoIId设置对应的处理函数。

  __int64 __fastcall Srv2ReceiveHandler(__int64 a1, void *Src, __int64 a3, unsigned int a4, unsigned int *a5, char *Srca, struct _SLIST_ENTRY *a7, _QWORD *a8) {     ...     //     // 这里判断头部ProtocolId     //      if ( **((_DWORD **)&v20[15].Next[1].Next + 1) == 'BMSxFC' )       {         if ( KeGetCurrentIrql() > 1u )         {           v20[14].Next = (_SLIST_ENTRY *)v11;           v20[2].Next = (_SLIST_ENTRY *)Srv2DecompressMessageAsync;           v43 = HIDWORD(v20->Next) == 5;           *((_DWORD *)&v20[3].Next + 2) = 0;           if ( v43 )           {             LOBYTE(v71) = 1;             LOBYTE(v35) = 1;             SRV2_PERF_ENTER_EX(&v20[32].Next + 1, v35, 307i64, "Srv2PostToThreadPool", (_DWORD)v71);           }           v44 = *((_QWORD *)&v20[3].Next[8].Next + 1);           v45 = *(_QWORD *)(v44 + 8i64 * KeGetCurrentNodeNumber() + 8);           if ( !ExpInterlockedPushEntrySList((PSLIST_HEADER)(v45 + 16), v20 + 1) && *(_WORD *)(v45 + 66) )             RfspThreadPoolNodeWakeIdleWorker(v45);           goto LABEL_168;             }         } } 

产生整数溢出漏洞的代码如下：

  __int64 __fastcall Srv2DecompressData(__int64 pData) {   __int64 v2; // rax   COMPRESSION_TRANSFORM_HEADER Header; // xmm0 MAPDST   __m128i v4; // xmm0   unsigned int CompressionAlgorithm; // ebp   __int64 UnComparessBuffer; // rax MAPDST   int v9; // eax   int v11; // [rsp+60h] [rbp+8h]   v11 = 0;   v2 = *(_QWORD *)(pData + 0xF0);   if ( *(_DWORD *)(v2 + 0x24) < 0x10u )         // 这里判断数据包长度的最小值     return 0xC000090Bi64;   Header = *(COMPRESSION_TRANSFORM_HEADER *)*(_QWORD *)(v2 + 0x18);// [v2+0x18]中为客户端传进来的Buffer                                                 // [v2+0x24]为数据包长度   v4 = _mm_srli_si128((__m128i)Header, 8);   CompressionAlgorithm = *(_DWORD *)(*(_QWORD *)(*(_QWORD *)(pData + 0x50) + 0x1F0i64) + 0x8Ci64);   if ( CompressionAlgorithm != v4.m128i_u16[0] )     return 0xC00000BBi64;                         UnCompressBuffer = SrvNetAllocateBuffer((unsigned int)(Header.OriginalCompressedSegmentSize + v4.m128i_i32[1]), 0i64);// OriginalCompressedSegmentSize + CompressedSegmentSize，这里没有检查相加的值，导致整数溢出，分配一个较小的UnCompressBuffer   if ( !UnComparessBuffer )     return 0xC000009Ai64;   if ( (int)SmbCompressionDecompress(               CompressionAlgorithm,             // CompressionAlgorithm               *(_QWORD *)(*(_QWORD *)(pData + 0xF0) + 0x18i64) + (unsigned int)Header.Length + 0x10i64,// CompressedBuffer               (unsigned int)(*(_DWORD *)(*(_QWORD *)(pData + 0xF0) + 0x24i64) - Header.Length - 0x10),// CompressedBufferSize               (unsigned int)Header.Length + *(_QWORD *)(UnComparessBuffer + 0x18),// UncompressedBuffer，会传入SmbCompressionDecompress函数进行Decompress处理。               Header.OriginalCompressedSegmentSize,               &v11) < 0     || (v9 = v11, v11 != Header.OriginalCompressedSegmentSize) )   {     SrvNetFreeBuffer(UnComparessBuffer);     return 0xC000090Bi64;   }   if ( Header.Length )   {     memmove(       *(void **)(UnComparessBuffer + 24),       (const void *)(*(_QWORD *)(*(_QWORD *)(pData + 240) + 24i64) + 16i64),       (unsigned int)Header.Length);     v9 = v11;   }   *(_DWORD *)(UnComparessBuffer + 36) = Header.Length + v9;   Srv2ReplaceReceiveBuffer(pData, UnComparessBuffer);   return 0i64; }

0x06漏洞检测

       已经很多的验证脚本，整体的思路都是验证回包中的特定位置是否包含十六进制的x11x03或x02x00这两个关键字。在存在漏洞的SMB版本的通信回包如下：

python3版POC

  import socket import struct import sys from netaddr import IPNetwork  pkt = b'x00x00x00xc0xfeSMB@x00x00x00x00x00x00x00x00x00x1fx00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00$x00x08x00x01x00x00x00x7fx00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00xx00x00x00x02x00x00x00x02x02x10x02"x02$x02x00x03x02x03x10x03x11x03x00x00x00x00x01x00&x00x00x00x00x00x01x00 x00x01x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x03x00nx00x00x00x00x00x01x00x00x00x01x00x00x00x01x00x00x00x00x00x00x00'  subnet = sys.argv[1]  for ip in IPNetwork(subnet):      sock = socket.socket(socket.AF_INET)     sock.settimeout(3)      try:         sock.connect(( str(ip),  445 ))     except:         sock.close()         continue      sock.send(pkt)      nb, = struct.unpack(">I", sock.recv(4))     res = sock.recv(nb)     if res[68:70] != b"x11x03" or res[70:72] != b"x02x00":         print(f"{ip} Not vulnerable.")     else:         print(f"{ip} Vulnerable")

也可以使用nmap的脚本进行验证，依托nmap的强大框架，更方便。

  local smb = require "smb" local stdnse = require "stdnse" local nmap = require "nmap"  description = [[ smb-protocols script modified to apply check for CVE-2020-0796 by psc4re.  Attempts to list the supported protocols and dialects of a SMB server. Packet check based on https://github.com/ollypwn/SMBGhost/ The script attempts to initiate a connection using the dialects: * NT LM 0.12 (SMBv1) * 2.02       (SMBv2) * 2.10       (SMBv2) * 3.00       (SMBv3) * 3.02       (SMBv3) * 3.11       (SMBv3) Additionally if SMBv1 is found enabled, it will mark it as insecure. This script is the successor to the (removed) smbv2-enabled script. ]]  --- -- @usage nmap -p445 --script smb-protocols <target> -- @usage nmap -p139 --script smb-protocols <target> -- -- @output -- | smb-protocols: -- |   dialects: -- |     NT LM 0.12 (SMBv1) [dangerous, but default] -- |     2.02 -- |     2.10 -- |     3.00 -- |     3.02 -- |_    3.11 (SMBv3.11) compression algorithm - Vulnerable to CVE-2020-0796 SMBGhost -- -- @xmloutput -- <table key="dialects"> -- <elem>NT LM 0.12 (SMBv1) [dangerous, but default]</elem> -- <elem>2.02</elem> -- <elem>2.10</elem> -- <elem>3.00</elem> -- <elem>3.02</elem> -- <elem>3.11 (SMBv3.11) [Potentially Vulnerable to CVE-2020-0796 Coronablue]</elem> -- </table> ---  author = "Paulino Calderon (Modified by Psc4re)" license = "Same as Nmap--See https://nmap.org/book/man-legal.html" categories = {"safe", "discovery"}  hostrule = function(host)   return smb.get_port(host) ~= nil end  action = function(host,port)   local status, supported_dialects, overrides   local output = stdnse.output_table()   overrides = {}   status, supported_dialects = smb.list_dialects(host, overrides)   if status then     for i, v in pairs(supported_dialects) do -- Mark SMBv1 as insecure       if v == "NT LM 0.12" then         supported_dialects[i] = v .. " (SMBv1) [dangerous, but default]"       end       if v == "3.11" then         local msg          local response         local compresionalg         local comp         msg = 'x00x00x00xc0xfeSMB@x00x00x00x00x00x00x00x00x00x1fx00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00$x00x08x00x01x00x00x00x7fx00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00xx00x00x00x02x00x00x00x02x02x10x02"x02$x02x00x03x02x03x10x03x11x03x00x00x00x00x01x00&x00x00x00x00x00x01x00 x00x01x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x03x00nx00x00x00x00x00x01x00x00x00x01x00x00x00x01x00x00x00x00x00x00x00'         local socket = nmap.new_socket()         socket:set_timeout(3000)         socket:connect(host.ip,445)         socket:send(msg)         response,data = socket:receive()         compressionalg=  string.sub(data,-2)             if compressionalg == "x01x00" then           comp = "LZNT1 compression algorithm - Vulnerable to CVE-2020-0796 SMBGhost"         elseif compressionalg == "x02x00" then           comp ="LZ77 compression algorithm - Vulnerable to CVE-2020-0796 SMBGhost"         elseif compressionalg == "x00x00" then           comp ="No Compression Not Vulnerable"         elseif compressionalg == "x03x00" then           comp="LZ77+Huffman compression algorithm - Vulnerable to CVE-2020-0796 SMBGhost"         end         supported_dialects[i] = v .." " .. comp       end     end     output.dialects = supported_dialects   end    if #output.dialects>0 then     return output   else     stdnse.debug1("No dialects were accepted")     if nmap.verbosity()>1 then       return "No dialects accepted. Something may be blocking the responses"     end   end end

github 上面有人把扫描 CVE-2020-0796 的脚本给写了出来。

项目地址：https://github.com/ollypwn/SMBGhost

  import socket import struct import sys   pkt = b'x00x00x00xc0xfeSMB@x00x00x00x00x00x00x00x00x00x1fx00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00$x00x08x00x01x00x00x00x7fx00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00xx00x00x00x02x00x00x00x02x02x10x02"x02$x02x00x03x02x03x10x03x11x03x00x00x00x00x01x00&x00x00x00x00x00x01x00 x00x01x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x00x03x00nx00x00x00x00x00x01x00x00x00x01x00x00x00x01x00x00x00x00x00x00x00' sock = socket.socket(socket.AF_INET) sock.settimeout(3) sock.connect(( sys.argv[1],  445 )) sock.send(pkt)   nb, = struct.unpack(">I", sock.recv(4)) res = sock.recv(nb)   if not res[68:70] == b"x11x03":     exit("Not vulnerable.") if not res[70:72] == b"x02x00":     exit("Not vulnerable.")   exit("Vulnerable.")

可以选择禁用SMBv3压缩来保护服务器免受攻击

 Set-ItemProperty -Path "HKLM:SYSTEMCurrentControlSetServicesLanmanServerParameters" DisableCompression -Type DWORD -Value 1 -Force

0x07漏洞加固

1. 更新，完成补丁的安装。

操作步骤：设置->更新和安全->Windows更新，点击“检查更新”。

2.微软给出了临时的应对办法：

运行regedit.exe，打开注册表编辑器，在HKLMSYSTEMCurrentControlSetServicesLanmanServerParameters建立一个名为DisableCompression的DWORD，值为1，禁止SMB的压缩功能。

3.对SMB通信445端口进行封禁。

补丁链接

https://catalog.update.microsoft.com/v7/site/Search.aspx?q=KB4551762 

参考链接

https://blogs.360.cn/post/CVE-2020-0796.html

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/ADV200005

转载请注明：Adminxe’s Blog » CVE-2020-0796 SMB远程代码执行漏洞 分析、验证及加固