Block spoofing emails

Hi,

I recommend setting SPF-records for your domain and enabling "Perfom SPF check" in SMTP->Antispam.

Hi Josef, thank you for your reply. 

SPF is always enabled and records are update-to-date, this seems to be an open relay problem in UTM.

Hi Josef, I know we use "Softfail", but we have "Perform SPF check" turned on and I can see a lot of emails got rejected because of SPF check failed.

I still think we have is an open relay problem, not an SPF problem.

If you don't check your own mail logs after doing the OpenRelay test, you would never really know this.

PS: and i think SPF soft-fail will pass UTM-Spam filter. (you may check SPF-records from SPF-blocked mails)

As said the UTM will not reject when the SPF-policy is set to Softfail, this is documented in the link I posted.

All the mails which you see rejecting for sure have a Hardfail SPF-policy. Your Domain have a Softfail-policy, so the mails got not rejected. The Feature "Perform SPF check" just enable the check general.

Good morning, Johnny.  You got the answer from both Dirk and Josef.

Cheers - Bob

Apologies for the late reply.

Unfortunately, the solutions proposed didn't work, we updated SPF to "hard fail" but it still doesn't stop the phishing emails.

Here is the email header looks like -

Received: from EX2016-MDB-AN.xxx.hosted (10.2.4.129) by
 EX2016-MDB-AN.xxx.hosted (10.2.4.129) with Microsoft SMTP Server
 (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2308.8
 via Mailbox Transport; Wed, 20 Jul 2022 14:15:40 +1000
Received: from EX2016-MDB-AN.xxx.hosted (10.2.4.129) by
 EX2016-MDB-AN.xxx.hosted (10.2.4.129) with Microsoft SMTP Server
 (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id
 15.1.2308.8; Wed, 20 Jul 2022 14:15:40 +1000
Received: from ip-10-2-3-109.ap-xxxx.compute.internal (10.2.5.109) by
 EX2016-MDB-AN.xxx.hosted (10.2.4.129) with Microsoft SMTP Server
 (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2308.8
 via Frontend Transport; Wed, 20 Jul 2022 14:15:40 +1000
Received: from [10.2.4.120] (helo=mail.xxx.com)
	by ip-10-2-3-109.ap-southeast-2.compute.internal with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256)
	(Exim 4.90_1)
	(envelope-from <user@xxx.com>)
	id 1oE17c-0004qV-OG
	for user@xxx.com; Wed, 20 Jul 2022 14:15:40 +1000
Received: from [185.222.58.69] (port=62467 helo=xxx.com)
	by mail.xxx.com with esmtp (Exim 4.95)
	(envelope-from <user@xxx.com>)
	id 1oE17W-0001WW-0x
	for user@xxx.com;
	Wed, 20 Jul 2022 14:15:34 +1000
From: xxx.com Server <user@xxx.com>
To: <user@xxx.com>
Subject: Three (4) Incoming mails not delivered
Date: Wed, 20 Jul 2022 06:15:30 +0200
Message-ID: <20220720061530.C5379167367D62FD@xxx.com>
MIME-Version: 1.0
Content-Type: text/html; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
Return-Path: user@xxx.com
X-MS-Exchange-Organization-Network-Message-Id: e0bd540b-123e-4816-8107-08da6a0681e5
X-MS-Exchange-Organization-AVStamp-Enterprise: 1.0
X-MS-Exchange-Organization-AuthSource: EX2016-MDB-AN.xxx.hosted
X-MS-Exchange-Organization-AuthAs: Anonymous
X-MS-Exchange-Transport-EndToEndLatency: 00:00:00.1880204
X-MS-Exchange-Processed-By-BccFoldering: 15.01.2308.008

Received: from [185.222.58.69] (port=62467 helo=xxx.com)
by mail.xxx.com with esmtp (Exim 4.95)
(envelope-from <user@xxx.com>)
id 1oE17W-0001WW-0x
for user@xxx.com;
Wed, 20 Jul 2022 14:15:34 +1000

The first "Received: from [185.222.58.69]" is not in the SPF record, yet it is the IP that the email originated from.

Hi,

send me a PM with the real log.

Josef will help you.  The line we would need to see is the one where the SMTP Proxy receives the email.  That line would be above those you posted.

     Received: from mail-dm6nam10on2109.outbound.protection.outlook.com ([40.107.93.109]:27105 helo=NAM10-DM6-obe.outbound.protection.outlook.com)
         by xxxxx.mediasoftusa.com with esmtps

The above came from a client at a company that hosts their email with outlook.  40.107.93.109 is included in the SPF record for spf.protection.outlook.com.

Cheers - Bob

Thank you all, I have sent a pm to Josef.

We received another phishing attack, the attacker managed to pass the SPF check

 Authentication-Results: wps01.wadax.ne.jp;
spf=pass (sender IP is 18.119.141.193) smtp.mailfrom=abc@xxx.com smtp.helo=[127.0.0.1]
Received-SPF: pass (wps01.wadax.ne.jp: connection is authenticated)

I have no idea how they could they do that? the IP is probably in one of these includes

include:spf.messagelabs.com include:spf.protection.outlook.com include:spf.smtp2go.com

Phishing attacks are rarely stopped by SPF.  Most are done with an account that was hijacked or from a new account at an email provider like Gmail - Google seems to be the email of choice for online criminals.  The best defense against phishing is anti-phishing training for your organization, like Sophos Phish Threat.

Note that that the content of the From field in an email can be spoofed instead of being the same as the Sender.  This is likely what happened to your coworkers as described in your opening post in this thread.

Cheers - Bob

Thanks Bob, appreciate your reply.

My understanding is that the From field in an email can be spoofed, but that will make it different to the Return-Path field, therefore, SPF comes into play.

In our case, the  From field and the Return-Path field are the same address, and the SPF check was passed -

Authentication-Results: wps01.wadax.ne.jp;
spf=pass (sender IP is 18.119.141.193) smtp.mailfrom=abc@xxx.com smtp.helo=[127.0.0.1]
Received-SPF: pass (wps01.wadax.ne.jp: connection is authenticated)

This makes me think about why Sophos could let the email through, and how did the scammer manage to pass the SPF check.

Thanks Bob, appreciate your reply.

My understanding is that the From field in an email can be spoofed, but that will make it different to the Return-Path field, therefore, SPF comes into play.

In our case, the  From field and the Return-Path field are the same address, and the SPF check was passed -

Authentication-Results: wps01.wadax.ne.jp;
spf=pass (sender IP is 18.119.141.193) smtp.mailfrom=abc@xxx.com smtp.helo=[127.0.0.1]
Received-SPF: pass (wps01.wadax.ne.jp: connection is authenticated)

This makes me think about why Sophos could let the email through, and how did the scammer manage to pass the SPF check.

The SPF record for wps01.wadax.ne.jp uses ~all instead of -all, Johnny, so SPF is not enforced for that domain.

I think we all read past the spot where you set your SPF to hard fail several days ago - that only affects how others treat mail from your domain.

Have you sent Josef the full log?

Cheers - Bob

UTM does not have tools to prevents such attacks. Only Central Email can deal with such BECs (business email compromise) attacks. 

Also see: ai.sophos.com/.../