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.