GCP Multiple Failed MFA Requests For User

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

The following analytic detects multiple failed multi-factor authentication (MFA) requests for a single user within a Google Cloud Platform (GCP) tenant. It triggers when 10 or more MFA prompts fail within a 5-minute window, using Google Workspace login failure events. This behavior is significant as it may indicate an adversary attempting to bypass MFA by bombarding the user with repeated authentication requests. If confirmed malicious, this activity could lead to unauthorized access, allowing attackers to compromise accounts and potentially escalate privileges within the GCP environment.

Known false positives

Multiple Failed MFA requests may also be a sign of authentication or application issues. Filter as needed.

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 Authentication Failed During MFA Challenge (Splunk)
GCP Multiple Users Failing To Authenticate From Ip (Splunk)
GCP Unusual Number of Failed Authentications From Ip (Splunk)

Rule body

name: GCP Multiple Failed MFA Requests For User
id: cbb3cb84-c06f-4393-adcc-5cb6195621f1
version: 12
creation_date: '2022-08-25'
modification_date: '2026-05-13'
author: Mauricio Velazco, Splunk
status: production
type: TTP
description: The following analytic detects multiple failed multi-factor authentication (MFA) requests for a single user within a Google Cloud Platform (GCP) tenant. It triggers when 10 or more MFA prompts fail within a 5-minute window, using Google Workspace login failure events. This behavior is significant as it may indicate an adversary attempting to bypass MFA by bombarding the user with repeated authentication requests. If confirmed malicious, this activity could lead to unauthorized access, allowing attackers to compromise accounts and potentially escalate privileges within the GCP environment.
data_source:
    - Google Workspace
search: |-
    `gws_reports_login` event.name=login_failure `gws_login_mfa_methods`
      | bucket span=5m _time
      | stats dc(_raw) AS mfa_prompts values(user) AS user
        BY src_ip, login_challenge_method, _time
      | where mfa_prompts >= 10
      | `gcp_multiple_failed_mfa_requests_for_user_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. We would also recommend tuning the detection by adjusting the window `span` and `mfa_prompts` threshold values according to your environment. Specifically, this analytic leverages the User log events.
known_false_positives: Multiple Failed MFA requests may also be a sign of authentication or application issues. Filter as needed.
references:
    - https://www.mandiant.com/resources/blog/russian-targeting-gov-business
    - https://arstechnica.com/information-technology/2022/03/lapsus-and-solar-winds-hackers-both-use-the-same-old-trick-to-bypass-mfa/
    - https://therecord.media/russian-hackers-bypass-2fa-by-annoying-victims-with-repeated-push-notifications/
    - https://attack.mitre.org/techniques/T1621/
    - https://attack.mitre.org/techniques/T1078/004/
finding:
    title: Multiple Failed MFA requests for user $user$
    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: `bucket`

| bucket span=5m _time

Stage 3: `stats`

| stats dc(_raw) AS mfa_prompts values(user) AS user
    BY src_ip, login_challenge_method, _time

Stage 4: `where`

| where mfa_prompts >= 10

Stage 5: `search`

| `gcp_multiple_failed_mfa_requests_for_user_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`
`mfa_prompts`	ge	`10`	`field:"mfa_prompts" kind:ge value:"10"`
`sourcetype`	eq	`gws:reports:login`	`field:"sourcetype" kind:eq value:"gws:reports:login"`