CVE-2026-48797: Backpropagate Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-f65r-h4g3-3h9h",
  "modified" : "2026-06-26T20:34:29Z",
  "published" : "2026-06-26T20:34:29Z",
  "aliases" : [ "CVE-2026-48797" ],
  "summary" : "Backpropagate: backprop ui --auth and backprop ui --share do not enforce authentication",
  "details" : "## Summary\n\nIn `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.\n\nThe CLI accepts two operator-facing flags intended as security controls:\n\n- `--auth user:pass` — documented as \"require HTTP Basic authentication on every request to the UI.\"\n- `--share` — documented as \"expose the UI on a public address; requires `--auth`.\"\n\nWhen `--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.\n\n**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.\n\nAn 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.\n\nThis advisory is filed primarily because the runtime contradicted an operator-facing security claim. Code-only bugs of comparable shape (auth check missing entirely from a path) would already warrant disclosure; the additional false-promise dimension raises the severity.\n\n## Impact\n\nAn attacker who reaches the bound port can:\n\n- **Read uploaded datasets** rendered in the UI preview, including content of any JSONL/CSV/TXT file the legitimate operator has uploaded for fine-tuning.\n- **Trigger arbitrary training runs** against any base model the operator has installed locally or that can be downloaded from HuggingFace.\n- **Trigger HuggingFace Hub pushes** to repositories named via the UI input (subject to the operator's local HF token's scope — typically all repos owned by the operator).\n- **Cause disk-fill DoS** via the `rx.upload` endpoint (no size cap, no extension filter, no per-session count cap in v1.1.0 / v1.1.1).\n- **Read model paths** (`source_model_path`, `dataset_path`, `model`, `uploaded_path`) which are user-supplied and bypass the `safe_path()` helper that lives in `backpropagate/ui_security.py` (path validation is dead code on the Reflex surface in v1.1.0 / v1.1.1).\n\nThe combination of unauthenticated training control, HF push target spoofing, and path-input traversal makes the affected endpoint suitable for both data exfiltration (reading uploaded training data) and supply-chain attacks (pushing tampered model weights to the operator's HF account).\n\nThe local-only default (no `--share`) reduces exposure to a host-local attacker. The `--share` flag is documented as a \"public URL\" feature; operators who used `--share --auth user:pass` had no warning that the auth half was inert.\n\n## Patches\n\nFixed in **v1.2.0** (released 2026-05-23). The patch implements real ASGI middleware via `rx.App(api_transformer=basic_auth_transformer)` that gates HTTP routes AND the `/_event` WebSocket upgrade. Four modes (`no_auth_local_only` / `token_auto` / `explicit_creds` / `production`), HMAC-signed cookie validated PRE-`websocket.accept()`, Host + Origin allowlists. The middleware ships alongside a 4-layer defense in depth at the cli.py / ui_app/app.py / rxconfig.py / env-strip surfaces so direct `python -m reflex run` invocations (bypassing the CLI guard) also enforce authentication.\n\nUpgrade with:\n\n- pip: `pip install --upgrade backpropagate`\n- npm: `npm install -g @mcptoolshop/backpropagate@latest`\n\nFull release notes: https://github.com/mcp-tool-shop-org/backpropagate/blob/main/CHANGELOG.md#120---2026-05-23\n\n## Workarounds\n\nIf users cannot upgrade immediately:\n\n1. **Do not pass `--auth` or `--share` to `backprop ui`.** Run the UI with no flags (`backprop ui`); it will bind to `localhost` and accept any client that can reach `127.0.0.1`.\n2. **For remote access, use SSH port-forwarding** instead of `--share`:\n   ```\n   # On the client:\n   ssh -L 7860:localhost:7860 <training-host>\n   # On the server:\n   backprop ui            # no --share\n   # Then open http://localhost:7860 in your local browser.\n   ```\n   SSH provides the authentication layer the Reflex UI did not.\n3. **Audit existing deployments.** If any host running `backpropagate >= 1.1.0` has previously been launched with `--share`, treat any uploaded training data, model paths, or HF push targets visible in that UI session as potentially exposed. Re-issue HF tokens that have been in use during such sessions.\n\n**Binary distribution gap.** Standalone binaries (Windows .exe / macOS .app via PyInstaller) failed to build for v1.2.0 and will land in a follow-up patch release. In the interim, users who relied on the v1.1.x binary distribution should install the patched version via `pip install backpropagate==1.2.0` to receive the auth-bypass fix. The v1.2.0 PyPI package and `@mcptoolshop/backpropagate@1.2.0` npm package both carry the patched code.\n\n## Credit\n\nDiscovered by the dogfood-swarm Stage A audit on 2026-05-22 (finding ID `FRONTEND-A-001`, classified CRITICAL). The audit also surfaced contradicting documentation in CHANGELOG / SHIP_GATE / README; those were corrected in v1.2.0 alongside the runtime fix.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "backpropagate"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.1.0"
      }, {
        "fixed" : "1.2.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "@mcptoolshop/backpropagate"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "1.1.0"
      }, {
        "fixed" : "1.2.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/mcp-tool-shop-org/backpropagate/security/advisories/GHSA-f65r-h4g3-3h9h"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-48797"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mcp-tool-shop-org/backpropagate"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mcp-tool-shop-org/backpropagate/releases/tag/v1.2.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1295", "CWE-358", "CWE-862" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-26T20:34:29Z",
    "nvd_published_at" : "2026-06-17T13:20:43Z"
  }
}