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CVE-2025-27915

Synacor — Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability

Synacor · CWE-79 — Cross-site scripting · in CISA KEV since 2025-10-07

KEV since 2025 · listed over a yearCISA KEVActively Exploited
75

EVRS 75 of 100 Urgent

Patch This Cycle

Rank 1,143 of 2,960 tracked

Raised to the floor for a confirmed exploited vulnerability.

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Why it scores 75

Evidence available: 6 of 7 signals

Listed in the CISA KEV catalog, and an EPSS probability of 0.041.

  • CISA KEVApplied
  • RansomwareDid not apply
  • Vendor exploitationDid not apply
  • EPSSApplied
  • Microsoft Exploitability IndexNot applicable
  • Pre-patch disclosureNo data
  • KEV recencyDid not apply
  • CVSSApplied

The band answers “how soon”, not “how bad”. No data for: Pre-patch disclosure. Why some signals show no data

Fix

Patch or fixed version identified

CISA required action

Fixed in

zimbra collaboration suite: update to 10.0.13 or later | zimbra collaboration suite: update to 10.1.5 or later

Affected versions

  • zimbra collaboration suite>= 10.0.0 < 10.0.13>= 10.1.0 < 10.1.59.0.0

Remediation

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Fixed versions from NVD.

Evidence

Each value with its source
MeasureValueSource
CVSS base scoreHow severe the flaw is in itself. It does not say how likely an attack is. 5.4 NVD
FIRST EPSSFIRST's estimate of the chance this is exploited in the next 30 days, and how that ranks against all CVEs. 0.041 (90.6th pctl) FIRST EPSS
Actively exploitedWhether a source of record has confirmed attacks using it in the wild. Confirmed CISA KEV
Ransomware campaign useWhether CISA has seen ransomware operators use it. Unknown or none CISA KEV
CISA remediation deadlineThe date US federal agencies must have fixed or mitigated it. 2025-10-28 · KEV since 2025 · listed over a year CISA KEV
Public exploit moduleA module existing is not the same as active exploitation. None known Metasploit
EUVD cross-referenceENISA's record: CVSS 5.4 (v3.1), assigned by mitre. Listed ENISA EUVD

Description

NVD

An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS files. When a user views an e-mail message containing a malicious ICS entry, its embedded JavaScript executes via an ontoggle event inside a <details> tag. This allows an attacker to run arbitrary JavaScript within the victim's session, potentially leading to unauthorized actions such as setting e-mail filters to redirect messages to an attacker-controlled address. As a result, an attacker can perform unauthorized actions on the victim's account, including e-mail redirection and data exfiltration.

What CISA says to do