Browser-hijacking malware talks to attackers using SPF email validation protocol

The technique makes malicious traffic harder to detect for firewalls and other network security systems, researcher says

A new Trojan program that displays rogue advertisements during browsing sessions uses a DNS-based email validation protocol called the Sender Policy Framework (SPF) in order to receive instructions from attackers without being detected, according to security researchers from Symantec.

The new malware is called Trojan.Spachanel and its purpose is to inject malicious JavaScript code into every Web page opened on infected computers, Symantec researcher Takashi Katsuki said Friday in a blog post.

The malware injects HTML script elements that load JavaScript files from remote URLs. The role of the JavaScript code is to display rogue advertisements inside pop-up windows and trick users to click on them, which generates income for the attackers, Katsuki said.

However, the most interesting aspect of this malware is the way in which it receives updated URLs from attackers to use in the rogue HTML script elements.

The malware periodically generates a domain name according to a predefined algorithm and makes an SPF lookup for it. Knowing in advance which domain will be generated, the attackers register it and configure its SPF record to contain IP (Internet Protocol) addresses or host names that will be used by the malware to construct new malicious URLs.

SPF was designed to detect email spoofing and is implemented using the DNS (Domain Name System).

A domain name owner can specify an SPF policy -- a number of IP addresses or host names that are allowed to send emails from that particular domain -- inside a DNS TXT or SPF record. Email servers can then perform SPF lookups via DNS in order to check that email messages appearing to have been sent from that domain actually came from an IP address authorized by the domain administrator.

If the sender IP address or host specified in an email's header is not listed in the SPF policy for the corresponding domain name then the email sender's address was probably spoofed.

In the case of Trojan.Spachanel, the SPF policy for the domain name is not used to validate emails, but to provide a new list of malicious host names to be used by the malware.

Using this technique, attackers can hide the malicious traffic from firewalls and other security products that might otherwise block direct connections to known malware command-and-control servers.

That's because in order to perform SPF lookups, the malware queries a trusted DNS server located on the local network or the Internet service provider's network. This server then queries other DNS servers up the chain until the request reaches the authoritative DNS server for the domain name, which responds with a TXT or SPF record containing the SPF policy.

"In some cases, specific domains are blocked by a local DNS server, but this malware generates a domain that is rarely filtered," Katsuki said.

Join the newsletter!

Or

Sign up to gain exclusive access to email subscriptions, event invitations, competitions, giveaways, and much more.

Membership is free, and your security and privacy remain protected. View our privacy policy before signing up.

Error: Please check your email address.

Tags malwarefirewallssymantecintrusionantispamDetection / prevention

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Lucian Constantin

IDG News Service
Show Comments

Cool Tech

Toys for Boys

Family Friendly

Stocking Stuffer

SmartLens - Clip on Phone Camera Lens Set of 3

Learn more >

Christmas Gift Guide

Click for more ›

Brand Post

Most Popular Reviews

Latest Articles

Resources

PCW Evaluation Team

Aysha Strobbe

Microsoft Office 365/HP Spectre x360

Microsoft Office continues to make a student’s life that little bit easier by offering reliable, easy to use, time-saving functionality, while continuing to develop new features that further enhance what is already a formidable collection of applications

Michael Hargreaves

Microsoft Office 365/Dell XPS 15 2-in-1

I’d recommend a Dell XPS 15 2-in-1 and the new Windows 10 to anyone who needs to get serious work done (before you kick back on your couch with your favourite Netflix show.)

Maryellen Rose George

Brother PT-P750W

It’s useful for office tasks as well as pragmatic labelling of equipment and storage – just don’t get too excited and label everything in sight!

Cathy Giles

Brother MFC-L8900CDW

The Brother MFC-L8900CDW is an absolute stand out. I struggle to fault it.

Luke Hill

MSI GT75 TITAN

I need power and lots of it. As a Front End Web developer anything less just won’t cut it which is why the MSI GT75 is an outstanding laptop for me. It’s a sleek and futuristic looking, high quality, beast that has a touch of sci-fi flare about it.

Emily Tyson

MSI GE63 Raider

If you’re looking to invest in your next work horse laptop for work or home use, you can’t go wrong with the MSI GE63.

Featured Content

Product Launch Showcase

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?