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Mailsniper Invoke functions

Author
Teoderick Contreras, Splunk
Source
upstream

The following analytic detects the execution of known MailSniper PowerShell functions on a machine. It leverages PowerShell logs (EventCode 4104) to identify specific script block text associated with MailSniper activities. This behavior is significant as MailSniper is often used by attackers to harvest sensitive emails from compromised Exchange servers. If confirmed malicious, this activity could lead to unauthorized access to sensitive email data, credential theft, and further compromise of the email infrastructure.

MITRE ATT&CK coverage

TacticTechniques
CollectionT1114.001 Email Collection: Local Email Collection

Event coverage

ProviderEvent IDTitle
PowerShell4104Creating Scriptblock text (MessageNumber of MessageTotal).

Stages and Predicates

Stage 1: search

search EventCode=4104 ScriptBlockText IN ("*Invoke-AddGmailRule*", "*Invoke-DomainHarvestOWA*", "*Invoke-GlobalMailSearch*", "*Invoke-GlobalO365MailSearch*", "*Invoke-InjectGEvent*", "*Invoke-InjectGEventAPI*", "*Invoke-MonitorCredSniper*", "*Invoke-OpenInboxFinder*", "*Invoke-PasswordSprayEAS*", "*Invoke-PasswordSprayEWS*", "*Invoke-PasswordSprayOWA*", "*Invoke-SearchGmail*", "*Invoke-SelfSearch*", "*Invoke-UsernameHarvestEAS*", "*Invoke-UsernameHarvestOWA*")

Stage 2: fillnull

fillnull

Stage 3: stats

stats BY dest, signature, signature_id, user_id, vendor_product, EventID, Guid, Opcode, Name, Path, ProcessID, ScriptBlockId, ScriptBlockText

Stage 4: search

search

Stage 5: search

search

Stage 6: search

search `macro`

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
EventCodeeq
  • 4104 corpus 108 (splunk 108)
ScriptBlockTextin
  • "*Invoke-AddGmailRule*"
  • "*Invoke-DomainHarvestOWA*"
  • "*Invoke-GlobalMailSearch*"
  • "*Invoke-GlobalO365MailSearch*"
  • "*Invoke-InjectGEvent*"
  • "*Invoke-InjectGEventAPI*"
  • "*Invoke-MonitorCredSniper*"
  • "*Invoke-OpenInboxFinder*"
  • "*Invoke-PasswordSprayEAS*"
  • "*Invoke-PasswordSprayEWS*"
  • "*Invoke-PasswordSprayOWA*"
  • "*Invoke-SearchGmail*"
  • "*Invoke-SelfSearch*"
  • "*Invoke-UsernameHarvestEAS*"
  • "*Invoke-UsernameHarvestOWA*"

Neighbors

Broader alternatives (more inclusive than this rule)

These rules match a superset of what this rule catches. They cover the same events plus more. Use them if you want wider coverage and can absorb more false positives.