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Windows SIP WinVerifyTrust Failed Trust Validation

Status
production
Severity
low
Group by
UserData_Xml, computer_name
Author
Michael Haag, Splunk
Source
github.com/splunk/security_content

The following analytic detects failed trust validation attempts using Windows Event Log - CAPI2 (CryptoAPI 2). It specifically triggers on EventID 81, which indicates that "The digital signature of the object did not verify." This detection leverages the CAPI2 Operational log to identify instances where digital signatures fail to validate. Monitoring this activity is crucial as it can indicate attempts to execute untrusted or potentially malicious binaries. If confirmed malicious, this activity could allow attackers to bypass security controls and execute unauthorized code, leading to potential system compromise.

MITRE ATT&CK coverage

TacticTechniques
Defense ImpairmentT1553.003 Subvert Trust Controls: SIP and Trust Provider Hijacking

Event coverage

ProviderEventTitle
CAPI2Event ID 81For more details for this event, please refer to the "Details" section

Rule body splunk

name: Windows SIP WinVerifyTrust Failed Trust Validation
id: 6ffc7f88-415b-4278-a80d-b957d6539e1a
version: 9
creation_date: '2023-10-10'
modification_date: '2026-05-13'
author: Michael Haag, Splunk
status: production
type: Anomaly
description: The following analytic detects failed trust validation attempts using Windows Event Log - CAPI2 (CryptoAPI 2). It specifically triggers on EventID 81, which indicates that "The digital signature of the object did not verify." This detection leverages the CAPI2 Operational log to identify instances where digital signatures fail to validate. Monitoring this activity is crucial as it can indicate attempts to execute untrusted or potentially malicious binaries. If confirmed malicious, this activity could allow attackers to bypass security controls and execute unauthorized code, leading to potential system compromise.
data_source:
    - Windows Event Log CAPI2 81
search: |-
    `capi2_operational` EventID=81 "The digital signature of the object did not verify."
      | xmlkv UserData_Xml
      | stats count min(_time) as firstTime max(_time) as lastTime
        BY Computer, UserData_Xml
      | rename Computer as dest
      | `windows_sip_winverifytrust_failed_trust_validation_filter`
how_to_implement: To implement this analytic, one will need to enable the Microsoft-Windows-CAPI2/Operational log within the Windows Event Log. Note this is a debug log for many purposes, and the analytic only focuses in on EventID 81. Review the following gist for additional enabling information.
known_false_positives: False positives may be present in some instances of legitimate binaries with invalid signatures. Filter as needed.
references:
    - https://attack.mitre.org/techniques/T1553/003/
    - https://specterops.io/wp-content/uploads/sites/3/2022/06/SpecterOps_Subverting_Trust_in_Windows.pdf
    - https://github.com/gtworek/PSBits/tree/master/SIP
    - https://github.com/mattifestation/PoCSubjectInterfacePackage
    - https://pentestlab.blog/2017/11/06/hijacking-digital-signatures/
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search  dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: Failed trust validation via the CryptoAPI 2 on $dest$ for a binary.
analytic_story:
    - Subvert Trust Controls SIP and Trust Provider Hijacking
asset_type: Endpoint
mitre_attack_id:
    - T1553.003
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1553.003/sip/capi2-operational.log
          source: XmlWinEventLog:Microsoft-Windows-CAPI2/Operational
          sourcetype: XmlWinEventLog
      test_type: unit

Stages and Predicates

Stage 1: search

`capi2_operational` EventID=81 "The digital signature of the object did not verify."

Stage 2: xmlkv

| xmlkv UserData_Xml

Stage 3: stats

| stats count min(_time) as firstTime max(_time) as lastTime
    BY Computer, UserData_Xml

Stage 4: rename

| rename Computer as dest

Stage 5: search

| `windows_sip_winverifytrust_failed_trust_validation_filter`

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
EventIDeq
  • 81

Search terms

Bare-string tokens in the SPL search body. Splunk matches each token against _raw (the untyped raw event text) anywhere it appears, not against a specific field. These don't surface in the Indicators table because they aren't predicates on a known field.

StageTerm
1"The digital signature of the object did not verify."