Actively exploited in the wild
Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability
Synacor - Zimbra Collaboration Suite (ZCS) · Listed in the CISA KEV since 2025-05-19. This indicates confirmed attacks in production environments.
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.
CVE-2024-27443
MediumCVSS 6.1KEVSummary
A Cross-Site Scripting (XSS) vulnerability exists in the CalendarInvite feature of the Zimbra webmail classic user interface in Zimbra Collaboration (ZCS) 9.0 and 10.0. An attacker can send an email with a crafted calendar header containing an XSS payload, which executes in the victim's session.
Risk Assessment
This could lead to execution of arbitrary JavaScript in the user's session, potentially resulting in session data theft or other actions on behalf of the victim.
Recommendation
Update Zimbra Collaboration to the latest version that fixes this vulnerability, and consider disabling the classic webmail interface until patched.
Other vulnerabilities in Zimbra Collaboration
See all- CVE-2016-4019High
Unspecified vulnerability in Zimbra Collaboration before version 8.7.0 allows remote attackers to affect integrity via unknown vectors.
- CVE-2016-3413High
Unspecified vulnerability in Zimbra Collaboration before 8.7.0 allows remote attackers to affect integrity via unknown vectors.
- CVE-2016-3406High
Multiple cross-site request forgery (CSRF) vulnerabilities in Zimbra Collaboration before version 8.7.0 allow remote attackers to hijack the authentication of unspecified victims via vectors involving the Client uploader extension or extension REST handlers.
- CVE-2016-3405High
Multiple unspecified vulnerabilities in Zimbra Collaboration before version 8.7.0 allow remote attackers to affect integrity.
- CVE-2016-3404High
Unspecified vulnerability in Zimbra Collaboration before 8.7.0 allows remote attackers to affect integrity via unknown vectors.
- CVE-2016-3402High
Unspecified vulnerability in Zimbra Collaboration before version 8.7.0 allows remote attackers to affect confidentiality via unknown vectors.
- CVE-2026-73570HighActively exploited
A remote code execution vulnerability exists in Zimbra Collaboration (ZCS) before 10.1.20 when the optional zimbra-snmp package is installed and SNMP notifications are enabled. Due to improper sanitization of untrusted input during SNMP notification processing, an unauthenticated attacker can send specially crafted SMTP requests that may result in execution of arbitrary operating system commands as the Zimbra user.
- CVE-2025-68645HighActively exploited
A Local File Inclusion (LFI) vulnerability exists in the Webmail Classic UI of Zimbra Collaboration (ZCS) 10.0 and 10.1 due to improper handling of user-supplied request parameters in the RestFilter servlet. An unauthenticated remote attacker can craft requests to the /h/rest endpoint to influence internal request dispatching, allowing inclusion of arbitrary files from the WebRoot directory.
- CVE-2025-48700MediumActively exploited
A Cross-Site Scripting (XSS) vulnerability in the Zimbra Classic UI allows attackers to execute arbitrary JavaScript within the user's session. It arises from insufficient sanitization of HTML content, including crafted tag structures and attribute values with an @import directive. The vulnerability triggers when a user views a crafted email in the Classic UI, requiring no additional interaction.
- CVE-2025-27915MediumActively exploited
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.
Original NVD description (English source)
An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0. A Cross-Site Scripting (XSS) vulnerability exists in the CalendarInvite feature of the Zimbra webmail classic user interface, because of improper input validation in the handling of the calendar header. An attacker can exploit this via an email message containing a crafted calendar header with an embedded XSS payload. When a victim views this message in the Zimbra webmail classic interface, the payload is executed in the context of the victim's session, potentially leading to execution of arbitrary JavaScript code.