Detection rules › Splunk
Cisco Duo Policy Deny Access
The following analytic identifies instances where a Duo administrator creates or updates a policy to explicitly deny user access within the Duo environment. It detects this behavior by searching Duo administrator activity logs for policy creation or update actions where the authentication status is set to "Deny access." By correlating these events with user and admin details, the analytic highlights potential misuse or malicious changes to access policies. This behavior is critical for a SOC to monitor, as unauthorized or suspicious denial of access policies can indicate insider threats, account compromise, or attempts to disrupt legitimate user access. The impact of such an attack may include denial of service to critical accounts, disruption of business operations, or the masking of further malicious activity by preventing targeted users from accessing resources. Early detection enables rapid investigation and remediation to maintain organizational security and availability.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Persistence | T1556 Modify Authentication Process |
| Defense Impairment | T1556 Modify Authentication Process |
| Credential Access | T1556 Modify Authentication Process |
Rule body splunk
name: Cisco Duo Policy Deny Access
id: abf39464-ed43-4d69-a56c-02750032a3fb
version: 6
creation_date: '2025-07-10'
modification_date: '2026-05-13'
author: Patrick Bareiss, Splunk
status: production
type: TTP
description: The following analytic identifies instances where a Duo administrator creates or updates a policy to explicitly deny user access within the Duo environment. It detects this behavior by searching Duo administrator activity logs for policy creation or update actions where the authentication status is set to "Deny access." By correlating these events with user and admin details, the analytic highlights potential misuse or malicious changes to access policies. This behavior is critical for a SOC to monitor, as unauthorized or suspicious denial of access policies can indicate insider threats, account compromise, or attempts to disrupt legitimate user access. The impact of such an attack may include denial of service to critical accounts, disruption of business operations, or the masking of further malicious activity by preventing targeted users from accessing resources. Early detection enables rapid investigation and remediation to maintain organizational security and availability.
data_source:
- Cisco Duo Administrator
search: |-
`cisco_duo_administrator` action=policy_update OR action=policy_create
| spath input=description
| search auth_status="Deny access"
| rename object as user
| stats count min(_time) as firstTime max(_time) as lastTime
BY action actionlabel description
user admin_email
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
| `cisco_duo_policy_deny_access_filter`
how_to_implement: The analytic leverages Duo activity logs to be ingested using the Cisco Security Cloud App (https://splunkbase.splunk.com/app/7404).
known_false_positives: No false positives have been identified at this time.
references:
- https://splunkbase.splunk.com/app/7404
drilldown_searches:
- name: View the detection results for - "$user$"
search: '%original_detection_search% | search user = "$user$"'
earliest_offset: $info_min_time$
latest_offset: $info_max_time$
- name: View risk events for the last 7 days for - "$user$"
search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$") | 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"
finding:
title: A policy has been created or updated to deny access by user $user$ with email $admin_email$
entity:
field: user
type: user
score: 50
analytic_story:
- Cisco Duo Suspicious Activity
asset_type: Identity
mitre_attack_id:
- T1556
product:
- Splunk Enterprise
- Splunk Enterprise Security
- Splunk Cloud
category: application
security_domain: identity
tests:
- name: True Positive Test
attack_data:
- data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1556/cisco_duo_policy_deny_access/cisco_duo_administrator.json
source: duo
sourcetype: cisco:duo:administrator
test_type: unit
Stages and Predicates
Stage 1: search
`cisco_duo_administrator` action=policy_update OR action=policy_create
Stage 2: spath
| spath input=description
Stage 3: search
| search auth_status="Deny access"
Stage 4: rename
| rename object as user
Stage 5: stats
| stats count min(_time) as firstTime max(_time) as lastTime
BY action actionlabel description
user admin_email
Stage 6: search
| `security_content_ctime(firstTime)`
Stage 7: search
| `security_content_ctime(lastTime)`
Stage 8: search
| `cisco_duo_policy_deny_access_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.
| Field | Kind | Values |
|---|---|---|
action | eq |
|
auth_status | eq |
|
sourcetype | eq |
|