European Governments Targeted in Roundcube Email Server Hacking Campaign: Winter Vivern Strikes Again

3 min read
European Governments Targeted in Roundcube Email Server Hacking Campaign: Winter Vivern Strikes Again

In the world of cybersecurity, the battle between malicious actors and defenders rages on. One of the latest chapters in this ongoing saga involves the Winter Vivern Russian hacking group, which has been exploiting a Roundcube Webmail zero-day vulnerability to target European government entities and think tanks. This blog will delve into the details of this alarming cyberattack and its potential implications.

The Roundcube Zero-Day Exploitation

Since at least October 11, the Winter Vivern group has been leveraging a zero-day vulnerability in Roundcube Webmail, a popular web-based email platform. The vulnerability, identified as Stored Cross-Site Scripting (XSS) and assigned CVE-2023-5631, was first reported by ESET researchers on October 16.

The security patches to address this vulnerability were released five days after ESET's discovery. The cyberespionage group, also known as TA473, had been using this vulnerability to send HTML email messages containing carefully crafted SVG documents. These documents enabled them to remotely inject arbitrary JavaScript code into victims' browsers.

Phishing with a Purpose

The attackers used cleverly disguised phishing emails, impersonating the "Outlook Team," in an attempt to lure victims into opening these malicious emails. Upon opening the email, a first-stage payload was triggered, exploiting the Roundcube email server vulnerability. This vulnerability allowed the attackers to inject JavaScript code into the victim's browser, ultimately granting them access to the targeted email accounts.

The final JavaScript payload dropped during these attacks enabled the malicious actors to harvest and steal emails from the compromised webmail servers. This technique was highly effective as it required no manual intervention beyond simply viewing the malicious message in a web browser.

Winter Vivern's Previous Activities

Winter Vivern is not a newcomer to the world of cyberespionage. The group first appeared in April 2021 and has since garnered attention for its deliberate targeting of government entities worldwide, including India, Italy, Lithuania, Ukraine, and even the Vatican. Its objectives align closely with the interests of the governments of Belarus and Russia.

Interestingly, Winter Vivern had previously targeted Zimbra and Roundcube email servers owned by governmental organizations since at least 2022. In these attacks, the group exploited known vulnerabilities in Roundcube and Zimbra, for which proofs of concept were readily available online.

Implications for European Governments

The Winter Vivern group's persistent and regular phishing campaigns, combined with the failure of many internet-facing applications to receive regular updates, make it a significant threat to governments in Europe. This latest zero-day exploitation in Roundcube emphasizes the need for cybersecurity diligence and proactive measures to protect sensitive government information.


The Winter Vivern Russian hacking group's exploitation of the Roundcube zero-day vulnerability is a stark reminder of the ever-present threat to government entities and organizations with sensitive data. The evolving tactics of cybercriminals underscore the importance of maintaining robust cybersecurity practices and staying vigilant against the latest threats. European governments, along with entities worldwide, must invest in proactive security measures to protect their valuable data from malicious actors like Winter Vivern.

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