CVE-2026-69258: Flowise: Unauthenticated Property Injection into Flow Execution Context via Ungated `overrideConfig` Spread in Prediction API

The POST /api/v1/prediction/:id endpoint — which is unauthenticated (whitelisted in WHITELIST_URLS) — accepts an overrideConfig object in the request body. This object is unconditionally spread into the internal flowConfig and flowData objects at two locations in the codebase without checking apiOverrideStatus. This allows an unauthenticated attacker to inject arbitrary properties into the flow execution context of any public chatflow, enabling session hijacking, cross-session data pollution, chat history manipulation, and injection of attacker-controlled values into $flow.* template variables consumed by flow nodes.

This is distinct from the previously reported overrideConfig vulnerability (GHSA-5cph-wvm9-45gj), which addressed overrideConfig’s ability to modify node input parameters via replaceInputsWithConfig(). That function is properly gated behind apiOverrideStatus. The vulnerability reported here is in two separate, ungated spread operations that were not addressed by the GHSA-5cph fix.