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CVE-2025-66376 is a stored cross-site scripting vulnerability in the Classic UI of Zimbra Collaboration Suite. It affects Zimbra Collaboration 10.0 before 10.0.18 and 10.1 before 10.1.13. The flaw is caused by improper neutralization and sanitization of attacker-controlled HTML and CSS content in email messages, specifically involving CSS @import directives. Crafted HTML email content can survive the client-side sanitization process and be reconstructed by the browser when the message is rendered in the Classic UI, resulting in execution of attacker-supplied JavaScript within the victim’s authenticated webmail session. Exploitation is view-based: opening or previewing a malicious email in the vulnerable Classic UI is sufficient to trigger script execution, without requiring the victim to click a link or open an attachment. The vulnerability was exploited in the wild as a zero-day prior to the release of fixes.
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An XSS vulnerability in Zimbra email servers previously exploited by TA488 in an earlier campaign using ZimReaper to steal emails, passwords, application passcodes, and two-factor authentication codes.
A Zimbra Collaboration vulnerability listed among vulnerabilities actively exploited or operationally weaponized in July 2026.
A vulnerability abused by threat actor CL-STA-1114.
A cross-site scripting vulnerability in the client-side HTML sanitizer of Zimbra Collaboration Suite that can be triggered via a half-click exploit when a victim opens or previews a malicious email, enabling malicious JavaScript execution.
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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.
Community discussion across Reddit, Mastodon, and other social sources.