Summary
CloudFormation allows the use of Lambda-backed resource providers,
wherein Lambda can be used to write custom provisioning logic to be
executed during CloudFormation stack operations. The aforementioned
Lambda functions were executed in an AWS-managed account (thus
effectively allowing arbitrary code execution in that account),
and were passed a set of credentials ("platformCredentials") for a
role in this account that had several EventBridge permissions.
These were sufficient for an attacker to create new rules in the AWS-managed
account that leaked credentials belonging to other users of resource
providers. For example, creating a rule that matched events with
{"detail-type": ["AWS API Call via CloudTrail"]} exposed records
of other tenants' API calls, which included copies of credentials
for roles in other tenants' accounts.
Affected Services
CloudFormation
Remediation
None required
Tracked CVEs
No tracked CVEs
References
Contributed by https://github.com/korniko98
Entry Status
Finalized
Disclosure Date
Tue, Jan 21st, 2020
Exploitablity Period
-
Known ITW Exploitation
-
Detection Methods
-
Piercing Index Rating
-
Discovered by
Aidan Steele
