Detect SmarterMail Missing Authentication for Critical Function (CVE-2026-24423) in Microsoft Sentinel
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
KQL Detection Query
union isfuzzy=true
(
W3CIISLog
| where csUriStem has_any ("/api/", "/admin/", "/settings/", "/interface/", "/services/")
| where csMethod in ("POST", "PUT", "DELETE", "PATCH")
| where isempty(csUsername) or csUsername == "-"
| where scStatus in (200, 201, 204, 302)
| extend AuthBypass = true
),
(
AzureDiagnostics
| where ResourceType == "APPLICATIONGATEWAYS"
| where requestUri_s has_any ("/api/", "/admin/", "/settings/", "/interface/")
| where httpMethod_s in ("POST", "PUT", "DELETE")
| where userAgent_s !has "Mozilla" or isempty(userAgent_s)
)
| extend SmarterMailServer = Computer
| project TimeGenerated, SmarterMailServer, csClientIP, csUriStem, csMethod, scStatus, csUsername, csUserAgent
| where TimeGenerated > ago(1h)Detects unauthenticated HTTP requests to SmarterMail critical API and administrative endpoints. Focuses on state-changing methods (POST/PUT/DELETE) with missing or null authentication context returning success status codes.
Data Sources
Required Tables
False Positives & Tuning
- Health check services or monitoring tools polling SmarterMail endpoints without authentication headers
- Internal automation scripts that access SmarterMail APIs using service accounts that may log differently
- Misconfigured reverse proxies that strip authentication headers before forwarding to SmarterMail
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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