CVE-2026-41182: LangSmith SDK: Streaming token events bypass output redaction

Summary

The LangSmith SDK's output redaction controls (hideOutputs in JS, hide_outputs in Python) do not apply to streaming token events. When an LLM run produces streaming output, each chunk is recorded as a new_token event containing the raw token value. These events bypass the redaction pipeline entirely — prepareRunCreateOrUpdateInputs (JS) and _hide_run_outputs (Python) only process the inputs and outputs fields on a run, never the events array. As a result, applications relying on output redaction to prevent sensitive LLM output from being stored in LangSmith will still leak the full streamed content via run events.

Details

Both JS and Python SDKs are affected. The same pattern exists in both:

• JS SDK: traceable.ts:997-1003 and traceable.ts:1044-1050
• Python SDK: run_helpers.py:1924 and run_helpers.py:1996

In both SDKs, new_token events with raw kwargs.token values are added during streaming, and the redaction pipeline (hideOutputs in JS, hide_outputs in Python) only processes inputs/outputs — never events.