Vulnerability · Published Jun 23, 2026 · Assigned by GitHub_M

CVE-2026-49860Deno: WebSocket API sandbox bypass via missing post-DNS check

Medium 5.2

In plain English

A medium-severity server-side request forgery in deno from denoland. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.1% (higher than 3% of all known vulnerabilities).

Severity (CVSS 3.1)5.2Medium

Exploit odds (30 days)0.1%top 96.5% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.8.1, when a WebSocket connection was opened, 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.

Affected products (as reported)

Vendor	Product	Versions
denoland	deno	< 2.8.1

Weakness: CWE-918 · Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

References

https://github.com/denoland/deno/security/advisories/GHSA-83pc-3rw9-qpwj x_refsource_CONFIRM