Security researchers have discovered that hackers exploited a zero-day vulnerability in Zimbra Collaboration Suite (ZCS) earlier this year using malicious calendar attachments to steal sensitive data. The attackers embedded harmful JavaScript code inside .ICS files—typically used to schedule and share calendar events—to target vulnerable Zimbra systems and execute commands within user sessions.
The flaw, identified as CVE-2025-27915, affected ZCS versions 9.0, 10.0, and 10.1. It stemmed from inadequate sanitization of HTML content in calendar files, allowing cybercriminals to inject arbitrary JavaScript code. Once executed, the code could redirect emails, steal credentials, and access confidential user information. Zimbra patched the issue on January 27 through updates (ZCS 9.0.0 P44, 10.0.13, and 10.1.5), but at that time, the company did not confirm any active attacks.
StrikeReady, a cybersecurity firm specializing in AI-based threat management, detected the campaign while monitoring unusually large .ICS files containing embedded JavaScript. Their investigation revealed that the attacks began in early January, predating the official patch release. In one notable instance, the attackers impersonated the Libyan Navy’s Office of Protocol and sent a malicious email targeting a Brazilian military organization. The attached .ICS file included Base64-obfuscated JavaScript designed to compromise Zimbra Webmail and extract sensitive data.
This article has been indexed from CySecurity News – Latest Information Security and Hacking Incidents
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