Stored XSS in Zimbra Collaboration Classic UI via CSS @import in HTML email
CVE-2025-66376 is a stored cross-site scripting vulnerability in Zimbra Collaboration (ZCS) Classic UI affecting 10.0 before 10.0.18 and 10.1 before 10.1.13. The flaw can be triggered by a remote unauthenticated attacker sending a specially crafted HTML email that abuses Cascading Style Sheets (CSS) @import directives. When the message is viewed in the Zimbra Classic web interface, attacker-controlled script executes in the context of the victim’s authenticated browser session. Reporting indicates the issue resides in how malicious HTML/CSS content in email is handled in the Classic UI, and vendor remediation included upgrading the AntiSamy library to 1.7.8 and removing outdated risky code.
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Exploits
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Recent activity
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A Zimbra XSS vulnerability that was exploited by APT28 in phishing attacks against Ukrainian government-related targets via malicious emails opened in vulnerable Zimbra webmail sessions.
A high-severity stored cross-site scripting vulnerability in Zimbra Collaboration that has been exploited in intrusions targeting Ukraine.
A high-severity stored cross-site scripting vulnerability in Zimbra Collaboration that was weaponized in Ukraine-targeted intrusions.
A high-severity stored cross-site scripting vulnerability in Zimbra Collaboration that was reportedly weaponized in Ukraine-targeted intrusions.
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Every observed campaign linking this CVE to a named adversary.
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Cross-references every affected SKU, including bundled OEM variants.
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