CVE-2025-27915
Actively exploited. CVE-2025-27915 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2025-10-07) — exploitation has been observed in the wild, and US federal agencies are required to remediate it under BOD 22-01. Treat patching as urgent.
Public exploit code is available. Proof-of-concept or working exploit code for CVE-2025-27915 is indexed in Nuclei. Expect opportunistic scanning and exploitation attempts — prioritize remediation.
Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability that 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.
CSIRTS triage
- What
- Zimbra Collaboration Suite contains a cross-site scripting vulnerability due to insufficient sanitization of HTML content in ICS files.
- Who is affected
- Users of the Classic Web Client in Zimbra Collaboration Suite.
- Urgency
- Immediate action is required due to active exploitation and critical severity.
- Action
- Apply the latest security updates for Zimbra Collaboration Suite.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Exploitation confirmedAlready exploited in the wild (CISA KEV) — the prediction phase is over. Patch now. Riskier than 90% of all EPSS-scored CVEs.
Exploit availability
Public exploit or proof-of-concept code for CVE-2025-27915 is indexed in these free datasets. Available exploit code raises real-world risk independent of the CVSS score.
- NucleiA nuclei-templates detection/PoC template exists for this CVE.look it up ↗
Advisory coverage (1)
- criticalexploitedCVE-2025-27915: Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerabilitycisa-kev · 2025-10-07
External references
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