CVE-2025-27915 — zm-build
MEDIUMCVE-2025-27915 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability. It is in CISA's Known Exploited Vulnerabilities catalog (added 2025-10-07) — treat it as actively exploited and patch now. A fix is available — see the affected versions and patch details below.
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2025-10-07. Federal agencies were required to remediate by 2025-10-28.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2025-27915.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2025-27915 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 394,415 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Description
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.
Affected Products
zimbra collaboration suitesynacorDetection & mitigation playbook
VulnerabilityDetect
Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).
Fix
Upgrade the affected component to the fixed release for CVE-2025-27915, or apply your distribution's backported patch — distro builds are often patched at an older version number, so check your vendor's advisory rather than the upstream version alone.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
How to detect CVE-2025-27915
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2025-27915 -u https://target- Template
- Zimbra - Cross-Site Scripting via ICS Files
- Severity
- medium
- Impact
- Authenticated users viewing malicious ICS files can have JavaScript executed in their browser context through stored XSS, potentially leading to session hijacking and data exfiltration.
- Remediation
- Upgrade to Zimbra Collaboration Suite version 9.0.1, 10.0.13, or 10.1.5 or later that properly sanitizes HTML content in ICS files.
Template by ProjectDiscovery nuclei-templates (Snbig, EhsanCreator, eliotworkspac-max), MIT licensed. View the full template. Scan only systems you are authorised to test.
Frequently Asked Questions
Is CVE-2025-27915 in your dependencies?
Find it across , including transitive dependencies.