Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import d
Affects Zimbra Collaboration 10.0 before 10.0.18 and 10.1 before 10.1.13, only in the Classic UI. CVSS rates it 7.2 (high). Fixed in 10.0.18 and 10.1.13.
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Listed in CISA KEV
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Actively exploited
- Fix
- Fixed in 10.0.18, 10.1.13
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
Zimbra Collaboration (ZCS) email and collaboration software, specifically its Classic web interface, is affected. An attacker can hide malicious script inside an HTML email using CSS @import directives, which may run in a user's browser when the message is viewed, potentially allowing theft of session data or actions performed on the user's behalf.
Summarized by anthropic/claude-haiku-5.5. Verify details against the original sources.
Read the original description
Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.
Timeline
- CVE published
- Added to CISA KEV
CISA has evidence of exploitation in the wild
- Record last updated
- CISA remediation deadline
Due date for US federal agencies to patch
- EPSS reached 10%
FIRST estimates at least a 10% chance of exploitation in the next 30 days
Affected versions
- Zimbra Collaboration
From 10.0 · fixed in 10.0.18; From 10.1 · fixed in 10.1.13
References 5
Questions about CVE-2025-66376
What does this mean?
The Classic UI fails to properly filter CSS @import directives in email HTML, so a stored script can be placed in a message and run in the browser of whoever views it. The flaw is stored, meaning the malicious content is saved on the server rather than requiring a crafted link.Source: wiki.zimbra.com
Am I affected, and how do I check?
Zimbra Collaboration (ZCS) versions 10.0 before 10.0.18 and 10.1 before 10.1.13 are in scope, and only when the Classic UI is used. To check, look at the installed ZCS version with the server version command and confirm which web interface users access.Source: wiki.zimbra.com
What should I do about it?
Upgrade to Zimbra Collaboration 10.0.18 or 10.1.13, or any later release in those branches. The fix is included in these versions.Source: wiki.zimbra.com
Is it being exploited?
Yes. CISA added it to its Known Exploited Vulnerabilities catalog on 2026-03-18, which means it has evidence of attacks. No public exploit code is tracked.Source: cisa.gov, cve.now feed data