Detect SmarterMail Unrestricted File Upload Exploitation (CVE-2025-52691) in Microsoft Sentinel
Detects exploitation of CVE-2025-52691, an unrestricted file upload vulnerability in SmarterTools SmarterMail. This vulnerability allows attackers to upload files with dangerous types (e.g., web shells, executables) to the mail server, potentially enabling remote code execution. This CVE is listed in CISA's Known Exploited Vulnerabilities catalog.
MITRE ATT&CK
- Tactic
- Initial Access Execution Persistence
KQL Detection Query
union DeviceFileEvents, DeviceProcessEvents
| where TimeGenerated > ago(7d)
| where DeviceName has_any ("mail", "smartermail", "smtp")
| where (
(ActionType == "FileCreated" and FileName matches regex @"\.(aspx|asp|php|jsp|cfm|cgi|pl|py|rb|sh|exe|dll|bat|cmd|ps1|vbs|hta)$"
and FolderPath matches regex @"(?i)(smartermail|smarter\\mail|mailroot|webmail)")
or
(ActionType in ("ProcessCreated") and InitiatingProcessName =~ "SmarterMail.exe"
and FileName in~ ("cmd.exe", "powershell.exe", "wscript.exe", "cscript.exe", "mshta.exe", "certutil.exe", "rundll32.exe", "regsvr32.exe"))
)
| extend RiskIndicator = case(
ActionType == "FileCreated" and FileName matches regex @"\.(aspx|asp|php|jsp)$", "WebShellDrop",
ActionType == "ProcessCreated" and InitiatingProcessName =~ "SmarterMail.exe", "SuspiciousChildProcess",
"UnknownUpload"
)
| project TimeGenerated, DeviceName, ActionType, FileName, FolderPath, InitiatingProcessName, InitiatingProcessCommandLine, RiskIndicator, AccountNameDetects suspicious file creation with dangerous extensions under SmarterMail directories, or suspicious child processes spawned by the SmarterMail process, indicating potential web shell upload or post-exploitation activity via CVE-2025-52691.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate administrative scripts deployed by IT staff to the SmarterMail directory
- Antivirus or backup software creating temporary files with unusual extensions in mail directories
- SmarterMail update processes creating new executables or DLLs during patching
Other platforms for CVE-2025-52691
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 Web Shell Upload to SmarterMail Directory
Expected signal: Sysmon Event ID 11 (FileCreate) with TargetFilename containing 'SmarterMail' and ending in '.aspx'; DeviceFileEvents in Defender with ActionType=FileCreated
- Test 2Simulate SmarterMail Spawning Suspicious Child Process
Expected signal: Sysmon Event ID 1 (ProcessCreate) showing cmd.exe with parent process context; DeviceProcessEvents showing cmd.exe creation with CommandLine containing 'whoami'
- Test 3Upload Executable File to Simulated Mail Server Web Directory
Expected signal: Sysmon Event ID 11 (FileCreate) with TargetFilename matching 'C:\Temp\mailroot\webmail\update.exe'; file hash telemetry for the copied executable
- Test 4Simulate PowerShell Execution via Web Shell Context
Expected signal: Sysmon Event ID 1 (ProcessCreate) for powershell.exe with CommandLine containing reconnaissance commands; PowerShell Script Block Logging (Event ID 4104) if enabled
Unlock Pro Content
Get the full detection package for CVE-2025-52691 including response playbook, investigation guide, and atomic red team tests.