Detect SmarterMail Authentication Bypass via Alternate Path or Channel (CVE-2026-23760) in Elastic Security
Detects exploitation of CVE-2026-23760, an authentication bypass vulnerability (CWE-288) in SmarterTools SmarterMail. Attackers can access protected functionality through an alternate path or channel without valid credentials, potentially leading to unauthorized mailbox access, data exfiltration, or lateral movement. This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog.
MITRE ATT&CK
- Tactic
- Initial Access Credential Access
Elastic Detection Query
sequence by source.ip with maxspan=5m
[network where event.dataset == "iis.access" and
url.path : ("/api/*", "/autodiscover/*", "/ews/*", "/mapi/*", "/webmail/*", "*/admin*", "*/config*") and
http.request.method in ("POST", "GET", "PUT") and
http.response.status_code in (200, 201, 302) and
(
url.query : ("*bypass*", "*token=*", "*auth=*", "*session=*") or
(not user_agent.original : "*Mozilla*" and url.path : "/api/*")
)
] with runs=5
| where #sequencesCount >= 3Uses EQL sequence detection to identify repeated suspicious requests to SmarterMail authentication endpoints from the same source IP within a short window, indicative of automated bypass exploitation.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate high-frequency API polling from authorized integration services
- Automated backup or archival tools accessing mailbox endpoints without browser headers
- Internal network scanners or health monitoring probes targeting mail server endpoints
Other platforms for CVE-2026-23760
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 1Probe SmarterMail Admin API Without Credentials
Expected signal: IIS access log entry showing GET /api/v1/settings/sysadmin/general with HTTP 200 or 302, source IP of test host, user-agent 'python-requests/2.28'
- Test 2Enumerate SmarterMail User Accounts via Bypass Path
Expected signal: IIS logs showing sequential requests to /api/v1/accounts, /autodiscover/autodiscover.xml, /ews/exchange.asmx with non-standard user-agent from a single IP within seconds
- Test 3SmarterMail Authentication Bypass via Token Parameter Injection
Expected signal: Windows Event Log network connection events and IIS access log entries showing GET requests with 'token=', 'auth=', 'session=' query parameters, HTTP responses 200/302/401, user-agent 'TestClient/1.0'
Unlock Pro Content
Get the full detection package for CVE-2026-23760 including response playbook, investigation guide, and atomic red team tests.