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

June 16, 2026 (updated July 20, 2026)

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.

References

github.com/advisories/GHSA-83pc-3rw9-qpwj
github.com/denoland/deno/security/advisories/GHSA-83pc-3rw9-qpwj
nvd.nist.gov/vuln/detail/CVE-2026-49860

Code Behaviors & Features

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