{"id":"JLSEC-2026-1164","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.","modified":"2026-08-05T18:37:02.708842313Z","published":"2026-08-05T18:20:40.259Z","upstream":["CVE-2026-49859","EUVD-2026-38541","GHSA-cpgj-f7g3-2pp2"],"database_specific":{"license":"CC-BY-4.0","sources":[{"html_url":"https://nvd.nist.gov/vuln/detail/CVE-2026-49859","database_specific":{"status":"Analyzed"},"id":"CVE-2026-49859","imported":"2026-08-05T06:30:31.265Z","modified":"2026-06-29T14:38:17.253Z","published":"2026-06-23T18:18:03.927Z","url":"https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-49859"},{"published":"2026-06-16T19:02:55Z","url":"https://api.github.com/advisories/GHSA-cpgj-f7g3-2pp2","html_url":"https://github.com/advisories/GHSA-cpgj-f7g3-2pp2","id":"GHSA-cpgj-f7g3-2pp2","imported":"2026-08-05T06:30:41.504Z","modified":"2026-07-20T21:01:14Z"},{"modified":"2026-06-24T14:23:09Z","published":"2026-06-23T17:14:16Z","url":"https://euvdservices.enisa.europa.eu/api/enisaid?id=EUVD-2026-38541","html_url":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-38541","id":"EUVD-2026-38541","imported":"2026-08-05T06:30:31.318Z"}]},"references":[{"type":"WEB","url":"https://github.com/advisories/GHSA-cpgj-f7g3-2pp2"},{"type":"WEB","url":"https://github.com/denoland/deno/security/advisories/GHSA-cpgj-f7g3-2pp2"},{"type":"WEB","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-49859"}],"affected":[{"package":{"name":"Deno_jll","ecosystem":"Julia","purl":"pkg:julia/Deno_jll?uuid=04572ae6-984a-583e-9378-9577a1c2574d"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.8.1+0"}]}],"database_specific":{"source":"https://github.com/JuliaLang/SecurityAdvisories.jl/tree/generated/osv/2026/JLSEC-2026-1164.json"}}],"schema_version":"1.8.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N"}],"credits":[{"name":"7thParkk","contact":["https://github.com/7thParkk"],"type":"REPORTER"},{"name":"alcls01111","contact":["https://github.com/alcls01111"],"type":"REPORTER"}]}