HIGH CVSS 7.2
Published: 2026-01-05

CVE-2025-66376

synacor zimbra_collaboration_suite Security Advisory (CVE-2025-66376)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2025-66376 impacting synacor zimbra_collaboration_suite. Evaluated with CVSS Base Score of 7.2 (HIGH).

Original NVD Description

Source: NIST NVD
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.

📊 CVSS v3.1 Metric Breakdown

Attack Vector
Network (AV:N)
Exploitable remotely across internet boundaries
Attack Complexity
Low (AC:L)
No specialized conditions required
Privileges Required
None (PR:N)
Unauthenticated execution
User Interaction
None (UI:N)
Zero human interaction required
Scope
Changed (S:C)
Impacts components beyond caller authority
Confidentiality
Low (C:L)
Partial information leakage
Integrity
Low (I:L)
Partial data modification possible
Availability
None (A:N)
No system availability impact

🎯 Affected Versions Matrix

Affected Product synacor / zimbra_collaboration_suite
Affected Versions *
Weakness Enumeration CWE-79

Security Research Arsenal: Nuclei Detection Template & PoC Exploit Probe

High-Intent Research Tool

Ready-to-use security scanner signatures, active verification probe skeletons, and remediation playbooks for CVE-2025-66376 impacting synacor zimbra_collaboration_suite.

⚡ Nuclei Detection Template (YAML) cve-2025-66376.yaml
id: cve-2025-66376

info:
  name: synacor zimbra_collaboration_suite - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: high
  description: |
    Automated signature & scanner for CVE-2025-66376 affecting synacor zimbra_collaboration_suite.
    Evaluation: 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 ...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2025-66376
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
    cvss-score: 7.2
    cve-id: CVE-2025-66376
    cwe-id: CWE-79
  tags: cve,cve-2025-66376,synacor,zimbra_collaboration_suit,high

http:
  - method: GET
    path:
      - "{BaseURL}/"
      - "{BaseURL}/api/"
    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        words:
          - "zimbra_collaboration_suite"
        part: body
🐍 PoC Exploit & Verification Probe (Python 3) poc_cve-2025-66376.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2025-66376
# Target: synacor zimbra_collaboration_suite | CVSS: 7.2 (HIGH)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2025-66376 (synacor zimbra_collaboration_suite)...")
    headers = {
        "User-Agent": "CyberVault-Audit-Scanner/2.0",
        "Accept": "*/*"
    }
    try:
        r = requests.get(f"{target_url.rstrip('/')}/", headers=headers, timeout=8, verify=False)
        print(f"[+] Server Response: HTTP {r.status_code} | Server Banner: {r.headers.get('Server', 'Unknown')}")
        if r.status_code < 500:
            print(f"[!] Target reachable. Verify version against synacor zimbra_collaboration_suite scope (*).")
        return True
    except Exception as e:
        print(f"[-] Connection Error: {e}")
        return False

if __name__ == '__main__':
    url = sys.argv[1] if len(sys.argv) > 1 else "http://localhost:8080"
    verify_vulnerability(url)
🛡️ Quick Patch & Remediation Script (Bash) patch_cve-2025-66376.sh
# Recommended Remediation & Patching Commands for CVE-2025-66376
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install zimbra_collaboration_suit 2>/dev/null || \
sudo dnf upgrade zimbra_collaboration_suit 2>/dev/null || \
sudo yum update zimbra_collaboration_suit

# 2. Inspect installed package versions for vulnerable scope:
dpkg -l | grep -i zimbra_collaboration_suit 2>/dev/null || rpm -qa | grep -i zimbra_collaboration_suit

# 3. Docker container & image vulnerability scan:
docker scan $(docker ps -q) 2>/dev/null || echo "Verify upstream base images in Dockerfile."

🛡️ Remediation & Security Action

  • Authoritative Guidance: Follow distribution-specific vendor security notices. Advisory status and package patches vary by distribution release.
  • Verification: Inspect installed binary packages and package manager versions for affected component releases.
  • Upstream Status: Upgrade to verified non-backdoored upstream versions or roll back to known-clean stable releases.
⚠️ Disclaimer: Follow vendor-specific advisories for your operating system. CyberVault does not fabricate unsupported remediation scripts.

❓ Frequently Asked Questions (FAQ) & Remediation Guide

How do I fix CVE-2025-66376 in synacor zimbra_collaboration_suite?

Review vendor-specific security notices and update synacor zimbra_collaboration_suite packages to the latest patched release immediately. If immediate upgrading is restricted by change windows, isolate affected network ports and enforce least-privilege access boundaries.

Is there an active exploit or public PoC for CVE-2025-66376?

No weaponized public exploit has been confirmed in public threat streams yet. Continuous surveillance is active across GitHub and security feeds.

What is the CVSS 3.1 severity rating and impact for CVE-2025-66376?

CVE-2025-66376 is classified with a CVSS 3.1 Base Score of 7.2 (HIGH). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
7.2
HIGH SEVERITY
CVE ID CVE-2025-66376
Weakness CWE-79
Vendor synacor
Product zimbra_collaboration_suite
Published 2026-01-05
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N