OS Command Injection in CodeCatalyst Blueprints SDK Exposes Local Merge Strategies

AWS has patched an operating system command injection vulnerability in its CodeCatalyst blueprints SDK. The flaw, tracked as CVE-2026-85012, allowed attackers to execute arbitrary commands during project resynthesis by manipulating the .ownership-file.

What happened

The vulnerability existed in the @amazon-codecatalyst/blueprints.blueprint npm package, an open-source framework for building project templates. According to the AWS Security Bulletin published on 09/03/2026, the blueprint resynthesis framework reads the .ownership-file to determine modifiable files. In versions before 0.3.156, the owner field of a [local] merge strategy entry was passed to an operating system command through a shell without validation. This lack of sanitisation allowed shell metacharacters to be interpreted as commands.

A user with permission to commit to a repository could place malicious characters in that field. This would execute arbitrary commands in the environment performing resynthesis, leveraging the privileges and credentials available to that environment. The issue was identified in the blueprint resynthesis framework specifically, affecting how local merge strategies are processed.

Why it matters

This flaw impacts any direct consumer of the affected npm package versions up to 0.3.155. The .ownership-file is a standard part of a project, meaning the affected merge strategy activates without additional configuration. Attackers could potentially escalate privileges or access scoped credentials within the resynthesis environment if they control the repository content.

However, AWS states that no action is required for users of the Amazon CodeCatalyst service itself. Resynthesis runs in an isolated per-project environment with scoped credentials. The service applies server-side validation that rejects [local] merge strategy commands outside a restricted allowlisted form, including for older blueprint versions. This server-side protection mitigates the risk for managed service users.

Next steps

• Upgrade the @amazon-codecatalyst/blueprints.blueprint package to version 0.3.156 or later immediately.
• Review any forked or derivative code to ensure it incorporates the new fixes from version 0.3.156.
• Audit repository permissions to ensure only trusted users can commit to projects using these blueprints.
• Verify that local development environments are not using vulnerable versions of the SDK for testing.

Detection notes

Security teams should monitor for unusual shell executions during automated build or resynthesis processes. Look for commands originating from unexpected source files like .ownership-file modifications. Check for outbound network connections from build agents that do not match standard dependency installation patterns.

Investigate any sudden changes in file permissions or unexpected process spawns within isolated build environments. Review commit histories for recent additions of shell metacharacters in configuration files. Contain affected build agents by isolating them from internal networks if suspicious activity is confirmed. Analyse logs for failed validation attempts that might indicate probing for this specific injection vector.

What to do and how to stay safe: AWS

• Audit all internal repositories for usage of @amazon-codecatalyst/blueprints.blueprint versions prior to 0.3.156.
• Implement strict input validation for any custom scripts that process .ownership-file data in local environments.
• Monitor build logs for unexpected command executions or shell metacharacter interpretation errors.
• Ensure that build environments run with minimal necessary privileges to limit the impact of any potential injection.

Step-by-step guide: Emergency Patching: How to Fix Critical Flaws Without Breaking Production

General security guidance from the Packet Tribune newsroom. It is not confirmed advice from the organisations named in this story.

Frequently asked questions

Does this vulnerability affect AWS CodeCatalyst service users?

No, AWS states that no action is required for CodeCatalyst service users due to server-side validation and isolated environments.

Which package versions are vulnerable to CVE-2026-85012?

Versions of @amazon-codecatalyst/blueprints.blueprint up to and including 0.3.155 are vulnerable.

How was the vulnerability fixed in version 0.3.156?

Version 0.3.156 removes shell interpretation of the owner field and rejects values outside an allowlisted command form.