{"id":"CVE-2026-49859","aliases":["GHSA-cpgj-f7g3-2pp2"],"url":"https://o3.security/vulnerability/CVE-2026-49859","summary":"Deno: `fetch()` API sandbox bypass via missing DNS resolution check","details":"## Summary\n\nWhen `fetch()` was called, Deno checked the destination hostname against\n`--deny-net` rules but did not re-check the IP addresses that hostname\nresolved to. An attacker-controlled script could use a specially crafted domain\nname that passes the hostname check yet resolves to a denied IP, bypassing the\nnetwork restriction entirely.\n\n## Impact\n\nCode running under `--deny-net` could reach hosts that the user intended to\nblock. In practice this means network isolation rules — for example, blocking\naccess to `localhost` or internal services — could be silently circumvented by\na malicious or compromised dependency.\n\nA companion advisory covers the same class of issue in the WebSocket API.\n\n## Who is affected\n\nUsers who:\n\n- run untrusted or third-party code with `deno run`, and\n- rely on `--deny-net` to restrict which hosts that code can reach.\n\nIf you do not use `--deny-net`, or if you only run fully trusted code, you are\nnot affected.\n\n## Workaround\n\nNo workaround is available short of upgrading. If upgrading immediately is not\npossible, avoid granting `--allow-net` to untrusted code that also has\n`--deny-net` restrictions you depend on for security.\n\n## Fix\n\nThe `fetch()` DNS resolver now performs a post-resolution check on every IP\naddress before passing it to the HTTP connector, consistent with how\n`Deno.connect` already behaved.","published":"2026-06-23T17:14:16.888Z","modified":"2026-10-28T02:30:26.902548051Z","cvss":{"score":5.2,"severity":"MEDIUM","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N"},"epss":{"score":0.00141,"percentile":0.03718,"asOf":"2026-09-04"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"crates.io","name":"deno","fixedVersion":"2.8.1"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/49xxx/CVE-2026-49859.json"},{"type":"ADVISORY","url":"https://github.com/denoland/deno/security/advisories/GHSA-cpgj-f7g3-2pp2"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-49859"},{"type":"PACKAGE","url":"https://github.com/denoland/deno"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:26.902548051Z"}}