Deno: process.loadEnvFile() bypasses env permission checks and mutates process.env with only read access

Summary

In Deno, environment access is gated by the env permission. You can deny it with --deny-env, or restrict it to a specific allowlist with --allow-env=FOO,BAR. The expectation is that a program running without env permission cannot change process.env.

process.loadEnvFile() (the Node-compatible API for loading variables from a .env file) does not honor this. It only checks that the program has read permission for the dotenv file, then writes every key in that file into the process environment — even when env access is denied.

In effect, --allow-read plus a writable or attacker-controlled .env file is enough to defeat --deny-env.

Am I affected?

You are potentially affected if all of the following are true:

1. You run Deno v2.3.0 or newer.
2. Your program (or any dependency it imports) calls process.loadEnvFile() from node:process.
3. You rely on Deno's permission model — specifically --deny-env, an --allow-env=… allowlist, or running without granting env — as a security boundary.
4. The .env path passed to loadEnvFile() can be controlled or modified by a less-trusted party (untrusted input, user-writable directory, third-party dependency, etc.) and is covered by your --allow-read grant.

If your program does not use process.loadEnvFile() at all, or if it already grants full env access, this advisory does not change your risk.