GHSA-vwmf-pq79-vjvx

Описание

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

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

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.)

Step 2: Exploit -- Unauthenticated RCE

Step 3: Verify Code Execution

Actual Test Results

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

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:

In generate_flow_events → create_graph(), only the build_graph_from_db path should be reachable for unauthenticated requests: