GHSA-q4pp-j36h-3gqg

Опубликовано: 24 авг. 2023

Источник: github

Github: Прошло ревью

Описание

Minimal basti IAM Policy Allows Shell Access

Summary

The provided Minimal IAM Policy for bastic connect does not include ssm:SessionDocumentAccessCheck. This results in the ability to get a shell session on the bastion, not just the intended access for Port Forwarding.

Details

basti connect is designed to "securely connect to your RDS/Aurora/Elasticache/EC2 instances", using a bastion instance "with AWS Session Manager port forwarding capability to make the target available on your localhost."

The Minimal IAM Policy allows port forwarding via the following statement:

{ "Effect": "Allow", "Action": "ssm:StartSession", "Resource": [ "arn:aws:ssm:*:*:document/AWS-StartPortForwardingSessionToRemoteHost", "arn:aws:ec2:<your-region>:<your-account-id>:instance/<your-basti-instance-id>" ] }

This statement does not include the following condition:

"Condition": { "BoolIfExists": { "ssm:SessionDocumentAccessCheck": "true" } }

As a result, the basti connect minimal policy is logically identical to:

{ "Effect": "Allow", "Action": "ssm:StartSession", "Resource": [ "arn:aws:ssm:*:*:document/AWS-StartPortForwardingSessionToRemoteHost", "arn:aws:ssm:*:*:document/SSM-SessionManagerRunShell", "arn:aws:ec2:<your-region>:<your-account-id>:instance/<your-basti-instance-id>" ] }

A basti admin would expect users under the minimal policy to be able to port forward. However, they could also get a shell on the bastion.

For more details on this footgun, see: https://ramimac.me/ssm-iam

PoC

Complete instructions, including specific configuration details, to reproduce the vulnerability.

Impact

Impact would depend on configuration/hardening of the bastion. I've seen examples where bastions have credentials to downstream systems in configuration or memory that would be exposed.

Ссылки

Пакеты

Наименование

basti-cdk

npm

Затронутые версииВерсия исправления

< 1.0.1

1.0.1