Detect Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Exploitation in CrowdStrike LogScale
Detects exploitation attempts targeting CVE-2025-66376, a cross-site scripting vulnerability in Synacor Zimbra Collaboration Suite (ZCS). This KEV-listed vulnerability allows attackers to inject malicious scripts into the Zimbra web interface, potentially leading to session hijacking, credential theft, or further compromise of email infrastructure. Active exploitation has been confirmed by CISA.
MITRE ATT&CK
LogScale Detection Query
#event_simpleName=NetworkReceiveAccept OR #event_simpleName=NetworkConnectIP4 OR #event_simpleName=HttpRequest
| filter (
RemotePort in (80, 443, 8080, 8443)
AND (
HttpURI contains "/zimbra/"
OR HttpURI contains "/service/home/"
OR HttpURI contains "/service/soap/"
)
AND (
HttpURI contains "<script"
OR HttpURI contains "javascript:"
OR HttpURI contains "onerror="
OR HttpURI contains "onload="
OR HttpURI contains "onfocus="
OR HttpURI contains "eval("
OR HttpURI contains "document.cookie"
OR HttpURI contains "<svg"
OR HttpURI contains "<img"
)
)
| groupBy([aid, LocalAddressIP4, RemoteAddressIP4, HttpURI, HttpMethod, UserAgent], function=count(1, as=attempt_count))
| sort(attempt_count, order=desc)
| limit 500CrowdStrike Falcon LogScale (CQL) query detecting network events and HTTP requests from Zimbra-facing hosts or proxies where XSS payload patterns appear in URI parameters. Useful for host-based telemetry on mail servers running Zimbra.
Data Sources
Required Tables
False Positives & Tuning
- Vulnerability management platforms performing continuous web application scanning
- Legitimate Zimbra connector traffic with HTML-encoded content in URI parameters
- Authorized red team operations targeting email infrastructure
- Email archive or compliance tools that proxy and log Zimbra HTTP traffic
Other platforms for CVE-2025-66376
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Basic Reflected XSS Probe Against Zimbra Login
Expected signal: HTTP request to /zimbra/h/search with '<script>' in query parameter visible in web server access logs and WAF logs. Response code 200 or 302 depending on authentication state.
- Test 2Event Handler XSS Payload via Zimbra Mail Search
Expected signal: HTTP GET request with URL-encoded onerror= payload in query string visible in Zimbra access logs. Source IP and full URI captured in web server logs.
- Test 3SVG-Based XSS Payload Injection via Zimbra SOAP API
Expected signal: HTTP POST to /service/soap/ with SVG onload payload in request body. Body content inspection required — perimeter WAF or SIEM HTTP body logging must be enabled to capture this variant.
- Test 4JavaScript URI Scheme XSS in Zimbra Contact Import
Expected signal: HTTP POST to /service/home/ with multipart form data containing vCard. File upload logged in Zimbra access and mailbox logs. The javascript: URI in vCard URL field tests stored XSS if imported contact is rendered without sanitization.
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