AWS STS GetSessionToken by IAM User

Description

Detects an IAM user calling STS GetSessionToken to obtain temporary credentials. Attackers who have compromised long-term IAM credentials may use GetSessionToken to generate short-lived session tokens for lateral movement or to bypass IP-based policies that apply only to long-term credentials.

Query · python

from panther_aws_helpers import aws_cloudtrail_success, aws_rule_context


def rule(event):
    if not aws_cloudtrail_success(event):
        return False
    return (
        event.get("eventSource") == "sts.amazonaws.com"
        and event.get("eventName") == "GetSessionToken"
        and event.deep_get("userIdentity", "type") == "IAMUser"
    )


def title(event):
    user = event.deep_get("userIdentity", "userName", default="<unknown>")
    account = event.get("recipientAccountId", "<unknown>")
    return f"IAM user [{user}] called GetSessionToken in account [{account}]"


def alert_context(event):
    return aws_rule_context(event)

Analyst notes

  1. Query CloudTrail for all API calls by userIdentity:arn in the 6 hours before and after this alert to establish what the session token was used for
  2. Check if sourceIPAddress is associated with known corporate network ranges, VPN endpoints, or cloud provider IP ranges
  3. Find other alerts for this userIdentity:userName in the past 30 days to determine if GetSessionToken usage is part of normal workflow
Raw source AWS STS GetSessionToken by IAM User · Panther Python
Esc
Published by panther-labs/panther-analysis ↗, licensed under Apache 2.0 ↗. Reproduced here unmodified. 
AnalysisType: rule
Filename: aws_sts_getsessiontoken_misuse.py
RuleID: "AWS.STS.GetSessionToken.Misuse"
DisplayName: "AWS STS GetSessionToken by IAM User"
Enabled: true
LogTypes:
  - AWS.CloudTrail
Tags:
  - AWS
  - AWS STS
  - Lateral Movement:Use Alternate Authentication Material
  - Privilege Escalation:Abuse Elevation Control Mechanism
Reports:
  MITRE ATT&CK:
    - TA0008:T1550.001
    - TA0004:T1548
Status: Experimental
Severity: Low
Description: >
  Detects an IAM user calling STS GetSessionToken to obtain temporary credentials.
  Attackers who have compromised long-term IAM credentials may use GetSessionToken
  to generate short-lived session tokens for lateral movement or to bypass IP-based
  policies that apply only to long-term credentials.
Runbook: |
  1. Query CloudTrail for all API calls by userIdentity:arn in the 6 hours before and after this alert to establish what the session token was used for
  2. Check if sourceIPAddress is associated with known corporate network ranges, VPN endpoints, or cloud provider IP ranges
  3. Find other alerts for this userIdentity:userName in the past 30 days to determine if GetSessionToken usage is part of normal workflow
Reference: https://docs.aws.amazon.com/STS/latest/APIReference/API_GetSessionToken.html
SummaryAttributes:
  - userAgent
  - sourceIpAddress
  - recipientAccountId
  - p_any_aws_arns
DedupPeriodMinutes: 60
Threshold: 1
Tests:
  - Name: GetSessionToken by IAM User
    ExpectedResult: true
    Log:
      {
        "awsRegion": "us-east-1",
        "eventID": "abc-123",
        "eventName": "GetSessionToken",
        "eventSource": "sts.amazonaws.com",
        "eventTime": "2024-01-15T10:30:00Z",
        "eventType": "AwsApiCall",
        "eventVersion": "1.08",
        "recipientAccountId": "123456789012",
        "requestID": "req-123",
        "sourceIPAddress": "203.0.113.50",
        "userAgent": "aws-cli/2.15.0",
        "userIdentity": {
          "accessKeyId": "AKIAIOSFODNN7EXAMPLE",
          "accountId": "123456789012",
          "arn": "arn:aws:iam::123456789012:user/example-user",
          "principalId": "AIDACKCEVSQ6C2EXAMPLE",
          "type": "IAMUser",
          "userName": "example-user"
        }
      }
  - Name: GetSessionToken Failed
    ExpectedResult: false
    Log:
      {
        "awsRegion": "us-east-1",
        "errorCode": "AccessDenied",
        "eventName": "GetSessionToken",
        "eventSource": "sts.amazonaws.com",
        "eventTime": "2024-01-15T10:30:00Z",
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
        "sourceIPAddress": "203.0.113.50",
        "userIdentity": {
          "type": "IAMUser",
          "userName": "example-user"
        }
      }
  - Name: GetSessionToken by Assumed Role
    ExpectedResult: false
    Log:
      {
        "awsRegion": "us-east-1",
        "eventName": "GetSessionToken",
        "eventSource": "sts.amazonaws.com",
        "eventTime": "2024-01-15T10:30:00Z",
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
        "sourceIPAddress": "10.0.0.1",
        "userIdentity": {
          "type": "AssumedRole",
          "arn": "arn:aws:sts::123456789012:assumed-role/MyRole/session"
        }
      }
  - Name: Unrelated STS Event
    ExpectedResult: false
    Log:
      {
        "awsRegion": "us-east-1",
        "eventName": "AssumeRole",
        "eventSource": "sts.amazonaws.com",
        "eventTime": "2024-01-15T10:30:00Z",
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
        "sourceIPAddress": "10.0.0.1",
        "userIdentity": {
          "type": "IAMUser",
          "userName": "example-user"
        }
      }


# ------ paired body: aws_sts_getsessiontoken_misuse.py ------

from panther_aws_helpers import aws_cloudtrail_success, aws_rule_context


def rule(event):
    if not aws_cloudtrail_success(event):
        return False
    return (
        event.get("eventSource") == "sts.amazonaws.com"
        and event.get("eventName") == "GetSessionToken"
        and event.deep_get("userIdentity", "type") == "IAMUser"
    )


def title(event):
    user = event.deep_get("userIdentity", "userName", default="<unknown>")
    account = event.get("recipientAccountId", "<unknown>")
    return f"IAM user [{user}] called GetSessionToken in account [{account}]"


def alert_context(event):
    return aws_rule_context(event)

Detection rules belong to the projects that publish them and remain under their own licenses. This site indexes and links to them; it claims no rights in them.