CVE-2025-65200: From Reflected XSS to Container RCE in LocalStack via CloudFormation Deploy UI
What is LocalStack and how to quickly start it? LocalStack is a popular open-source platform that emulates AWS services locally, allowing developers to build and test cloud infrastructure without touching real AWS accounts.
Because LocalStack runs on localhost and is marketed as a development-only tool, its security surface is often underestimated. During a short exploration of LocalStack’s CloudFormation features, I discovered a broken deployment UI that led to a reflected XSS vulnerability.
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