GHSA-95g5-m242-wvhr · Infrastructure
NO FIX YET · SEE WHAT TO DO
The Trusted Remote Execution setup guide included an example script that created SSM documents Rex-RO and Rex-RW with an OS command injection flaw in how input parameters were handled. A user allowed to invoke those SSM documents can supply crafted input to run unintended OS commands on the managed instance, outside the REX sandbox.
first public Nov 6, 2026 · 1 source
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Only teams that created the Rex-RO or Rex-RW SSM documents by following the Trusted Remote Execution setup guide are affected; the shipped REX artifact is not. A user with permission to invoke those documents could inject OS commands on managed instances. Teams that never ran the example can skip it.
Not affected if no-rex-ssm-documents, shipped-rex-only
Who cares aws, lab-disclosure, managed-instances, rex, ssm
Rex-RO or Rex-RW exist in each account and region where the example was run, for example with aws ssm list-documents.Rex-RO and Rex-RW SSM documents created from it, in each account and region where the example ran.CVE-2026-122193 - Issue with Trusted Remote Execution Setup Guide - OS command injection in the example SSM documents in Trusted Remote Execution (REX)
Bulletin ID: 2026-173-AWS Scope: AWS Content Type: Important (requires attention) Publication Date: 11/06/2026 09:00 AM PST
Description:
Trusted Remote Execution (REX) is an open-source framework for executing sandboxed scripts on managed instances, where a signed Cedar policy is meant to be the immutable security boundary around each script run.
We identified CVE-2026-122193, an OS command injection issue in an example provided in the set-up documentation. The example included a script that creates AWS Systems Manager (SSM) documents (Rex-RO and Rex-RW) for running scripts on managed instances. Due to how the example script handled input parameters, a user with permissions to invoke the SSM document could supply crafted input that would run unintended operating system commands on the managed instance, outside of the REX sandbox. The scriptArgs parameter is affected by the same class of issue.
Impacted versions:
This is not an issue in a shipped REX artifact version. It is an affected example in the set-up documentation. Anyone who created the Rex-RO / Rex-RW SSM documents by following the guide is affected.
Resolution:
We removed this set-up example from the guide. We recommend you delete any SSM documents if you created them, in each account/region where you ran the example:
Workarounds:
None.
References:
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