Phishers Try 'Text Direction Deception' Technique to Bypass Email Filters

Scammers can be pretty innovative when it comes to finding new ways to sneak phishing messages past secure email gateways and other filtering mechanisms.

One example is "text direction deception," a tactic where an attacker forces an HTML rendering engine to correctly display text that has been deliberately entered backward in the code — for example, getting text that exists in HTML code as "563 eciffO" to render forward correctly as "Office 365."

Security vendor Inky Technologies discovered the direction deception tactic being used in an email that was part of a phishing campaign. In a report this week, the company described the tactic as designed to trick security controls that filter email messages based on whether the emails contain text and text sequences that have been previously associated with phishing scams.

Such tactics could become more common as cybercriminals take advantage of the worldwide concern around the COVID-19 pandemic to fill email inboxes with phishing messages designed to trick users in various ways.

Just this week, for instance, Menlo Security reported what it described as a sophisticated, multistage phishing campaign targeted at stealing the credentials of specific individuals in the executive and finance teams at hundreds of companies.

The emails contained a phishing message that purported to be from the CEOs of each of the targeted companies. The emails also included an attachment that seemingly contained COVID-19 related employee information. The attachment contained a shortened link to a hosted form on a legitimate Microsoft service that prompted users for their login credentials.

With many email security products getting better at spotting scam emails, criminals have begun innovating as well. "To increase their success rate, attackers have adopted multi-stage attacks leveraging email, PDF attachments, and trusted SaaS services," Menlo said in its report. According to the security vendor, email users have been falling for such COVID-19 themed phishing emails in much larger numbers than with other phishing scams.

The rush to take advantage of COVID-19 fears is so high that some are dusting off old phishing kits and redeploying them again with a pandemic-themed lure. According to Akamai, its researchers have observed several threat actors recycling old phishing kits in new COVID-19 campaigns.

Innovative Tactics
Dave Baggett, CEO and co-founder of Inky, says he expects more criminals to use innovative tactics, such as text direction deception and other similar gambits, in COVID-19 related scams. As one example of another tactic, he points to COVID-19 scams where text in the HTML has the font size set to zero so it's effectively invisible to secure email gateways.

"This is just another method the attacker can use to hide text," he says of the text direction reversal method. "Anecdotally, it's used a lot less frequently than ordinary zero font, but that's probably because it will take a while for this tactic to find its way into phishing kits purveyed on the Dark Web."

Most secure email gateways use statistical models to learn the text sequences associated with legitimate email and that are associated with phishing, spam and other bad email, Inky said. "These models — the workhorse of mail protection since the 90s — learn, for example, that dollar signs in the subject line and 'make money fast!' in the body correlate with spam," the vendor said it its report.

Direction deception allows the attackers to thwart these pattern-matching capabilities by ensuring the text the email gateways are looking for doesn't appear in the HTML code. At the same time, the tactic ensures that email recipients see the text as perfectly normal, Inky said.

The security vendor described text direction deception as taking advantage of certain obscure capabilities in Cascading Style Sheets (CSS), a technology for describing how HTML documents are presented to the user. The capabilities pertain to how documents containing scripts like Arabic, which flows from the right to the left, and Latin are displayed. The specific property that the attackers abused allowed them to control how text is read and rendered, the vendor said.

Related Content:

Check out The Edge, Dark Reading's new section for features, threat data, and in-depth perspectives. Today's featured story: "Untangling Third-Party Risk (and Fourth, and Fifth...)."