CVE-2026-33017: How I Found an Unauthenticated RCE in Langflow by Reading the Code They Already Fixed

A security researcher discovered CVE-2026-33017, an unauthenticated remote code execution vulnerability in Langflow, by analyzing the code that previously fixed CVE-2025-3248. While the earlier fix added authentication to a vulnerable endpoint using exec(), the researcher found the same exec() call reachable through the public flow build endpoint (/build_public_tmp), which is intentionally unauthenticated. The flaw allows attackers to supply arbitrary flow definitions via the data parameter, bypassing the intended behavior of loading saved flows from the database.