Langflow: Unauthenticated file upload leads to DoS (space exhaustion) and information leak
Description
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: `python @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: ``bash curl 'http://localhost:7860/api/v1/upload/<any_uuid>' -F "file=@<any_file>" ``
Example: ``bash # 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.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Affected products
2- Range: <1.9.1
Patches
Vulnerability mechanics
Root cause
"Missing authentication and missing file-size limits on the deprecated `POST /api/v1/upload/{flow_id}` endpoint allow unauthenticated arbitrary file uploads."
Attack vector
An unauthenticated attacker with network access to a Langflow server can send a POST request to `/api/v1/upload/<any_uuid>` with an arbitrary file attached. Because the endpoint has no authentication ([CWE-306]) and no size limit ([CWE-400]), the attacker can repeatedly upload large files to exhaust disk space, causing a denial-of-service. Additionally, the response leaks the absolute server-side path of the uploaded file ([CWE-200]), which aids in chaining further attacks. [ref_id=2]
Affected code
The vulnerable endpoint is `POST /api/v1/upload/{flow_id}` in `langflow/api/v1/endpoints.py` at the `create_upload_file` function. The route is marked `deprecated=True` but remains live in production, and unlike other endpoints it lacks any authentication or authorization check. The `flow_id` parameter is not validated, and the file is saved directly to the local filesystem via `save_uploaded_file` without a size limit. [ref_id=1] [ref_id=2]
What the fix does
The fix reuses the existing `get_flow` dependency from `api/v1/files.py`, which enforces authentication via `CurrentActiveUser` and authorization via a flow-ownership check (returning 404 for missing or cross-user flows). It also adds enforcement of the `max_file_size_upload` configuration value, returning HTTP 413 when the file exceeds the limit. These changes close the unauthenticated upload vector and prevent disk exhaustion even by authenticated users. [ref_id=1]
Preconditions
- networkNetwork access to the Langflow server's HTTP API
- authNo authentication or prior knowledge required
Generated on Jun 17, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
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