Guardrails AI is a Python framework that helps build AI applications. On May 11, 2026 at approximately 6:00 PM Pacific, an attacker published a malicious version of `guardrails-ai` (0.10.1) to PyPI. Aany user who installed `guardrails-ai==0.10.1` from PyPI on May 11, 2026 may be affected. Security researchers identified the malicious package within approximately 2 hours of publication, and PyPI quarantined the repository. Based on our telemetry, Guardrails AI maintainers have observed no requests to Guardrails AI infrastructure originating from the malicious 0.10.1 version, and a review of system and access logs has produced no evidence of user data exfiltration through their systems. Users should upgrade to version 0.10.2 or downgrade to version 0.10.0, both of which are unaffected. Those who installed version 0.10.1 should rotate any credentials accessible from their machine (GitHub PATs, cloud provider keys, package registry tokens, API keys) and audit their GitHub account for unauthorized workflows or repositories.

An arbitrary code execution vulnerability exists in versions 0.2.9 up to 0.5.10 of the Guardrails AI Guardrails framework because of the way it validates XML files. If a victim user loads a maliciously crafted XML file containing Python code, the code will be passed to an eval function, causing it to execute on the user's machine.

RAIL documents are an XML-based format invented by Guardrails AI to enforce formatting checks on LLM outputs. Guardrails users that consume RAIL documents from external sources are vulnerable to XXE, which may cause leakage of internal file data via the SYSTEM entity.