Sign1 Malware Campaign Compromises Thousands of WordPress Sites

A significant cybersecurity threat has emerged in the form of the Sign1 malware campaign, which has targeted over 39,000 WordPress sites in the last six months. This malicious campaign utilizes sophisticated techniques, including malicious JavaScript injections, to redirect unsuspecting users to scam sites, highlighting the evolving landscape of cyber threats facing website owners and visitors.

The Malware Operation

The Sign1 malware campaign, characterized by its use of rogue JavaScript injections, has recently infected an estimated 2,500 sites in just the past two months. This malware variant employs XOR-encoded JavaScript code that is decoded to execute a JavaScript file hosted on a remote server. This file, in turn, triggers redirects to a traffic distribution system operated by VexTrio, under specific conditions. Notably, the malware employs time-based randomization to fetch dynamic URLs, changing every 10 minutes to evade blocklists, with domains registered shortly before use in attacks.

Targeting Specific Visitors

A unique aspect of the Sign1 malware is its selective execution based on the visitor’s referral source. The malware specifically checks if the visitor arrived from major websites like Google, Facebook, Yahoo, or Instagram. If the referrer does not match these criteria, the malicious code remains dormant. Upon activation, visitors are redirected to scam sites through additional JavaScript executions from the same server, illustrating the intricate tactics employed by cybercriminals to deceive users.

Infiltration Techniques

The Sign1 campaign, initially identified in the latter half of 2023, has undergone multiple iterations, utilizing up to 15 different domains since July 31, 2023. While the exact method of compromise remains under investigation, it is suspected that WordPress sites are infiltrated through brute-force attacks or exploitation of vulnerabilities in plugins and themes. Attackers often embed malicious code within WordPress custom HTML widgets, leveraging plugins like Simple Custom CSS and JS to inject the malware discreetly, allowing it to evade detection for prolonged periods.


The Sign1 malware campaign represents a concerning trend in cyber threats, demonstrating the adaptability and persistence of malicious actors in targeting popular platforms like WordPress. Website owners are urged to maintain robust security measures, regularly update plugins and themes, and monitor for any suspicious activities to mitigate the risk of falling victim to such sophisticated malware campaigns. As cybersecurity threats continue to evolve, vigilance and proactive defense strategies are essential to safeguarding online assets and protecting users from falling prey to malicious activities.



About David Damstra

Business Leader and Business Developer, Project Manager and Full Stack Developer & Designer Creative Director, Brand Guardian, Minister of Company Culture Co-Author of Professional WordPress. Currently in Third Edition. Seasoned web developer using practical technology to rapidly create standards compliant dynamic websites. Experienced with web development, software development and systems and network management and consulting.