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.

Known false positives

False positives may be present in some instances of legitimate binaries with invalid signatures. Filter as needed.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Impairment	`T1553.003` Subvert Trust Controls: SIP and Trust Provider Hijacking

Telemetry coverage

Provider	Record / event type
CAPI2	Event ID 81: For more details for this event, please refer to the "Details" section

Rule body

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/
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

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

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`EventID`	eq	`81`	`field:"EventID" kind:eq value:"81"`

Search terms

These SPL tokens match against raw event text.

Stage	Term
1	`"The digital signature of the object did not verify."`