Backpropagate is a Python library for fine-tuning large language models on a single GPU. In versions 1.1.0 and 1.1.1, the optional Reflex web UI exposes a training control plane without authentication: dataset upload, model load, training start/stop, multi-run orchestration, GGUF export, and HuggingFace Hub push. The CLI accepts two operator-facing flags intended as security controls: --auth user:pass — documented as "require HTTP Basic authentication on every request to the UI." and--share — documented as "expose the UI on a public address; requires --auth." When --auth user:pass is passed, the CLI prints Auth: enabled (user: <username>) to confirm to the operator that authentication is active, then exports BACKPROPAGATE_UI_AUTH=user:pass to the subprocess that launches the Reflex backend. The Reflex backend (backpropagate/ui_app/**) never reads BACKPROPAGATE_UI_AUTH. No authentication middleware is registered. No request-level guard runs. No WebSocket upgrade guard runs. Any client that reaches the bound port — local or remote, depending on whether --share is used — has full UI access. An inline comment at backpropagate/cli.py:1217-1218 in the v1.1.0 source documents the gap: "For Phase 1 the variable is exported but Reflex doesn't read it yet." This comment was internal-facing; the user-facing documentation (README, CHANGELOG, SHIP_GATE) advertised the contract as enforced. An attacker who reaches the bound port can read uploaded datasets, trigger arbitrary training runs…

Affected: PyPI: backpropagate, npm: @mcptoolshop/backpropagate

## Summary

In `backpropagate >= 1.1.0`, the optional Reflex web UI (`pip install backpropagate[ui]`, launched via `backprop ui`) exposes a training control plane: dataset upload, model load, training start/stop, multi-run orchestration, GGUF export, and HuggingFace Hub push.

The CLI accepts two operator-facing flags intended as security controls:

- `--auth user:pass` — documented as "require HTTP Basic authentication on every request to the UI." - `--share` — documented as "expose the UI on a public address; requires `--auth`."

When `--auth user:pass` is passed, the CLI prints `Auth: enabled (user: <username>)` to confirm to the operator that authentication is active, then exports `BACKPROPAGATE_UI_AUTH=user:pass` to the subprocess that launches the Reflex backend.

**The Reflex backend (`backpropagate/ui_app/**`) never reads `BACKPROPAGATE_UI_AUTH`.** No authentication middleware is registered. No request-level guard runs. No WebSocket upgrade guard runs. Any client that reaches the bound port — local or remote, depending on whether `--share` is used — has full UI access.

An inline comment at `backpropagate/cli.py:1217-1218` in the v1.1.0 source documents the gap: *"For Phase 1 the variable is exported but Reflex doesn't read it yet."* This comment was internal-facing; the user-facing documentation (README, CHANGELOG, SHIP_GATE) advertised the contract as enforced.

This advisory is filed primarily because the runtime contradicted an operator-facing security claim. Cod…

Affected: PyPI: backpropagate

## Summary

In `backpropagate >= 1.1.0`, the optional Reflex web UI (`pip install backpropagate[ui]`, launched via `backprop ui`) exposes a training control plane: dataset upload, model load, training start/stop, multi-run orchestration, GGUF export, and HuggingFace Hub push.

The CLI accepts two operator-facing flags intended as security controls:

- `--auth user:pass` — documented as "require HTTP Basic authentication on every request to the UI." - `--share` — documented as "expose the UI on a public address; requires `--auth`."

When `--auth user:pass` is passed, the CLI prints `Auth: enabled (user: <username>)` to confirm to the operator that authentication is active, then exports `BACKPROPAGATE_UI_AUTH=user:pass` to the subprocess that launches the Reflex backend.

**The Reflex backend (`backpropagate/ui_app/**`) never reads `BACKPROPAGATE_UI_AUTH`.** No authentication middleware is registered. No request-level guard runs. No WebSocket upgrade guard runs. Any client that reaches the bound port — local or remote, depending on whether `--share` is used — has full UI access.

An inline comment at `backpropagate/cli.py:1217-1218` in the v1.1.0 source documents the gap: *"For Phase 1 the variable is exported but Reflex doesn't read it yet."* This comment was internal-facing; the user-facing documentation (README, CHANGELOG, SHIP_GATE) advertised the contract as enforced.

This advisory is filed primarily because the runtime contradicted an operator-facing security claim. Cod…