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Detection rules › Sigma

PetitPotam Suspicious Kerberos TGT Request

Status
test
Severity
high
Log source
product windows, service security
Author
Mauricio Velazco, Michael Haag
Source
github.com/SigmaHQ/sigma

Detect suspicious Kerberos TGT requests. Once an attacer obtains a computer certificate by abusing Active Directory Certificate Services in combination with PetitPotam, the next step would be to leverage the certificate for malicious purposes. One way of doing this is to request a Kerberos Ticket Granting Ticket using a tool like Rubeus. This request will generate a 4768 event with some unusual fields depending on the environment. This analytic will require tuning, we recommend filtering Account_Name to the Domain Controller computer accounts.

MITRE ATT&CK coverage

TacticTechniques
Credential AccessT1187 Forced Authentication

Event coverage

ProviderEventTitle
Security-AuditingEvent ID 4768A Kerberos authentication ticket (TGT) was requested.

Rule body yaml

title: PetitPotam Suspicious Kerberos TGT Request
id: 6a53d871-682d-40b6-83e0-b7c1a6c4e3a5
status: test
description: |
    Detect suspicious Kerberos TGT requests.
    Once an attacer obtains a computer certificate by abusing Active Directory Certificate Services in combination with PetitPotam, the next step would be to leverage the certificate for malicious purposes.
    One way of doing this is to request a Kerberos Ticket Granting Ticket using a tool like Rubeus.
    This request will generate a 4768 event with some unusual fields depending on the environment.
    This analytic will require tuning, we recommend filtering Account_Name to the Domain Controller computer accounts.
references:
    - https://github.com/topotam/PetitPotam
    - https://isc.sans.edu/forums/diary/Active+Directory+Certificate+Services+ADCS+PKI+domain+admin+vulnerability/27668/
    - https://github.com/splunk/security_content/blob/88d689fe8a055d8284337b9fad5d9152b42043db/detections/endpoint/petitpotam_suspicious_kerberos_tgt_request.yml
author: Mauricio Velazco, Michael Haag
date: 2021-09-02
modified: 2022-10-05
tags:
    - attack.credential-access
    - attack.t1187
logsource:
    product: windows
    service: security
    definition: 'The advanced audit policy setting "Account Logon > Kerberos Authentication Service" must be configured for Success/Failure'
detection:
    selection:
        EventID: 4768
        TargetUserName|endswith: '$'
        CertThumbprint|contains: '*'
    filter_local:
        IpAddress: '::1'
    filter_thumbprint:
        CertThumbprint: ''
    condition: selection and not 1 of filter_*
falsepositives:
    - False positives are possible if the environment is using certificates for authentication. We recommend filtering Account_Name to the Domain Controller computer accounts.
level: high

Stages and Predicates

Stage 0: condition

selection and not 1 of filter_*

Stage 1: selection

selection:
    EventID: 4768
    TargetUserName|endswith: '$'
    CertThumbprint|contains: '*'

Stage 2: not filter_*

filter_local:
    IpAddress: '::1'
filter_thumbprint:
    CertThumbprint: ''

Exclusions

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

FieldKindExcluded values
IpAddresseq::1

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
CertThumbprintmatch
  • *
TargetUserNameends_with
  • $ corpus 7 (sigma 5, kusto 2)