GCP Authentication Failed During MFA Challenge

Status: production
Severity: medium
Group by: login_challenge_method, src_ip, user
Author: Bhavin Patel, Mauricio Velazco, Splunk
Source: github.com/splunk/security_content

The following analytic detects failed authentication attempts during the Multi-Factor Authentication (MFA) challenge on a Google Cloud Platform (GCP) tenant. It uses Google Workspace login failure events to identify instances where MFA methods were challenged but not successfully completed. This activity is significant as it may indicate an adversary attempting to access an account with compromised credentials despite MFA protection. If confirmed malicious, this could lead to unauthorized access attempts, potentially compromising sensitive data and resources within the GCP environment.

Known false positives

Legitimate users may miss to reply the MFA challenge within the time window or deny it by mistake.

MITRE ATT&CK coverage

Tactic	Techniques
Resource Development	`T1586.003` Compromise Accounts: Cloud Accounts
Initial Access	`T1078.004` Valid Accounts: Cloud Accounts
Persistence	`T1078.004` Valid Accounts: Cloud Accounts
Privilege Escalation	`T1078.004` Valid Accounts: Cloud Accounts
Stealth	`T1078.004` Valid Accounts: Cloud Accounts
Credential Access	`T1621` Multi-Factor Authentication Request Generation

Telemetry coverage

Platform	Record / event type
Google Workspace	login_failure: Login Failure

Rules detecting the same action

These rules filter on the same operation.

GCP Multiple Failed MFA Requests For User (Splunk)
GCP Multiple Users Failing To Authenticate From Ip (Splunk)
GCP Unusual Number of Failed Authentications From Ip (Splunk)

Rule body

name: GCP Authentication Failed During MFA Challenge
id: 345f7e1d-a3fe-4158-abd8-e630f9878323
version: 13
creation_date: '2022-10-14'
modification_date: '2026-05-13'
author: Bhavin Patel, Mauricio Velazco, Splunk
status: production
type: TTP
description: The following analytic detects failed authentication attempts during the Multi-Factor Authentication (MFA) challenge on a Google Cloud Platform (GCP) tenant. It uses Google Workspace login failure events to identify instances where MFA methods were challenged but not successfully completed. This activity is significant as it may indicate an adversary attempting to access an account with compromised credentials despite MFA protection. If confirmed malicious, this could lead to unauthorized access attempts, potentially compromising sensitive data and resources within the GCP environment.
data_source:
    - Google Workspace login_failure
search: |-
    `gws_reports_login` event.name=login_failure `gws_login_mfa_methods`
      | stats count min(_time) as firstTime max(_time) as lastTime
        BY user, src_ip, login_challenge_method
      | `gcp_authentication_failed_during_mfa_challenge_filter`
how_to_implement: You must install the latest version of Splunk Add-on for Google Workspace from Splunkbase (https://splunkbase.splunk.com/app/5556) which allows Splunk administrators to collect Google Workspace event data in Splunk using Google Workspace APIs. Specifically, this analytic leverages the User log events.
known_false_positives: Legitimate users may miss to reply the MFA challenge within the time window or deny it by mistake.
references:
    - https://attack.mitre.org/techniques/T1621/
    - https://attack.mitre.org/techniques/T1078/004/
finding:
    title: User $user$ failed to pass MFA challenge
    entity:
        field: user
        type: user
        score: 50
threat_objects:
    - field: src_ip
      type: ip_address
analytic_story:
    - GCP Account Takeover
    - Scattered Lapsus$ Hunters
asset_type: Google Cloud Platform tenant
mitre_attack_id:
    - T1078.004
    - T1586.003
    - T1621
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: cloud
security_domain: identity

Stages and Predicates

Stage 1: `search`

`gws_reports_login` event.name=login_failure `gws_login_mfa_methods`

Stage 2: `stats`

| stats count min(_time) as firstTime max(_time) as lastTime
    BY user, src_ip, login_challenge_method

Stage 3: `search`

| `gcp_authentication_failed_during_mfa_challenge_filter`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`event.name`	eq	`login_failure`	`field:"event.name" kind:eq value:"login_failure"`
`event.parameters{}.multiValue{}`	in	`"backup_code"` `"google_authenticator"` `"google_prompt"` `"idv_any_phone"` `"idv_preregistered_phone"` `"internal_two_factor"` `"knowledge_employee_id"` `"knowledge_preregistered_email"` `"knowledge_preregistered_phone"` `"login_location"` `"offline_otp"` `"security_key"` `"security_key_otp"`	`field:"event.parameters{}.multiValue{}" kind:in`
`sourcetype`	eq	`gws:reports:login`	`field:"sourcetype" kind:eq value:"gws:reports:login"`