Detect Zimbra Collaboration Suite XSS Exploitation (CVE-2025-48700) in Elastic Security
Detects exploitation of a stored or reflected cross-site scripting (XSS) vulnerability in Synacor Zimbra Collaboration Suite (ZCS). This KEV-listed vulnerability allows attackers to inject malicious scripts into the Zimbra web client, potentially leading to session hijacking, credential theft, or further lateral movement within the organization. XSS in webmail platforms is frequently exploited by threat actors to steal session tokens and pivot to email account compromise.
MITRE ATT&CK
Elastic Detection Query
sequence by source.ip with maxspan=10m
[network where
url.path : ("/zimbra/*", "/service/soap*", "/h/*", "/m/*") and
(
url.query : ("*<script*", "*javascript:*", "*onerror=*", "*onload=*", "*eval(*", "*document.cookie*") or
url.query : ("*%3Cscript*", "*%6A%61%76%61%73%63%72%69%70%74*") or
http.request.referrer : ("*<script*", "*javascript:*", "*onerror=*")
) and
http.response.status_code in (200, 301, 302)
]
[network where
url.path : ("/zimbra/*", "/service/*") and
http.response.status_code == 200
]EQL sequence detection that identifies an XSS payload injection followed by a successful Zimbra request from the same source IP within 10 minutes, suggesting active exploitation with session manipulation.
Data Sources
Required Tables
False Positives & Tuning
- Security researchers or automated scanners probing Zimbra endpoints during authorized tests
- Encoded email attachments with HTML content that match XSS patterns in network captures
- Load balancer health checks that include special characters in request paths
- Browser extensions that modify requests and include script-like content in headers
Other platforms for CVE-2025-48700
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 via Zimbra Search Parameter
Expected signal: Web server access log entry showing GET /zimbra/h/search with q=%3Cscript%3E... URL-encoded payload, HTTP 200 response, source IP of test system
- Test 2Event Handler XSS Payload Delivery via Zimbra URL Parameter
Expected signal: Web server access log showing GET requests to /zimbra/h/compose and /zimbra/h/ with onerror= and onload= patterns in URI query strings, HTTP response codes
- Test 3Simulated Session Cookie Exfiltration via XSS in Zimbra (Post-Exploitation)
Expected signal: Outbound HTTP GET request from Zimbra user's source IP to external attacker-controlled IP containing URL-encoded session token data in the query string; proxy/firewall logs showing unusual outbound connection from Zimbra webmail user IP
- Test 4Stored XSS Payload Submission via Zimbra SOAP API
Expected signal: Zimbra nginx access log showing POST to /service/soap with HTTP 200 response; Zimbra mailbox.log showing CreateContactRequest SOAP operation; POST body (if logged) containing the HTML-encoded XSS payload in the notes field
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