Is CVE-2025-66376 actively exploited?

Yes. CVE-2025-66376 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, which means exploitation in the wild has been confirmed.

Can CVE-2025-66376 be exploited remotely?

The attack vector of CVE-2025-66376 has not been classified yet.

What is the CVSS score of CVE-2025-66376?

CVE-2025-66376 has not received a CVSS score yet.

HOME VULNERABILITIESCVE-2025-66376

UNKNOWNCISA KEVIN THE WILD

CVE-2025-66376

Published: April 11, 2026

Official Description

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.

NVD Source

Technical Analysis

CVE-2025-66376 requires local access, meaning attackers must already have a foothold on the target system.

Exploitation requires some privileges, which limits the exposure to scenarios where an attacker has already gained initial access.

CISA has added CVE-2025-66376 to the Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. U.S. federal agencies are required to patch this within the mandated timeframe, and all organizations should treat remediation as urgent.

Exploit & PoC Resources

ACTIVE EXPLOITATIONConfirmed exploitation in the wild

Exploit-DB

Offensive Security exploit database

GitHub PoC Search

Community PoC repositories

Rapid7 / Metasploit

Metasploit module search

PacketStorm

Security advisories & exploits

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News & Research Mentioning CVE-2025-66376

CISA Warns of Zimbra, SharePoint Flaw Exploits; Cisco Zero-Day Hit in Ransomware Attacks

The Hacker News· Mar 19, 2026

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has urged government agencies to apply patches for two security flaws impacting Synacor Zimbra Collaboration Suite (ZCS) and Microsoft Office SharePoint, stating they have been actively exploited in the wild. The vulnerabilities in question are as follows - CVE-2025-66376 (CVSS score: 7.2) - A stored cross-site scripting [xlite_meta score:68 src:The Hacker News xlite_fp:6ff1ea13fac51ab574bdb79aca3e527948acfdce0dcf1a9ec8eeba506076f075]

CISA Adds One Known Exploited Vulnerability to Catalog

CISA Alerts· Mar 18, 2026

CISA has added one new vulnerability to its Known Exploited Vulnerabilities (KEV) Catalog, based on evidence of active exploitation. CVE-2025-66376 Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability This type of vulnerability is a frequent attack vector for malicious cyber actors and poses significant risks to the federal enterprise. Binding Operational Directive (BOD) 22-01: Reducing the Significant Risk of Known Exploited Vulnerabilities established the KEV Catalog as a living list of known Common Vulnerabilities and Exposures (CVEs) that carry significant risk to the federal enterprise. BOD 22-01 requires Federal Civilian Executive Branch (FCEB) agencies to remediate identified vulnerabilities by the due date to protect FC [xlite_meta score:48 src:CISA Alerts xlite_fp:82b85b7ac0d35e60b58b7a17426b47fe3020b124789936e4802ab94f74950fee]