CVE-2026-49859 Deno: `fetch()` API sandbox bypass via missing DNS resolution check

What is CVE-2026-49859?

CVE-2026-49859 is a medium-severity server-side request forgery vulnerability in denoland deno, published on 23 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.8.1, when fetch() was called, Deno checked the destination hostname against --deny-net rules but did not re-check the IP addresses that hostname resolved to. An attacker-controlled script could use a specially crafted domain name that passes the hostname check yet resolves to a denied IP, bypassing the network restriction entirely. This vulnerability is fixed in 2.8.1.

Weakness: CWE-918, CWE-693

Which versions are affected by CVE-2026-49859?

2 open source packages ship an affected version, including deno. It affects 1 product.

Products include Deno Deno.

How do I fix CVE-2026-49859?

Upgrade deno to 2.8.1 or later.

Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.

Is CVE-2026-49859 being exploited?

There is no known exploitation of CVE-2026-49859 in the wild and no public exploit code.

Other vulnerabilities in denoland deno

• CVE-2023-28445 Deno improperly handles resizable ArrayBuffer Critical 10.0
• CVE-2022-24783 Sandbox bypass leading to arbitrary code execution in Deno Critical 10.0
• CVE-2021-32619 Static imports inside dynamically imported modules do not adhere to permission checks Critical 9.8
• CVE-2026-22863 Deno node:crypto doesn't finalize cipher Critical 9.2
• CVE-2024-27936 Deno interactive permission prompt spoofing via improper ANSI stripping High 8.8

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-cpgj-f7g3-2pp2, JLSEC-2026-1164.