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Save Yourself From “Yourself”: Stop Spam From Your Own Address

Friday, September 22nd, 2017

I just got junk email … from me!

It is surprisingly common for users to receive Spam email messages that appear to come from their own address (i.e. “joe@domain.com” gets a Spam email addressed so it appears to be from “joe@domain.com”).  We discussed this issue tangentially in a previous posting: Bounce Back & BackScatter Spam – “Who Stole My Email Address”?  However, many users wonder how this is even possible, while others are concerned if their Spam filters are not catching these messages.

How can Spammers use your email address to send Spam?

The way that email works at a fundamental level, there is very little validation performed on the apparent identity of the “Sender” of an email.  Just as you could mail a letter at the post office and write any return address on it, a Spammer can compose and send an email address with any “From” email address and name.  This is in fact extremely easy to do, and Spammers use this facility with almost every message that they send.

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Tags: allow list, dkim, email address, filtering, forged email, sender, smtp, spam, spf, white list
Posted in LuxSci Library: The Technical Side of Email, Popular Posts
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ARC and SMTP MTA-STS: The State of Domain-based Email Authentication – Part 3

Tuesday, September 19th, 2017

We’ll close (for now) our three part series on the state of domain-based authentication for emails by completing the story on technologies being deployed or defined to improve the security of the email ecosystem. In Part 1, we wrote about using Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) to authenticate the sending mail server. Part 2 described how Domain-based Message Authentication, Reporting and Conformance (DMARC) is used to provide clear guidelines for the treatment of mail that fail SPF and/or DKIM authentication.

In this post, we’ll touch on two topics that are mature works in progress in the IETF, the technical standardization organization that has brought us so much of the protocols that govern the internet. The first technology is Authenticated Received Chain (ARC), defined to handle the shortcomings of SPF and DKIM when used with mail forwarders or mailing lists. The second technology is about correcting the lack of security between Message Transfer Agents (MTA), and a solution to enforce strict transport layer security for SMTP message transfer between MTAs.

It’s worth reiterating again that all these technologies are building blocks, and only when used and deployed collectively by the entire ecosystem can we hope to create the barriers needed to thwart fake emails and mail surveillance by malicious actors.

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Tags: ARC, dkim, DMARC, MTA, spf, ssl, STS
Posted in LuxSci Library: The Technical Side of Email
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DMARC: The State of Domain-based Email Authentication – Part 2

Monday, September 11th, 2017

Building a safer email ecosystem with DMARC

In our previous post, we described two techniques for authenticating an email sender:

  • Sender Policy Framework (SPF), IETF RFC 7208, which verifies if the sending MTA is indeed authorized to send mail on behalf of a domain; and
  • DomainKeys Identified Mail (DKIM), IETF RFC 6376, where a domain shows “ownership” of a mail it sends by signing portions of it so that critical aspects cannot be forged by intermediaries.

Like most technologies, these are just individual weapons in the arsenal for fighting phishing and spam. Weapons, like all tools, need to be properly used if they are to be effective. Unfortunately, as we described in the earlier post, both SPF and DKIM are deployed in a manner that reduces their usefulness. With SPF, the validation policy set by the sender is often chosen in a manner that leaves handling authentication failures at the discretion of the recipient. DKIM, on the other hand, does not even have an explicit policy directive set by the sender. Moreover, in a heterogeneous mail environment, some perfectly legitimate MTAs might not be capable of signing messages.

Building a safer email system with DMARC

Thus, receivers in actual deployments tend to “soft fail” any SPF and/or DKIM validation failures as there are reasonable situations when legitimate mail can fail such checks. A common example is forwarded mail (which fails SPF), or mail sent via a mailing list (which fails DKIM). Mail providers consider it better to deliver most mail (even if some are fake or spammy) rather than risk dropping legitimate mail. Thus, neither of these techniques individually or combined provide clear guidance to receivers, and the resulting actions can be inconsistent.

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Tags: dkim, DMARC, Domain-based Message Authentication, DomainKeys Identified Mai, email, Reporting and Conformance, sender policy framework, spf
Posted in LuxSci Library: The Technical Side of Email
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SPF and DKIM: The State of Domain-based Email Authentication – Part 1

Friday, September 1st, 2017

Recent reports on cyber-security threats in the healthcare sector by Verizon, Symantec and Ponemon consistently make several observations:

  • Email-borne malware is on the rise, with such malware delivered via spam or phishing;
  • Small-to-medium sized businesses (from all sectors) have the highest rate of email-delivered malware;
  • Most breaches are caused by negligent employees or contractors.

These conclusions are hardly surprising as email is now an increasingly common part of communications with protected health information (PHI) frequently exchanged amongst employees and patients within a practice, between medical providers, and medical providers and their business associates. The concern for the healthcare industry is the potential violation of the HIPAA privacy rule caused by email-related (and other) breaches, leading to disruptions from loss of data, compliance audits and possibly hefty fines.

No Phishing

We wrote about obvious measures medical providers can take to avoid HIPAA non-compliance in email exchanges such as opt-out email security. That addresses only one aspect of the threat landscape, though – the protection of PHI in email exchanges. Another aspect is more sinister, as it deals with external, malignant actors. These actors use various spoofing techniques to trick patients or employees of a medical practice to react incautiously, often impulsively, to emails supposedly coming from valid sources. These often lead to identity theft, where the damage is more far-reaching as the information given up is more long-lived and more widely used and cannot just be erased like revoking a misused credit card.

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Tags: DMARC, identity theft, phishing, sender, skim, spf
Posted in LuxSci Library: The Technical Side of Email
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Infographic: Steps to Avoiding Forged Email

Friday, February 12th, 2016

Forged emails are extremely common. Most of the time forged emails are merely a nuisance.However, if you accidentally share information with or click on a link from someone who sent a forged email, the results can devastate your goal or even your site, or if it’s really evil, an entire computer. Here’s some information about how to recognize and stop forged emails.

How to Avoid Forged Email: Forged Email Facts & SPF Significance

Avoiding Forged Email. Significance of SPF

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Tags: dkim, forged email, spam, spf
Posted in LuxSci Library: The Technical Side of Email
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