Okta Suspicious Use Of A Session Cookie

Severity: medium
Type: Alert
Time window: 1h
Match by: dtHash, userid
Author: Google Cloud Security
Source: github.com/chronicle/detection-rules

Detects when an adversary attempts to reuse a stolen web session cookie in a different device that has a different OS, IP, Browser or User Agent.

MITRE ATT&CK coverage

Tactic	Techniques
Credential Access	`T1539` Steal Web Session Cookie

References

https://sec.okta.com/sessioncookietheft

Telemetry coverage

Platform	Record / event type
Okta	System Log event type `policy.evaluate_sign_on`: Sign-on policy evaluated

Rules detecting the same action

These rules filter on the same operation.

High-Risk Admin Activity (Kusto)
Okta AiTM Session Cookie Replay (Elastic)
Okta Multiple Failed Requests To Access Applications (YARA-L)
Okta Multiple Failed Requests to Access Applications (Splunk)
Okta New Admin Console Behaviours (Sigma)
Okta New Behaviors Acessing Admin Console (Panther)
Okta Suspicious Use of a Session Cookie (Splunk)

Rule body

// Copyright 2023 Google LLC. Licensed under Apache-2.0.

rule okta_suspicious_use_of_a_session_cookie {

  meta:
    author = "Google Cloud Security"
    description = "Detects when an adversary attempts to reuse a stolen web session cookie in a different device that has a different OS, IP, Browser or User Agent."
    rule_id = "mr_913cbc7a-86c9-46a4-b822-023b4aa17106"
    rule_name = "Okta Suspicious Use Of A Session Cookie"
    reference = "https://sec.okta.com/sessioncookietheft"
    mitre_attack_tactic = "Credential Access"
    mitre_attack_technique = "Steal Web Session Cookie"
    mitre_attack_url = "https://attack.mitre.org/techniques/T1539/"
    mitre_attack_version = "v13.1"
    type = "Alert"
    data_source = "Okta"
    severity = "Medium"
    priority = "Medium"

  events:
    $login.metadata.product_name = "Okta"
    $login.metadata.vendor_name = "Okta"
    $login.metadata.event_type = "USER_UNCATEGORIZED"
    $login.metadata.product_event_type = "policy.evaluate_sign_on"
    (
        $login.security_result.action = "ALLOW" or
        $login.security_result.action = "ALLOW_WITH_MODIFICATION" or
        $login.security_result.action = "CHALLENGE"
    )
    $login.principal.user.userid = $userid
    $login.security_result.detection_fields["dtHash"] = $dtHash

  match:
    $userid, $dtHash over 1h

  outcome:
    $risk_score = max(35)
    $mitre_attack_tactic = "Credential Access"
    $mitre_attack_technique = "Steal Web Session Cookie"
    $target_os = array_distinct($login.network.http.parsed_user_agent.os)
    $dc_target_os = count_distinct($login.network.http.parsed_user_agent.os)
    $target_browser = array_distinct($login.network.http.parsed_user_agent.browser)
    $dc_target_browser = count_distinct($login.network.http.parsed_user_agent.browser)
    $target_user_agent = array_distinct($login.network.http.user_agent)
    $principal_ip = array_distinct($login.principal.ip)
    $dc_principal_ip = count_distinct($login.principal.ip)
    $principal_ip_country = array_distinct($login.principal.ip_geo_artifact.location.country_or_region)
    $principal_ip_state = array_distinct($login.principal.ip_geo_artifact.location.state)
    $principal_ip_city = array_distinct($login.principal.location.city)
    $dc_principal_ip_city = count_distinct($login.principal.location.city)
    $security_result_summary = array_distinct($login.security_result.summary)
    $principal_user_managers_email_addresses = array_distinct($login.principal.user.managers.email_addresses)
    $principal_user_userid = array_distinct($login.principal.user.userid)

  condition:
    $login and $dc_principal_ip > 1 and ($dc_target_browser > 1 or $dc_target_os > 1)
}

YARA-L rule structure

Condition

Fires when at least one $login event in the 1h window and $dc_principal_ip > 1 and $dc_target_browser > 1 or $dc_target_os > 1.

Events

`$login` `USER_UNCATEGORIZED`

metadata.product_event_type = "policy.evaluate_sign_on"
security_result.action is one of:
- ALLOW
- ALLOW_WITH_MODIFICATION
- CHALLENGE

Match and correlation

Match key: $dtHash (security_result.detection_fields["dtHash"]), $userid (principal.user.userid)
Within: 1h

Outcome

Outcome variables add context to a detection. When the rule generates an alert, $risk_score is displayed with it.

Field	Expression
`risk_score`	`max(35)`
`target_os`	`array_distinct($login.network.http.parsed_user_agent.os)`
`dc_target_os`	`count_distinct($login.network.http.parsed_user_agent.os)`
`target_browser`	`array_distinct($login.network.http.parsed_user_agent.browser)`
`dc_target_browser`	`count_distinct($login.network.http.parsed_user_agent.browser)`
`target_user_agent`	`array_distinct($login.network.http.user_agent)`
`principal_ip`	`array_distinct($login.principal.ip)`
`dc_principal_ip`	`count_distinct($login.principal.ip)`
`principal_ip_country`	`array_distinct($login.principal.ip_geo_artifact.location.country_or_region)`
`principal_ip_state`	`array_distinct($login.principal.ip_geo_artifact.location.state)`
`principal_ip_city`	`array_distinct($login.principal.location.city)`
`dc_principal_ip_city`	`count_distinct($login.principal.location.city)`
`security_result_summary`	`array_distinct($login.security_result.summary)`
`principal_user_managers_email_addresses`	`array_distinct($login.principal.user.managers.email_addresses)`
`principal_user_userid`	`array_distinct($login.principal.user.userid)`