CVE-2026-55450: Langflow: Unauthenticated file upload leads to DoS (space exhaustion) and information leak

Summary

Unauthenticated users can upload any amount of data to the server without any limitations. No need for any prior knowledge, only network access to Langflow.

This can lead to space exhaustion on the server.

In adition, in the response, the absolute path of the uploaded file is reported to the attacker, which is an information leak that can assist in chaining other primitives.

Tested on commit 2d67402b1dbaefcbce85a244d4a6cd5e4bda1cfe

Details

Code is in langflow/api/v1/[endpoints.py](http://endpoints.py/):

@router.post(
    "/upload/{flow_id}",
    status_code=HTTPStatus.CREATED,
    deprecated=True,
)
async def create_upload_file(
    file: UploadFile,
    flow_id: UUID,
) -> UploadFileResponse:
...

As can be seen above, there is no authentication. There is not validation over flow_id as well, unlike other endpoints:

        flow_id_str = str(flow_id)
        file_path = await asyncio.to_thread(save_uploaded_file, file, folder_name=flow_id_str)

Function save_uploaded_file saves the file to local file-system. Suggested fix:

1. Add authentication to route.
2. Only return relative path or filename.

PoC

PoC:

curl 'http://localhost:7860/api/v1/upload/<any_uuid>' -F "file=@<any_file>"

Example:

# curl 'http://localhost:7860/api/v1/upload/11111111-1111-1111-1111-111111111111' -F "file=@/tmp/dummy.txt"
{"flowId":"11111111-1111-1111-1111-111111111111","file_path":"/Users/ori/Library/Caches/langflow/11111111-1111-1111-1111-111111111111/9d63c3b5b7623d1fa3dc7fd1547313b9546c6d0fbbb6773a420613b7a17995c8.txt"}

Impact

1. Space exhaustion on server that can lead to Denial-of-Service.
2. Information leak - leakage of absolute path of langflow's cache directory in server.

Patches

Fixed in 1.9.1 via PR #12831. The deprecated POST /api/v1/upload/{flow_id} endpoint now uses the get_flow dependency, requiring an authenticated user and flow ownership (returns 404 for missing or cross-user flows), and enforces the max_file_size_upload limit (HTTP 413) — closing the unauthenticated upload and disk-exhaustion vectors. Upgrade to 1.9.1 or later.

Note: the response still returns the file's absolute path (file_path); after this fix it is only disclosed to the authenticated owner of the flow.

Ori Lahav Security Researcher @ Rubrik Inc.