Auth bypass in Deno
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.
Vulnerability class: Broken Access Control
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.2 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.001 (2.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 3rd percentile — 2.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.001 · newest: 0.001 · change: 0.000
Affected products
- Deno
- Denoland Deno — versions < 2.8.1
Weakness classification (CWE)
References
- github.com/denoland/deno/security/advisories/GHSA-4c8g-jvcx-v4hv (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-49983?
- CVE-2026-49983 is a medium-severity vulnerability in Deno, classified under Incorrect Authorization. CVSS score: 5.2/10. Published 2026-06-23.
- How severe is CVE-2026-49983?
- Medium severity. CVSS v3 base score is 5.2 out of 10.