CVE-2021-26855-PoC

PoC exploit code for CVE-2021-26855.

Original code was developed by https://github.com/GreyOrder.

CVE-2021-26855 ssrf simple use of golang exercises Affected version

Exchange Server 2013 is less than CU23
Exchange Server 2016 is less than CU18
Exchange Server 2019 is less than CU7

Conditions of use

This vulnerability is different from previous exchange vulnerabilities. This vulnerability does not require a user identity that can log in. It can obtain internal user resources without authorization. It can be used with CVE-2021-27065 to implement remote command execution.

Vulnerability trigger requirements

Vulnerability in the target server
The target exchange server must be a load balancing server, that is, two or more servers are used at the same time
The target email address. Note that the address needs to be an email address in the domain instead of an email address. There is a difference between the two. After testing, it is not the case, as long as it is the correct email address, except in special circumstances
The attacker must also identify the Fully Qualified Domain Name (FQDN) of the internal Exchange server. In fact, only the server host name is required, because the host name can be resolved within the domain.

Among the above four items, FQDN can be captured by ntlm type2 message; email addresses can be directly enumerated. An additional explanation for FQDN, because I only use ntlm type2 to capture system information, the FQDN obtained by the tool by default is the currently accessed machine, so the vulnerability cannot be directly triggered. You need to manually judge based on the FQDN name and use -n to replace other exchanges. Server host name. Instructions for use

To exploit this vulnerability, it is more convenient to use a scripting language such as ruby ​​python. It is written in golang to learn golang, so this small tool can only be regarded as a semi-finished product and will be updated when there is time.

This tool currently supports the following functions:

Vulnerability detection (just simply check whether it can be hit, and it cannot be used for detection)
User enumeration
Simple mail id and subject reading
Mail download (upgraded, now a standard eml file)
Read the contacts saved by the user (note that it is not global, only the contacts saved by the target)
Folder specified, not arbitrary, please refer to https://docs.microsoft.com/en-us/exchange/client-developer/web-service-reference/distinguishedfolderid for details

For other uses, please modify the xml content yourself.

usage:

go run CVE-2021-26855-PoC.go -h

-h string required, target address or domain name

-U string Optional, need to enumerate user list

-d optional, download mail

-l Optional, list the mailing list

-n string is optional, you need to specify FQND to fill in

-t string Optional, request delay time (default "1")

-u string Optional, specify the target (default "administrator")

-c is optional, read the contacts saved by the current user, not all

-f string Optional, specify the folder to view (default "inbox")