Attention Federal Agencies: DMARC is Not a Silver Bullet for Email Security


DMARC is just one small piece to the very complicated email security puzzle.

As part of the government’s broader initiative to harden email security, federal agencies are scrambling to meet the Oct. 16 deadline established by the Homeland Security Department to implement the Domain-based Message Authentication, Reporting and Conformance protocol, known as DMARC. The binding operational directive issued nearly 12 months ago is intended to provide strong protections so that spoofed domains are rejected at the server.

The government’s decision to go all in on DMARC is practical in theory but confounding to many in security community who recognize the protocol as anything but a silver bullet for email security. After all, the sole purpose of DMARC is to validate exact domains in order to prevent domain spoofing attacks. While doing so can marginally reduce the number of advanced phishing attacks, the protocol does nothing to protect against the more commonly deployed business email compromise techniques, such as display name spoofing and domain impersonations.

There’s been so much hype around DMARC adoption that there is a real fear that a false sense of security is proliferating among federal agencies as they work to comply, and it is unclear as to whether those responsible for email hygiene fully understand that DMARC is just one small piece to the very complicated email security puzzle.

Rejecting Fraudulent Messages

DMARC was first launched in 2012 to better detect and prevent email spoofing. It is built on the DomainKeys Identified Mail and Sender Policy Framework and offers linkage to the sender’s domain name, reporting, and policies on how to handle authentication failures. When implemented by both sender and receiver, DMARC can help foil domain spoofing and enables organizations to filter out and reduce the number of fraudulent emails.  

Homeland Security is correct in that DMARC can be effective in filtering out some fraudulent emails. However, being that the underlying responsibility of DMARC is policy enforcement, the protocol is not designed to prevent, detect or respond to popular social engineering techniques (spear-phishing, pretexting and whaling) or impersonation attacks, such as the infamous CEO spoofing which uses display name spoofing and cousin domain spoofing techniques. Such threats are far more common, cost-effective and executable, and all are beyond DMARC’s control.

A Limited Solution Only Solves a Small Part of a Complex Problem

While DMARC is a step in the right direction, it is far from being a comprehensive answer to the government's email security problems.

For DMARC to work as intended, both the sender and the receiver need to implement it correctly. But even if they have, exact domain spoofing attacks can exploit vulnerabilities in email clients to mislead end users on the validity of a message. In a direct spoofing attack, an adversary can exploit a vulnerability in a web browser or in a code to change the return path details. Mailsploit, one of the latest and most dangerous phishing techniques, can easily render DMARC obsolete by exploiting how mail servers handle text data differently than operating systems. In other words, government agencies could remain at risk of exact domain spoofing whether or not they have implemented DMARC appropriately.

Even when it is effective, DMARC can be cumbersome. It often leaves some organizations accidentally rejecting legitimate messages, and it can also break a company’s mail flow by creating a backlog of messages. DMARC is also very complicated to configure with many cloud-based solutions and can require significant maintenance beyond authorization

New Technologies for Complex Threats

DMARC was designed with one function in mind, to weed out exact domain spoofing attacks. For example, would be challenging to spoof with DMARC in place. But today’s attackers—especially those targeting government agencies—are able to bypass the protocol with relative ease.

Relying too much on DMARC puts too many of one’s eggs in a single cybersecurity basket and can lull federal organizations and businesses into a false sense that they’re entirely protected from phishing attacks. In the whack-a-mole game of security, every time a new solution comes online, hackers eventually find a way to circumvent it. DMARC is no different and must be supplemented with additional layers of email security to truly make a dent in the risk landscape.

Implementing security that can identify messages after they have landed in the inbox can help close the vulnerability gap. New advances in artificial intelligence and machine learning can enable organizations to monitor every person's inbox and learn about the user’s communication habits, offering an enhanced level of protection, as well as a layer of detection and response. Users can even be alerted through inbox messages while the machines and security teams can collect information useful for intelligence sharing and threat identification.

DMARC is an important part of the puzzle, but it’s only a small piece. Homeland Security and government agencies must recognize this reality and not fall into a false sense of security. The stakes are far too high to mistakenly think that DMARC is some sort of email security silver bullet.

Eyal Benishti is the founder and chief executive officer of IRONSCALES.