What is CVE-2025-27915?
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 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.
The record classifies CVE-2025-27915 under weakness class CWE-79. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs a user to take an action first. 30 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 572 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 5.4 — MEDIUM
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N - EPSS (FIRST)
- 3.9% probability of exploitation in the next 30 days, higher than 90.1% of all scored CVEs
- CISA KEV
- Listed since 2025-10-07, federal remediation deadline 2025-10-28
- Threadlinqs priority
- 9/10 — CISA KEV-listed, which Threadlinqs floors at 9
- Published
- 2025-03-12, last modified 2026-02-26
Is CVE-2025-27915 being exploited?
CISA added CVE-2025-27915 to the Known Exploited Vulnerabilities catalog on 2025-10-07, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2025-10-28 under BOD 22-01. Weaponised exploit code for CVE-2025-27915 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. A ProjectDiscovery Nuclei detection template exists (http/cves/2025/CVE-2025-27915.yaml). It currently carries a trending score of 43 in the Threadlinqs vulnerability feed.
- trickest/cve (trickest)
Affected products and versions
- Synacor: Zimbra Collaboration Suite, Zimbra Collaboration Suite 9.0.0
Showing 2 of 30 recorded product entries.
How to fix CVE-2025-27915
Because CVE-2025-27915 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2025-10-28. No vendor patch reference has been recorded for CVE-2025-27915 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.
Threat activity tracking CVE-2025-27915
1 tracked threat in the Threadlinqs corpus references CVE-2025-27915, either in the campaign’s CVE list or as an indicator on the campaign record.
Sources
Enriched from CVE.org, NVD, FIRST EPSS, CISA KEV, GitHub Security Advisories, public proof-of-concept repositories, ProjectDiscovery Nuclei. Last verified by Threadlinqs on . This product uses the NVD API but is not endorsed or certified by the NVD.