Detect SmarterMail Authentication Bypass via Alternate Path or Channel (CVE-2026-23760) in CrowdStrike LogScale
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
LogScale Detection Query
#event_simpleName=NetworkReceiveAcceptIP4
| TargetPort in (80, 443, 8080, 8443, 25, 587, 993, 995)
| RemoteAddressIP4 != "127.0.0.1"
| join type=inner
[
#event_simpleName=ProcessRollup2
| ImageFileName matches regex "(?i)SmarterMail|MailService|smtpd"
| select aid, ContextProcessId, ImageFileName, CommandLine
]
key=[aid, TargetProcessId = ContextProcessId]
| stats count(RemoteAddressIP4) as connection_count, dc(TargetPort) as distinct_ports, values(ImageFileName) as mail_processes
by aid, RemoteAddressIP4, bin(timestamp, 5m)
| where connection_count > 20 or distinct_ports > 3
| join type=inner
[
#event_simpleName=DnsRequest
| DomainName matches regex "(?i)SmarterMail"
| select aid, DomainName
]
key=[aid]
| select timestamp, aid, RemoteAddressIP4, connection_count, distinct_ports, mail_processes, DomainNameCrowdStrike Falcon CQL query correlating process and network events to identify SmarterMail service handling an anomalously high number of inbound connections from a single remote IP, consistent with automated bypass exploitation.
Data Sources
Required Tables
False Positives & Tuning
- High-traffic mail servers receiving burst connections from bulk sender IPs
- Authorized mail relay or gateway appliances opening many connections to SmarterMail
- Backup or archival solutions that connect to the mail server repeatedly in short windows
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'
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Get the full detection package for CVE-2026-23760 including response playbook, investigation guide, and atomic red team tests.