Detect SmarterMail Unrestricted File Upload Exploitation (CVE-2025-52691) in Google Chronicle
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
YARA-L Detection Query
rule cve_2025_52691_smartermail_file_upload {
meta:
author = "df00tech Detection Engineering"
description = "Detects unrestricted file upload exploitation in SmarterMail (CVE-2025-52691)"
severity = "CRITICAL"
priority = "HIGH"
reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-52691"
events:
(
$e.metadata.event_type = "FILE_CREATION"
and re.regex($e.target.file.full_path, `(?i)(smartermail|mailroot|webmail)`)
and re.regex($e.target.file.full_path, `(?i)\.(aspx|asp|php|jsp|cfm|cgi|pl|exe|dll|bat|cmd|ps1|vbs|hta)$`)
)
or
(
$e.metadata.event_type = "PROCESS_LAUNCH"
and re.regex($e.principal.process.file.full_path, `(?i)smartermail\.exe`)
and re.regex($e.target.process.file.full_path, `(?i)(cmd|powershell|wscript|cscript|mshta|certutil)\.exe`)
)
condition:
$e
}Chronicle YARA-L rule detecting file creation events with dangerous extensions in SmarterMail paths and suspicious child processes launched by SmarterMail, covering key indicators of CVE-2025-52691 exploitation.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate SmarterMail administrative operations creating ASPX or executable files during updates
- Security tooling spawned from service accounts associated with SmarterMail
- Developer environments where test scripts are uploaded to mail server directories for integration testing
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.