AWS Identity Crisis: When Cached Credentials Become a Cloud Skeleton Key

From a SOC perspective, we rely heavily on CloudTrail anomaly detection. If we see API calls originating from a developer workstation IP that don't match the usual behavior patterns, we trigger an alarm.

However, prevention is better. We enforce the use of aws-vault or the credential_process feature in the AWS config file. This keeps the temporary credentials in memory (Windows Credential Manager) rather than a static clear-text file on disk. It makes it much harder for a standard file-scanning malware to exfiltrate the keys.

This is exactly why I tell clients to stop assigning long-term access keys to humans entirely. Use Identity Center (SSO) for everything interactive.

If you must cache keys for automation scripts on endpoints, ensure you use strict IAM policies scoping down to specific buckets or services. Also, consider this KQL query for hunting in your SIEM to spot suspicious aws cli usage patterns:

DeviceProcessEvents
| where ProcessVersionInfoOriginalFileName == "aws.exe"
| where ProcessCommandLine contains "s3 cp" or ProcessCommandLine contains "describe-instances"

I feel your pain. We dealt with this recently. The fix for us was aggressive session timeouts via the SSO configuration. We reduced the session duration to 1 hour for developer roles.

While annoying for them, it significantly reduces the window where a cached key is valid. We also deployed a logon script that runs:

rm -rf ~/.aws/credentials
rm -rf ~/.aws/config


It forces them to re-authenticate via SSO every reboot, ensuring no stale tokens linger.

While timeouts help, auditing for existing stale caches is crucial for immediate triage. You should run a quick scan across your Windows endpoints to locate where these keys are persisting. This PowerShell snippet helps identify AWS credential files lying around in user directories:

Get-ChildItem -Path C:\Users\ -Recurse -Filter "credentials" -Include "*" -ErrorAction SilentlyContinue | Select-String -Pattern "aws_access_key_id"

This gives you a starting point for cleanup.

To build on the auditing point, automated credential rotation at the endpoint level is often overlooked. We’ve implemented a scheduled task via GPO that runs daily to scrub the credentials file. This ensures that even if a user forgets, the stale key is removed from the disk. You can automate this with a quick PowerShell check:

$credFile = "$env:USERPROFILE\.aws\credentials"
if (Test-Path $credFile) {
    if ((Get-Item $credFile).LastWriteTime -lt (Get-Date).AddHours(-12)) {
        Clear-Content $credFile
    }
}