Detect Web Portal Capture in Splunk
Adversaries may install code on externally facing portals, such as a VPN login page, to capture and transmit credentials of users who attempt to log into the service. A compromised login page may log provided user credentials before logging the user in to the service. This variation on input capture may be conducted post-compromise using legitimate administrative access as a backup measure to maintain network access through External Remote Services and Valid Accounts, or as part of the initial compromise by exploitation of the externally facing web service. Notable examples include IceApple's OWA credential logger, WARPWIRE targeting Ivanti VPN portals, and Winter Vivern mimicking government email logon sites.
MITRE ATT&CK
- Tactic
- Collection Credential Access
- Technique
- T1056 Input Capture
- Sub-technique
- T1056.003 Web Portal Capture
- Canonical reference
- https://attack.mitre.org/techniques/T1056/003/
SPL Detection Query
index=wineventlog (sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" OR sourcetype="WinEventLog:Security")
(
(EventCode=11 (TargetFilename="*\\inetpub\\*" OR TargetFilename="*\\wwwroot\\*" OR TargetFilename="*\\owa\\*" OR TargetFilename="*\\ecp\\*" OR TargetFilename="*\\vpn\\*" OR TargetFilename="*\\sslvpn\\*")
(TargetFilename="*.aspx" OR TargetFilename="*.asp" OR TargetFilename="*.php" OR TargetFilename="*.js" OR TargetFilename="*.config" OR TargetFilename="*.jsp")
(Image="*\\w3wp.exe" OR Image="*\\iisexpress.exe" OR Image="*\\httpd.exe" OR Image="*\\nginx.exe"))
OR
(EventCode=1 (ParentImage="*\\w3wp.exe" OR ParentImage="*\\iisexpress.exe" OR ParentImage="*\\httpd.exe")
(Image="*\\cmd.exe" OR Image="*\\powershell.exe" OR Image="*\\sh.exe" OR Image="*\\bash.exe" OR Image="*\\net.exe" OR Image="*\\whoami.exe"))
OR
(EventCode=1 (Image="*\\w3wp.exe" OR Image="*\\iisexpress.exe")
(CommandLine="*password*" OR CommandLine="*credential*" OR CommandLine="*username*" OR CommandLine="*passwd*"))
)
| eval EventType=case(
EventCode=11, "WebFileCreation",
EventCode=1 AND match(ParentImage, "(w3wp|iisexpress|httpd|nginx)"), "WebShellSpawn",
EventCode=1 AND match(Image, "(w3wp|iisexpress)"), "WebProcessExec",
true(), "Unknown")
| eval WebPortalIndicator=if(match(TargetFilename, "(inetpub|wwwroot|owa|ecp|vpn|sslvpn|exchange)"), 1, 0)
| eval CredentialKeyword=if(match(lower(CommandLine), "(password|passwd|credential|username|login|auth|token|session)"), 1, 0)
| eval SpawnedShell=if(match(Image, "(cmd\.exe|powershell\.exe|sh\.exe|bash\.exe)") AND match(ParentImage, "(w3wp|iisexpress|httpd|nginx)"), 1, 0)
| eval SuspicionScore=WebPortalIndicator + CredentialKeyword + SpawnedShell
| table _time, host, EventCode, EventType, Image, CommandLine, ParentImage, ParentCommandLine, TargetFilename, User, SuspicionScore
| sort - _timeDetects web portal credential capture using Sysmon events. Monitors for file creation events (EventCode 11) in IIS/web portal directories by web server processes, and web server processes (w3wp.exe, iisexpress.exe, httpd.exe) spawning command shells (EventCode 1). Assigns a suspicion score based on multiple indicators: web portal path presence, credential-related keywords in command lines, and shell processes spawned by web servers.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Legitimate web application deployments via deployment pipelines that use w3wp.exe to create or modify web files
- IIS application pool management scripts that legitimately spawn cmd.exe or powershell.exe for configuration
- Web application frameworks generating compiled or cached files (e.g., ASP.NET temporary files) in web directories
- Automated certificate renewal scripts modifying web.config or application configuration files
Other platforms for T1056.003
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 Credential Capture File Creation in IIS Web Root
Expected signal: Sysmon Event ID 11 (FileCreate): TargetFilename=C:\inetpub\wwwroot\login_helper.php, Image=cmd.exe. DeviceFileEvents: ActionType=FileCreated, FolderPath contains \inetpub\wwwroot\, FileName=login_helper.php. Security Event 4663 if SACL auditing is enabled on the wwwroot directory.
- Test 2Web Server Process Spawning Command Shell (WebShell Simulation)
Expected signal: Sysmon Event ID 1 (Process Create): Image=cmd.exe, ParentImage=powershell.exe, CommandLine containing 'whoami'. Sysmon Event ID 11: TargetFilename=C:\Windows\Temp\webshell_test.txt. Security Event 4688 with NewProcessName=cmd.exe if process creation auditing is enabled.
- Test 3Inject Credential Capture Code into Existing ASPX Login Page
Expected signal: Sysmon Event ID 11 (FileCreate/Modify): TargetFilename=C:\inetpub\wwwroot\testportal\login.aspx, Image=powershell.exe. DeviceFileEvents: ActionType=FileModified, FileName=login.aspx, FolderPath contains \inetpub\wwwroot\. Security Event 4663 if SACL file auditing is configured on the web root.
- Test 4Simulate Credential Exfiltration via Web Server Outbound HTTP
Expected signal: Sysmon Event ID 3 (Network Connection): Image=powershell.exe, DestinationIp=127.0.0.1, DestinationPort=9001, Protocol=tcp. DeviceNetworkEvents: InitiatingProcessFileName=powershell.exe, RemotePort=9001. PowerShell ScriptBlock Log Event ID 4104 showing the HTTP POST with credential parameters.
References (8)
- https://attack.mitre.org/techniques/T1056/003/
- https://www.volexity.com/blog/2015/10/07/virtual-private-keylogging-cisco-web-vpns-leveraged-for-access-and-persistence/
- https://www.mandiant.com/resources/blog/cutting-edge-suspected-apt-targets-ivanti-connect-secure-vpn-in-new-zero-day-exploitation
- https://www.crowdstrike.com/blog/iceapple-a-novel-internet-information-services-post-exploitation-framework/
- https://www.sentinelone.com/labs/winter-vivern-all-summer-long-unattributed-threat-actor-from-russia-or-belarus/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1056.003/T1056.003.md
- https://learn.microsoft.com/en-us/iis/manage/provisioning-and-managing-iis/configure-logging-in-iis
- https://docs.microsoft.com/en-us/windows/security/threat-protection/auditing/audit-file-system
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