CVE-2026-49983: Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.8.1, environment access is gated by the env permission. You can deny it with --d...

Description

Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.8.1, 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. This vulnerability is fixed in 2.8.1.

Metrics

CVSS 3.1

5.2/10

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

EPSS Probability

0.10%

1.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-863

References

https://github.com/denoland/deno/security/advisories/GHSA-4c8g-jvcx-v4hv

Timeline

Published: Jun 23, 2026
Last Modified: Jun 23, 2026
Status: Undergoing Analysis

Frequently Asked Questions

What is CVE-2026-49983?

Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.8.1, 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. This vulnerability is fixed in 2.8.1.

How severe is CVE-2026-49983?

CVE-2026-49983 has a CVSS score of 5.2/10 (MEDIUM severity). The EPSS model estimates a 0.10% probability of exploitation in the next 30 days.

How do I fix CVE-2026-49983?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.