Potential password in username

name: Potential password in username
id: 5ced34b4-ab32-4bb0-8f22-3b8f186f0a38
version: 7
date: '2026-02-25'
author: Mikael Bjerkeland, Splunk
status: production
type: Hunting
description: The following analytic identifies instances where users may have mistakenly entered their passwords in the username field during authentication attempts. It detects this by analyzing failed authentication events with usernames longer than 7 characters and high Shannon entropy, followed by a successful authentication from the same source to the same destination. This activity is significant as it can indicate potential security risks, such as password exposure. If confirmed malicious, attackers could exploit this to gain unauthorized access, leading to potential data breaches or further compromise of the system.
data_source:
    - Linux Secure
search: |-
    | tstats `security_content_summariesonly` earliest(_time) AS starttime latest(_time) AS endtime latest(sourcetype) AS sourcetype values(Authentication.src) AS src values(Authentication.dest) AS dest count FROM datamodel=Authentication
      WHERE nodename=Authentication.Failed_Authentication
      BY "Authentication.user"
    | `drop_dm_object_name(Authentication)`
    | lookup ut_shannon_lookup word AS user
    | where ut_shannon>3 AND len(user)>=8 AND mvcount(src) == 1
    | sort count, - ut_shannon
    | eval incorrect_cred=user
    | eval endtime=endtime+1000
    | map maxsearches=70 search="
    | tstats `security_content_summariesonly` earliest(_time) AS starttime latest(_time) AS endtime latest(sourcetype) AS sourcetype values(Authentication.src) AS src values(Authentication.dest) AS dest count FROM datamodel=Authentication
      WHERE nodename=Authentication.Successful_Authentication Authentication.src=\"$src$\" Authentication.dest=\"$dest$\" sourcetype IN (\"$sourcetype$\") earliest=\"$starttime$\" latest=\"$endtime$\" BY \"Authentication.user\"
    | `drop_dm_object_name(\"Authentication\")`
    | `potential_password_in_username_false_positive_reduction`
    | eval incorrect_cred=\"$incorrect_cred$\"
    | eval ut_shannon=\"$ut_shannon$\"
    | sort count"
    | where user!=incorrect_cred
    | outlier action=RM count
    | `potential_password_in_username_filter`
how_to_implement: To successfully implement this search, you need to have relevant authentication logs mapped to the Authentication data model. You also need to have the Splunk TA URL Toolbox (https://splunkbase.splunk.com/app/2734/) installed. The detection must run with a time interval shorter than endtime+1000.
known_false_positives: Valid usernames with high entropy or source/destination system pairs with multiple authenticating users will make it difficult to identify the real user authenticating.
references:
    - https://medium.com/@markmotig/search-for-passwords-accidentally-typed-into-the-username-field-975f1a389928
tags:
    analytic_story:
        - Credential Dumping
        - Insider Threat
    asset_type: Endpoint
    mitre_attack_id:
        - T1078.003
        - T1552.001
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: access
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1552.001/password_in_username/linux_secure.log
          source: /var/log/secure
          sourcetype: linux_secure