DMARC doesn't fix Phishing

Not a new thing, but a nice example just popped up in my inbox on my phone.

 
But FedEx solved their entire phishing problem when they published a strict p=reject DMARC record, right?
This didn’t come from fedex.com. It came from another domain that looks vaguely like fedex.com – what that domain is doesn’t matter, as the domain it’s sent from isn’t displayed to the user on my phone mail client. Nor is it displayed to the user by Mail.app on my desktop, unless you turn off Mail → Preferences … → Viewing → Use Smart Addresses.

That lookalike domain could pass SPF, it could be used as d= in DKIM signing, it could even be set up with DMARC p=reject. And the mail is pixel identical to real mail from fedex.com.
On my desktop client I can hover over the link and notice it looks suspicious – but it’s no more suspicious looking than a typical ESP link-tracking URL. And on mobile I don’t even get to do that.
SPF and DKIM and DMARC can temporarily inconvenience phishers to the extent that they have to change the domain they’re sending from, but it’ll have no effect on the vulnerability of most of your audience to being phished using your brand.

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Shibboleet

Using unique addresses for signups gives me the ability to track how well companies are protecting customer data. If only one company ever had an address, and it’s now getting spam or phishing mail, then that company has had a data breach. The challenge then becomes getting the evidence and details to the right people inside the company.
In one case it was easy. I knew a number of people inside the company and knew they would take it seriously and pass it on to the folks in the best place to deal with it. I did. They did. They got their systems secured and notified customers and it was all taken care of.
Other cases aren’t as easy.
Many years ago I got mail from my credit card company to a unique address. This was long before SPF or DKIM and the mail contained links different from the company’s main domain. I called them up to see if this was real or not. They told me it wasn’t, because tier 1 support are trained to tell users everything is suspicious. Eventually, though, it became clear this wasn’t a phish, it was just bad marketing by the company.
A few years ago I reported a possible breach to representatives of a company while at a meeting. Coincidentally, the address only their company had started getting phishing and spam during the conference. I brought it up to them and followed their directions for reporting. They asserted the leak wasn’t on their end, but to this day I get multiple spams a day to that address. They claimed that the spammer was someone I was friends with on their website, but they could never quite demonstrate that to my satisfaction. I treat that site as only marginally secure and take care with the information I share.
After Target was breached they emailed me, out of the blue, to the address I use at Amazon. There was some level of partnership between Amazon and Target and it appears Amazon shared at least part of their database with Target. I talked with security folks at Amazon but they told me they had no comment.
Of course, on the flip side, I know how challenging it is to sort through reports and identify the ones that are valid and ones that aren’t. When I handled abuse@ we had a customer that provided a music sharing program. If a connection was interrupted the software would attempt to reconnect. Sometimes the connection was interrupted because the modem dropped and a new person would get the IP address while the software was trying to reconnect. This would cause a flood of requests to the new person’s computer. These requests would set off personal firewalls and they’d contact abuse to tell us of hacking. There wasn’t any hacking, of course, but they’d still argue with us. One of my co-workers had a nickname for these folks that was somewhat impolite.
We had to implement some barriers to complaints to sort out the home users with personal firewalls from the real security experts with real firewalls that were reporting actual security issues. So I get that you don’t always want or need to listen to J. Random Reporter about a security issue.
Sometimes, though, J. Random Reporter knows what they’re talking about.

Yeah, I spent the morning trying to get support at a company to connect me to security or pass a message along. Too bad there isn’t a security shibboleet.

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ARC: Authenticated Received Chain

On Friday I talked a little about DMARC being a negative assertion rather than an authentication method, and also about how and when it could be deployed without causing problems. Today, how DMARC went wrong and a partial fix for it that is coming down the standards pipeline.
What breaks?

DMARC (with p=reject) risks causing problems any time mail with the protected domain in the From: field is either sent from a mailserver that is not under the control of the protected domain, or forwarded by a mailserver not under the control of the protected domain (and modified, however trivially, as it’s forwarded). “Problems” meaning the email is silently discarded.
This table summarizes some of the mail forwarding situations and what they break – but only from the original sender’s perspective. (If forwarding mail from a users mailbox on provider A to their mailbox on provider-Y breaks because of a DMARC policy on provider-A that’s the user’s problem, or maybe provider-A or provider-Y, but not the original sender’s.)

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Tools!

I just added a DMARC validation tool over on tools.wordtothewise.com.

You can give it a domain – such as ebay.com – and it will fetch the DMARC record, then explain and validate it. Or you can paste the DMARC record you’re planning to publish into it,  to validate it before you go live.
If you’ve not seen our tools page before, take a look. As well as DMARC we have a DKIM validator, SPF expander and optimizer, general DNS lookup tools, a bunch of RFCs covering all sorts of protocols, and base64 and quoted-printable decoders.
There’s also a widget that lets you add those little unicode pictures to your subject lines, whether you need a snowman ⛄, a forest ????, or a pig getting closer ???.
The results pages all have easily copyable URLs so they’re pretty good for sharing with co-workers or customers if you need that sort of thing.
(And if you need a cidr calculator, whois, or easy access to abuse.net & Microsoft SNDS check out Al’s xnnd.com.)

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