Impact

This is a cross-account impersonation vulnerability in the auth-aws
plugin. The vulnerability allows an IAM role from an untrusted AWS account to
authenticate by impersonating a role with the same name in a trusted account,
leading to unauthorized access.

This impacts all users of the auth-aws plugin who operate in a multi-account AWS
environment where IAM role names may not be unique across accounts.

The core of the vulnerability is a flawed caching mechanism that fails to
validate the AWS Account ID during authentication. While the use of wildcards in
a bound_iam_principal_arn configuration significantly increases the attack
surface, wildcards are not a prerequisite for exploitation. The vulnerability
can be exploited with specific ARN bindings if a role name collision occurs.

Successful exploitation can lead to unauthorized access to secrets, data
exfiltration, and privilege escalation. Given that the only prerequisite is a
duplicate role name, the severity is considered high.

Patches

This vulnerability has been patched in version 0.1.1 of the auth-aws plugin.
Users are advised to upgrade to version 0.1.1 or later to remediate this vulnerability.

Workarounds

For users who are unable to upgrade to version 0.1.1 immediately, the most effective
workaround is to guarantee that IAM role names are unique
across all AWS accounts that could potentially interact with your OpenBao
environment. This is the most critical mitigation step.

Primary Mitigation: Audit your AWS organizations to identify and rename any
duplicate IAM role names. Enforce a naming convention that includes
account-specific identifiers to prevent future collisions.

While removing wildcards from your bound_iam_principal_arn configuration is
still recommended as a security best practice, it will not mitigate this
vulnerability if duplicate role names exist.

References

This vulnerability was discovered and reported by Pavlos Karakalidis