Stored XSS in Zimbra Collaboration Classic Web Client via ICS files
CVE-2025-27915 is a stored cross-site scripting vulnerability in Zimbra Collaboration Suite (ZCS) affecting the Classic Web Client. The issue is caused by insufficient sanitization of HTML content embedded in iCalendar (.ICS) files. When a victim views an email message containing a malicious ICS entry, attacker-supplied JavaScript can execute in the context of the victim’s authenticated Zimbra webmail session, including via an ontoggle event inside a <details> tag. Reported affected versions include ZCS 9.0, 10.0, and 10.1, with vulnerable ranges described as 9.0.0 all patches, 10.0.x before 10.0.13, and 10.1.x before 10.1.5. Public reporting also states the flaw was exploited as a zero-day in targeted attacks using weaponized ICS attachments.
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Recent activity
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A CVE referenced only as an example template for extractor syntax; no vulnerability details are provided in the content.
A Zimbra XSS vulnerability exploited as a zero-day to execute arbitrary JavaScript and create malicious email filters that forward messages to attacker-controlled servers.
A stored XSS vulnerability in Zimbra Collaboration, allowing mailbox takeover via malicious ICS attachments.
A stored cross-site scripting (XSS) vulnerability in Zimbra Collaboration Suite Classic Web Client, triggered via ICS (iCalendar) files, with specific affected version ranges noted.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.