Detect Synacor Zimbra Collaboration Suite PHP Remote File Inclusion (CVE-2025-68645) in Splunk
Detects exploitation of CVE-2025-68645, a PHP Remote File Inclusion (RFI) vulnerability in Synacor Zimbra Collaboration Suite (ZCS). CWE-98 class vulnerabilities allow attackers to inject and execute remote PHP files via unsanitized user-controlled input passed to PHP file inclusion functions, enabling arbitrary code execution in the context of the web server process. This vulnerability is listed in the CISA Known Exploited Vulnerabilities catalog.
MITRE ATT&CK
- Tactic
- Initial Access Execution Persistence
SPL Detection Query
index=web OR index=os sourcetype IN ("zimbra_access", "zimbra_mailbox", "linux_secure", "syslog")
| eval is_rfi_url=if(match(uri_query, "(?i)(=https?://|=ftp://|=file://|=php://input)"), 1, 0)
| eval is_rfi_cmd=if(match(process, "(?i)(include|require|include_once|require_once).{0,50}https?://"), 1, 0)
| eval is_suspicious_write=if(match(file_path, "/opt/zimbra/(data/tmp|store|index)/.*\.php$"), 1, 0)
| eval is_outbound_fetch=if(match(process, "(?i)(curl|wget|python.*urllib|python.*requests).*http"), 1, 0)
| where is_rfi_url=1 OR is_rfi_cmd=1 OR is_suspicious_write=1 OR is_outbound_fetch=1
| eval zimbra_host=if(match(host, "zimbra") OR match(dest, "zimbra"), 1, 0)
| where zimbra_host=1 OR match(file_path, "/opt/zimbra")
| stats count by _time, host, src_ip, dest_ip, uri_path, uri_query, process, file_path, user
| sort -_timeIdentifies RFI exploitation patterns in Zimbra ZCS by searching for URL-based include parameters in web logs and suspicious PHP file creation activity in Zimbra data paths.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Legitimate IMAP/SMTP proxy configuration referencing remote URIs in Zimbra admin interface
- Zimlet installation processes that temporarily fetch remote PHP archives
- Third-party Zimbra integrations using webhook callbacks that include URL parameters
- Automated Zimbra health check scripts that make outbound HTTP requests
Other platforms for CVE-2025-68645
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 1Simulate PHP RFI via HTTP Request Parameter Injection
Expected signal: Web server access log entry with URL parameter containing http://attacker.lab/malicious.php; network connection attempt from PHP process to attacker.lab:80
- Test 2Create Simulated Web Shell in Zimbra Data Directory
Expected signal: File creation event for /opt/zimbra/data/tmp/lab_test/shell_test_atomic.php; auditd syscall event for open/write by test user
- Test 3PHP Process Invoking Remote File Fetch (RFI Simulation)
Expected signal: Process telemetry showing php binary with command-line containing http:// URL; network connection attempt from php process to 127.0.0.1:9999 (or external IP in real attack)
- Test 4Zimbra Config File Access by Non-Zimbra Process (Post-Exploitation Credential Harvest)
Expected signal: Auditd open/read syscall event on /opt/zimbra/conf/localconfig.xml by non-zimbra UID; file access timestamp update visible in stat output
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Get the full detection package for CVE-2025-68645 including response playbook, investigation guide, and atomic red team tests.