Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability in the Classic UI where attackers could abuse Cascading Style Sheets (CSS) @import directives in email HTML.
A remote attacker, without authentication, can achieve partial data exposure, partial data tampering. Federal agencies are required to remediate by 2026-04-01 under CISA BOD 22-01.
This is a Cross-Site Scripting (XSS) (CWE-79) vulnerability in Synacor Zimbra Collaboration Suite (ZCS). 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. Exploitation requires remote network access, low attack complexity, no authentication required, and no user interaction required.
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Phishing link
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Malicious file
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Server compromised
Probably yes if any of these apply:
CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2026-03-18 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2026-04-01.
Manual remediation steps
Apply the Vendor Patch
This vulnerability is in the CISA Known Exploited Vulnerabilities catalog — apply the vendor's security update as soon as possible.
CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
References
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References