Detect Zimbra Collaboration Suite XSS Exploitation (CVE-2025-48700) in Google Chronicle
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
YARA-L Detection Query
rule zimbra_xss_cve_2025_48700 {
meta:
author = "df00tech Detection Engineering"
description = "Detects XSS exploitation attempts against Zimbra Collaboration Suite (CVE-2025-48700)"
severity = "HIGH"
priority = "HIGH"
reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-48700"
cve = "CVE-2025-48700"
yara_version = "YL2.0"
rule_version = "1.0"
events:
$e.metadata.event_type = "NETWORK_HTTP"
(
re.regex($e.network.http.request_url, `(?i)(/zimbra/|/service/soap|/h/|/m/)`)
or re.regex($e.target.hostname, `(?i)(zimbra|webmail)`)
)
(
re.regex($e.network.http.request_url, `(?i)(<script|javascript:|onerror=|onload=|eval\(|document\.cookie|document\.location|String\.fromCharCode|atob\()`)
or re.regex($e.network.http.request_url, `(%3Cscript|%6A%61%76%61%73%63%72%69%70%74|&#[xX]3[cC])`)
or re.regex($e.network.http.referral_url, `(?i)(<script|javascript:|onerror=|onload=)`)
)
$e.network.http.response_code in (200, 301, 302, 400)
match:
$e.principal.ip over 10m
outcome:
$risk_score = max(
if($e.network.http.response_code = 200, 80, 50)
)
$xss_payloads = array_distinct($e.network.http.request_url)
$target_hosts = array_distinct($e.target.hostname)
$source_ips = array_distinct($e.principal.ip)
condition:
#e >= 1
}Chronicle YARA-L 2.0 rule that detects XSS payload patterns in HTTP requests targeting Zimbra URL paths, matching both raw and URL-encoded XSS variants in request URLs and referrer headers.
Data Sources
Required Tables
False Positives & Tuning
- Authorized red team exercises targeting Zimbra infrastructure that generate XSS payloads
- Email security gateway scanning that generates test XSS payloads in log entries
- Legitimate Zimbra admin operations involving HTML content in URL parameters
- Third-party integrations using Zimbra APIs that pass encoded data resembling XSS patterns
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
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