# CVE-2025-27915 — Synacor Zimbra Collaboration Suite **CISA KEV** > As of 2026-02-26, CVE-2025-27915 is a MEDIUM-severity vulnerability in Synacor Zimbra Collaboration Suite, CVSS v3.1 5.4, EPSS 3.9% (90.1th percentile). It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2025-10-07), with a US federal remediation deadline of 2025-10-28. Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2025-27915, most recently “Operation RoundPress: TA458 Deploys SpyPress Malware via Half-Click Webmail Zero-Days (CVE-2025-27915, CVE-2025-3929, CVE-2026-8496)”. **Last updated:** 2026-02-26 ## 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](https://intel.threadlinqs.com/cwe/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](https://github.com/trickest/cve/blob/main/2025/CVE-2025-27915.md) (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. - [Operation RoundPress: TA458 Deploys SpyPress Malware via Half-Click Webmail Zero-Days (CVE-2025-27915, CVE-2025-3929, CVE-2026-8496)](https://intel.threadlinqs.com/threat/TL-2026-2579) — CRITICAL · 2026-07-23 ## 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 2026-09-28. This product uses the NVD API but is not endorsed or certified by the NVD. **Other references** - [wiki.zimbra.com](https://wiki.zimbra.com/wiki/Security_Center) - [wiki.zimbra.com (10.1)](https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.5#Security_Fixes) - [wiki.zimbra.com (10.0)](https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.13#Security_Fixes) - [wiki.zimbra.com (P44)](https://wiki.zimbra.com/wiki/Zimbra_Releases/9.0.0/P44#Security_Fixes) Canonical: https://intel.threadlinqs.com/cve/CVE-2025-27915 Full detection coverage and IOCs for threats exploiting CVE-2025-27915 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp