AI analysis
Claude Opus · 8 Nov 2026, 10:19 CET
Trusted Remote Execution example SSM script allows root command injection on instances
An example provisioning script in Trusted Remote Execution (REX) before 2026-07-28 created Rex-RO and Rex-RW SSM documents that let authorised invokers run commands as root, bypassing Cedar policies. Delete any documents created from that script in every account and Region.
In plain terms
Trusted Remote Execution (REX) is a tool for running controlled administrative actions on cloud servers managed through AWS Systems Manager (SSM). Access to those actions is meant to be restricted by Cedar policies, a rules language that defines who may do what. REX shipped an example script that sets up two SSM documents, Rex-RO and Rex-RW. An SSM document is a predefined set of instructions that Systems Manager runs on a server. The documents created by versions of that script before 2026-07-28 contain a flaw called command injection. Command injection means text supplied by a user ends up being run as an operating system command.
As a result, someone who is allowed to use these documents could run any command they like as root, the all-powerful administrator account, on the managed server. This would ignore the Cedar rules that were supposed to limit them. Teams that deployed REX using the example script should check every AWS account and Region where they ran it.