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Detection rules › Splunk

Wbemprox COM Object Execution

Author
Teoderick Contreras, Splunk
Source
upstream

The following analytic detects a suspicious process loading a COM object from wbemprox.dll, fastprox.dll, or wbemcomn.dll. It leverages Sysmon EventCode 7 to identify instances where these DLLs are loaded by processes not typically associated with them, excluding known legitimate processes and directories. This activity is significant as it may indicate an attempt by threat actors to abuse COM objects for privilege escalation or evasion of detection mechanisms. If confirmed malicious, this could allow attackers to gain elevated privileges or maintain persistence within the environment, posing a significant security risk.

MITRE ATT&CK coverage

TacticTechniques
Defense EvasionT1218.003 System Binary Proxy Execution: CMSTP

Event coverage

ProviderEvent IDTitle
Sysmon7Image loaded

Stages and Predicates

Stage 1: search

search NOT (NOT Image IN ("*\\program files*", "*\\wbem\\*", "*\\windows\\*") process_name IN ("WmiApSrv.exe", "unsecapp.exe", "wmiprvse.exe")) EventCode=7 ImageLoaded IN ("*\\fastprox.dll", "*\\wbemcomn.dll", "*\\wbemprox.dll")

Stage 2: fillnull

fillnull

Stage 3: stats

stats BY Image, ImageLoaded, dest, loaded_file, loaded_file_path, original_file_name, process_exec, process_guid, process_hash, process_id, process_name, process_path, service_dll_signature_exists, service_dll_signature_verified, signature, signature_id, user_id, vendor_product

Stage 4: search

search

Stage 5: search

search

Stage 6: search

search `macro`

Exclusions

Top-level NOT(...) conjuncts — predicates this rule actively suppresses.

StageFieldKindExcluded values
1Imagein"*\\program files*", "*\\wbem\\*", "*\\windows\\*"
2process_namein"WmiApSrv.exe", "unsecapp.exe", "wmiprvse.exe"

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
  • 7 corpus 35 (splunk 35)
Imagein
  • "*\\program files*" corpus 2 (splunk 2)
  • "*\\wbem\\*"
  • "*\\windows\\*" corpus 2 (splunk 2)
ImageLoadedin
  • "*\\fastprox.dll" corpus 2 (splunk 2)
  • "*\\wbemcomn.dll" corpus 2 (splunk 2)
  • "*\\wbemprox.dll" corpus 2 (splunk 2)

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.