Langflow has Authenticated Cross-Project File Disclosure via Unscoped MCP Resource Handlers

Summary

Langflow's project-scoped MCP transport authenticates the caller for the project_id in the connection URL, but the subsequent resources/read operation does not authorize the resource URI being requested. An authenticated user can connect to their own project-scoped MCP endpoint and supply a crafted file-download URI that points to another user's flow-backed file. The server then reads and returns the victim file without verifying ownership or project membership.

This is a cross-user authorization bypass (userA -> userB) that allows arbitrary read access to files stored under other users' flow namespaces.

Details

Verified against local checkout:

• Repository: langflow-ai/langflow
• Verified on release tag: v1.8.3
• Commit: 08bf98404cfd7737fde57a2588785766cdf1b42e
• Earliest stable release known to contain the vulnerable code path: v1.6.8

Relevant code path:

1. src/backend/base/langflow/api/v1/mcp_projects.py:147-193 verify_project_auth_conditional() authenticates the caller and checks access only to the project_id in the MCP transport URL.

2. src/backend/base/langflow/api/v1/mcp_projects.py:1238-1241 The project-scoped MCP server registers read_resource() and forwards the attacker-controlled URI directly to handle_read_resource(uri=uri).

3. src/backend/base/langflow/api/v1/mcp_utils.py:163-182 handle_read_resource() parses the last two URI path segments as flow_id and filename, then directly calls:

   storage_service.get_file(flow_id=flow_id, file_name=filename)
   

   No check ties the supplied flow_id back to the authenticated user or the current project.

4. src/backend/base/langflow/services/storage/local.py:141-149 src/backend/base/langflow/services/storage/s3.py:200-217 The storage layer performs a raw namespace read and is not authorization-aware.

The result is that authorization is enforced at MCP connection time, but not at resource-read time. Once an attacker has access to any project-scoped MCP endpoint they own, they can read another user's flow-backed file by passing a victim-controlled URI.

This issue is also easier to exploit because the global MCP helpers expose cross-user discovery data:

• src/backend/base/langflow/api/v1/mcp_utils.py:102-121 handle_list_resources(project_id=None) lists files for all flows.
• src/backend/base/langflow/api/v1/mcp_utils.py:333-380 handle_list_tools(project_id=None) queries all flows and includes flow IDs in tool metadata.

That global enumeration is not required for exploitation, but it makes obtaining victim identifiers much easier.

PoC

Preconditions:

• Langflow is running locally with authentication enabled.
• Two separate users exist on the same instance.
• The victim has a flow with an uploaded file.
• The attacker has access to any project they own.

Verify the issue locally by starting Langflow with:

cd '/Users/r1zzg0d/Documents/CVE hunting/targets/langflow'

set -a
source .env.verify
set +a

export LANGFLOW_CONFIG_DIR="$PWD/.langflow-verify"

uv run python - = 1.6.8,