CVE-2025-48700
Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
Synacor Zimbra Collaboration Suite (ZCS)
An issue was discovered in Zimbra Collaboration (ZCS) 8.8.15 and 9.0 and 10.0 and 10.1. A Cross-Site Scripting (XSS) vulnerability in the Zimbra Classic UI allows attackers to execute arbitrary JavaScript within the user's session, potentially leading to unauthorized access to sensitive information. This issue arises from insufficient sanitization of HTML content, specifically involving crafted tag structures and attribute values that include an @import directive and other script injection vectors. The vulnerability is triggered when a user views a crafted e-mail message in the Classic UI, requiring no additional user interaction.
Exploitation status
CISA Known Exploited Vulnerabilities
Listed by CISA on 20 April 2026. US federal agencies were required to remediate it by 23 April 2026.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 1.7%, which is higher than 76.7% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Frequently asked questions
Is CVE-2025-48700 being exploited by ransomware groups?
No ransomware group in this database is currently recorded as exploiting CVE-2025-48700.
What does CVE-2025-48700 affect?
CVE-2025-48700 affects Synacor Zimbra Collaboration Suite (ZCS). An issue was discovered in Zimbra Collaboration (ZCS) 8.8.15 and 9.0 and 10.0 and 10.1. A Cross-Site Scripting (XSS) vulnerability in the Zimbra Classic UI allows attackers to execute arbitrary JavaScript within the user's session, potentially leading to unauthorized access to sensitive information. This issue arises from insufficient sanitization of HTML content, specifically involving crafted tag structures and attribute values that include an @import directive and other script injection vectors. The vulnerability is triggered when a user views a crafted e-mail message in the Classic UI, requiring no additional user interaction.
How severe is CVE-2025-48700?
CVE-2025-48700 is rated MEDIUM with a CVSS base score of 6.1. EPSS puts the probability of exploitation in the next 30 days at 1.7%, higher than 76.7% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 23 April 2026.
How should organisations respond to CVE-2025-48700?
Apply the vendor patch for Synacor Zimbra Collaboration Suite (ZCS) as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.