Detect Zimbra Collaboration Suite XSS Exploitation (CVE-2025-48700) in Splunk
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
SPL Detection Query
index=web OR index=proxy OR index=zimbra sourcetype IN ("access_combined", "iis", "zimbra:access", "pan:traffic")
(uri_path IN ("/zimbra/*", "/service/soap*", "/h/*", "/m/*")
OR dest_host IN ("zimbra", "webmail", "mail"))
(
uri_query IN ("*<script*", "*javascript:*", "*onerror=*", "*onload=*", "*eval(*", "*document.cookie*", "*document.location*", "*String.fromCharCode*", "*atob(*")
OR http_referrer IN ("*<script*", "*javascript:*", "*onerror=*", "*onload=*")
OR uri IN ("*%3Cscript*", "*%6A%61%76%61%73%63%72%69%70%74*", "*<script*")
)
status IN (200, 301, 302, 400)
| eval xss_indicator=case(
match(uri_query, "(?i)<script"), "raw_script_tag",
match(uri_query, "(?i)javascript:"), "javascript_proto",
match(uri_query, "(?i)onerror|onload|onmouseover"), "event_handler",
match(uri_query, "(?i)document\.cookie"), "cookie_theft",
match(uri_query, "(?i)eval\\("), "eval_function",
1=1, "url_encoded_xss"
)
| stats
count AS request_count,
dc(uri_query) AS unique_payloads,
values(xss_indicator) AS indicators,
values(uri_query) AS sample_payloads,
min(_time) AS first_seen,
max(_time) AS last_seen
BY src_ip, http_user_name, dest_host, span(_time, 5m)
| where request_count >= 1
| eval cve="CVE-2025-48700", severity="high"Detects XSS exploitation attempts against Zimbra web endpoints by searching for common XSS payload patterns including script tags, javascript: protocol handlers, event handlers, and URL-encoded variants in access logs.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Authorized penetration testing or vulnerability scanning against Zimbra infrastructure
- Email content with HTML entities that get logged in web access logs
- Third-party integrations that pass encoded data through Zimbra URL parameters
- Security monitoring tools that replay captured XSS payloads for testing
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
Unlock Pro Content
Get the full detection package for CVE-2025-48700 including response playbook, investigation guide, and atomic red team tests.