Malwarebytes has observed a significant surge in malvertising incidents, reporting nearly 500 unique cases linked to Google search ads over the past year. Among these incidents, a particularly stealthy campaign has emerged that specifically targets users of the popular communication tool Slack. This campaign employs seemingly legitimate ads that appear above organic search results, effectively misleading users who search for Slack. Initially, clicking on the ad directed users to the official Slack website, creating an impression of authenticity. However, Malwarebytes suspected malicious intent and monitored the ad’s activity closely.
As the campaign evolved, the ad’s behavior changed significantly. It began to redirect users to a click tracker rather than the official Slack site, a tactic that exploits weaknesses in the Google ad ecosystem. By utilizing click tracking, the threat actor can obscure the final destination of users, thereby evading detection by Google’s security systems. The complexity of this ad chain makes it increasingly difficult for users and automated systems to evaluate its safety, allowing the attackers to maintain a low profile while facilitating malicious activities.
Eventually, the redirection led to a domain named slack-windows-download[.]com, which appeared to impersonate Slack but was created less than a week prior. This domain employed cloaking techniques, showing different content to different users based on their access or browsing behavior. Such tactics are designed to trick users into downloading malicious software disguised as legitimate Slack applications. The campaign demonstrates how threat actors can effectively manipulate ad systems to serve malicious content while appearing credible.
Upon further investigation, it was discovered that the download button on the impersonated page initiated a file download from another domain, hinting at connections to a broader campaign targeting software like Zoom. Analysis of the malware payload indicated a remote connection to a server previously associated with SecTopRAT, a remote access Trojan known for stealing sensitive information. This highlights the sophisticated nature of the malvertising campaign and serves as a warning to users about the risks associated with clicking on seemingly legitimate ads that may lead to harmful consequences.
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