LocalStack version 4.9.2 contains a flaw that permits arbitrary code execution when an attacker supplies a crafted URL to the templateURL parameter of the _localstack/cloudformation/deploy endpoint. The content fetched from the externally hosted URL is executed within the Docker container that runs LocalStack, allowing the attacker to run arbitrary commands in that container’s context. This vulnerability does not rely on user interaction beyond providing the templateURL; it can be used by any entity capable of issuing requests to the vulnerable endpoint.

The vulnerability affects the LocalStack product, specifically the 4.9.2 release. Systems that run this version of LocalStack and expose the cloudformation deploy endpoint to potential attackers are at risk. No other vendors or product versions are currently known to be affected.

The issue provides a clear remote code execution path. The CVSS score is 9.6, indicating critical severity, and the EPSS score is <1%. The potential impact remains severe, allowing full compromise of the container environment. The vulnerability is not listed in CISA’s KEV catalog, but its exploitation would likely be straightforward for an attacker who can reach the interface. The vulnerability can be exploited remotely by supplying a malicious URL to the templateURL field, causing the container to execute the attacker’s payload without further authentication or privilege escalation within the LocalStack process.