Mass Phishing Campaign Attacking Zimbra email users’ to Steal Login Credentials

A group of researchers recently published a significant mass-spreading phishing campaign. It targets Zimbra account users, shedding light on a campaign that has been active since April 2023.

This article delves into the intricate details of this operation, highlighting its targets, methodology, and geographic impact.

A Stealthy Campaign Targeting Zimbra Users

Zimbra Collaboration, an open-core collaborative software platform, has become a sought-after alternative to enterprise email solutions. 

Cyber adversaries have orchestrated a cunning phishing campaign aimed at a diverse range of targets, including small and medium-sized businesses and governmental entities. 

ESET, a Slovak software company specializing in cybersecurity, reveals that Poland boasts the largest number of victims, encompassing European countries such as Ukraine, Italy, France, and the Netherlands. 

Moreover, Latin American nations, with Ecuador in the lead, have also fallen victim to this operation.

Countries hit by the campaign, according to ESET telemetry

The Attack Strategy

Despite not relying on cutting-edge technical sophistication, the campaign employs a blend of social engineering and user interaction to penetrate organizations utilizing Zimbra Collaboration. 

The approach involves luring targets with emails containing HTML attachments. 

These attachments house seemingly legitimate code, with a discreet link directing users to a malicious host. 

This clever tactic evades reputation-based anti-spam policies, offering a distinct advantage over conventional phishing methods that involve direct malicious links in the email body.

Viktor Šperka, an ESET researcher, emphasizes the simplicity and effectiveness of this technique, explaining, 

“Adversaries leverage the fact that HTML attachments contain legitimate code, with the only telltale element being a link pointing to the malicious host.” 

This stealthy approach allows the campaign to compromise organizations, highlighting its agility and adaptability successfully.

Unlike campaigns that zero in on specific verticals, this operation targets organizations connected solely by their use of Zimbra Collaboration. 


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The appeal of Zimbra to organizations with limited IT budgets renders it a consistent and attractive target for cyber adversaries.

Upon receipt of the email, the target is prompted to open the attached HTML file. 

The email often conveys urgency, warning recipients about server updates, account deactivation, or similar issues. 

This triggers the victim to click on the attachment, revealing a fake Zimbra login page customized to mimic the organization’s branding. 

Behind the scenes, the entered credentials are collected from the HTML form and dispatched to a server under the attacker’s control. 

With these stolen credentials, the adversary gains the potential to infiltrate the compromised email account.

The ongoing Zimbra phishing campaign is a stark reminder of the challenges organizations face in safeguarding sensitive information. 

Despite its apparent simplicity, the operation’s effectiveness underscores the importance of user education, advanced security measures, and proactive threat detection. 

As the cyber threat landscape evolves, vigilance and collaboration between security experts and organizations become paramount in mitigating these sophisticated attacks.

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Sujatha is a Cyber security content editor with a passion for creating captivating and informative content. With years of experience under her belt in Cyber Security, she is covering Cyber Security News, technology and other news.