Detect SmarterMail Missing Authentication for Critical Function (CVE-2026-24423) in Splunk
Detects exploitation of CVE-2026-24423, a missing authentication vulnerability (CWE-306) in SmarterTools SmarterMail. This KEV-listed vulnerability allows unauthenticated attackers to access critical functions in SmarterMail, potentially enabling unauthorized administrative access, data exfiltration, or further lateral movement. Detection focuses on unauthenticated access patterns to administrative and critical API endpoints.
MITRE ATT&CK
SPL Detection Query
index=web OR index=iis sourcetype=iis OR sourcetype=ms:iis:auto
| search (uri_path="*/api/*" OR uri_path="*/admin/*" OR uri_path="*/settings/*" OR uri_path="*/interface/*" OR uri_path="*/services/*")
| search (method=POST OR method=PUT OR method=DELETE OR method=PATCH)
| search (status=200 OR status=201 OR status=204 OR status=302)
| where isnull(cs_username) OR cs_username="-" OR cs_username=""
| eval auth_bypass=if(isnull(cs_username) OR cs_username="-", "true", "false")
| stats count as request_count, values(uri_path) as endpoints, values(status) as status_codes, dc(c_ip) as unique_ips by cs_ip, _time
| where request_count > 1
| sort -request_count
| rename cs_ip as source_ipDetects unauthenticated access to SmarterMail administrative and API endpoints in IIS logs. Aggregates suspicious unauthenticated requests that result in success HTTP responses.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Automated monitoring or synthetic transaction tools that make unauthenticated health checks to SmarterMail
- Internal network scanners or vulnerability assessment tools running against the SmarterMail server
- Misconfigured load balancers stripping Authorization headers before reaching the IIS layer
Other platforms for CVE-2026-24423
Testing Methodology
Validate this detection against 3 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 1Unauthenticated GET to SmarterMail Admin API Endpoint
Expected signal: IIS access log entry with csUsername='-', cs-method=GET, sc-status=200, cs-uri-stem=/api/v1/settings/sysadmin/general
- Test 2Unauthenticated POST to SmarterMail User Creation Endpoint
Expected signal: IIS log: csMethod=POST, csUriStem=/api/v1/settings/sysadmin/users, csUsername=-, scStatus=200 or 201. SmarterMail app log: new user creation event for [email protected]
- Test 3Unauthenticated SmarterMail Mail Forwarding Rule Injection
Expected signal: IIS log entry: POST to /api/v1/settings/sysadmin/users/[email protected]/forwardingRules with csUsername='-' and scStatus=200. SmarterMail audit log: forwarding rule added for [email protected] pointing to external domain.
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