Description

CVE-2024-27443 is a Cross-Site Scripting (XSS) vulnerability affecting Zimbra Collaboration (ZCS) versions 9.0 and 10.0. Specifically, the vulnerability resides within the CalendarInvite feature of the classic webmail interface, stemming from inadequate input validation when processing calendar headers. A malicious actor can inject a crafted calendar header containing an XSS payload into an email. When a user views this email in the Zimbra classic webmail interface, the embedded payload executes within the user's session, potentially enabling arbitrary JavaScript code execution. While the CVSS score is 6.1, the SOCRadar Vulnerability Risk Score (SVRS) is 60, indicating a medium level of risk. However, given the "Exploit Available" tag, "In The Wild" tag and CISA KEV tag, the real-world impact could be much higher.

Key Insights

• XSS Vulnerability: This is a classic XSS vulnerability that allows an attacker to inject malicious scripts into the victim's browser when they view the crafted email. This can lead to session hijacking, data theft, or even complete account takeover.
• Active Exploitation: Given that active exploits have been published and that it is used "In The Wild," the risk of exploitation is significantly elevated. Threat actors are actively leveraging this vulnerability, increasing the urgency for patching.
• CISA KEV Designation: The Cybersecurity and Infrastructure Security Agency (CISA) has added this vulnerability to its Known Exploited Vulnerabilities (KEV) catalog and CISA has warned of the vulnerability, calling for immediate and necessary measures. This requires U.S. federal civilian agencies to remediate this vulnerability by a specified date, indicating its serious and widespread risk.
• Zimbra Classic Interface Target: The vulnerability specifically targets the classic webmail interface. Organizations that still utilize the classic interface for Zimbra are at higher risk and should consider migrating users to a more secure interface (if available) or prioritizing patching.

Mitigation Strategies

• Apply the Patch Immediately: The most critical action is to apply the official patch provided by Zimbra to address CVE-2024-27443. Prioritize patching systems that are accessible from the internet.
• Disable the Classic Interface: If possible, disable or deprecate the Zimbra classic interface and migrate users to the modern UI. This will eliminate the attack vector and prevent exploitation.
• Implement Email Filtering: Employ email filtering rules to detect and block emails with suspicious calendar headers. Look for common XSS patterns and unusual characters in the header fields.
• User Awareness Training: Conduct user awareness training to educate employees about the risks of clicking on links or opening attachments from unknown senders. Emphasize the importance of verifying the authenticity of emails, especially those containing calendar invites.

Additional Information

If users have additional queries regarding this incident, they can use the 'Ask to Analyst' feature, contact SOCRadar directly, or open a support ticket for more information if necessary.