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Russian hackers exploit new vulnerability
An advanced persistent threat (APT) group, known as Winter Vivern, previously associated with supporting Russia and Belarus, has been found exploiting a zero-day vulnerability in a widely-used webmail software. Security researchers discovered the cyber attack aiming at European governments through the Roundcube Webmail software.
Winter Vivern exploits zero-day in Roundcube
The latest campaign of the espionage group involved the use of a previously unknown bug affecting Roundcube, a free and open-source webmail application. Notably, the vulnerability comes with the potential for hackers to exfiltrate email messages without any manual intervention aside from viewing a harmful email message in a web browser. The vulnerability, tracked as CVE-2023-5631, was first revealed in mid-October by security researchers, with a patch subsequently released within two days.
Winter Vivern’s focus on surveillance
Commonly referred to as TA473, Winter Vivern's activities are majorly perceived to be linked with espionage. They are usually seen supporting the goals of Russia and Belarus. This has been notably apparent in the context of the ongoing conflict between Russia and Ukraine. The group has shown consistency in conducting targeted phishing campaigns, posing a significant threat to governmental entities in Europe.
Expanding Attacks
Winter Vivern has been active since 2020 and has specifically targeted government organizations across Europe and Central Asia. They utilize a range of malicious documents, phishing websites, and other tools to pierce through the cybersecurity barriers of their targets. Significantly, the group has previously hit Zimbra and Roundcube email servers, pointing out a consistent methodology in their attacks. Researchers linked Winter Vivern to another Belarus-based espionage group, known as MoustachedBouncer, in August.
Method of attack
Winter Vivern's method of attack carries a level of sophistication, utilizing known vulnerabilities accessible online and exploiting a zero-day vulnerability in Roundcube Servers to gain unauthorized access and compromize critical information.
Attack on Zimbra and Roundcube servers
Notably, Winter Vivern has consistently targeted Zimbra and Roundcube email servers, demonstrating their preference for governmental entities using these services. They leveraged known vulnerabilities that were accessible online in the software used by these entities, illustrating the group's methodical approach to its malicious operations.
Exploiting the CVE-2023-5631 Zero-day
In their latest attack, the APT group took advantage of a zero-day cross-site scripting (XSS) vulnerability, tracked as CVE-2023-5631, in Roundcube's widely utilized open-source webmail server. This flaw was previously undiscovered and unpatched, making it a potent tool in the hands of the attackers.
Injection of Malicious JavaScript Code
The XSS vulnerability in Roundcube's server allowed the malicious actor to inject harmful JavaScript code via craftily designed email messages. The unsuspecting victims, which mainly consisted of European governmental entities, were complicit in the attack as they unknowingly viewed these emails, triggering the execution of the malicious code. The success of this technique stressed the insidious nature of Winter Vivern's actions as they bypassed traditional security measures.
Implication of the attack
The attack orchestrated by the Winter Vivern group signifies a significant escalation in their operational capabilities. Their successful use of a zero-day vulnerability to infiltrate and extract sensitive information from government entities across Europe sheds light on the evolving landscape of cyber threats.
Gathering Information through Payload
The payloads used in the Winter Vivern-orchestrated attack were notably sophisticated. They were designed to systematically gather information from the victim's Roundcube accounts once the malicious email was viewed. The harvested data was then sent back to the hackers' command-and-control (C&C) server, establishing a covert two-way channel for ongoing data exploitation.
Timeline of the Zero-day Vulnerability Exploit
Winter Vivern began exploiting the zero-day vulnerability, CVE-2023-5631, as early as October 11. Due to the severity of the exploit, a patch was rapidly developed and released by October 16 to curtail further harmful activity. This swift response underscores the proactive steps being taken by security researchers and software developers to mitigate the impacts of these increasingly advanced cyberattacks.
