{"id":"CVE-2026-49859","aliases":["EUVD-2026-38541","GHSA-cpgj-f7g3-2pp2","JLSEC-2026-1164"],"status":"published","title":"Deno: `fetch()` API sandbox bypass via missing DNS resolution check","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.","severity":{"version":"3.1","score":5.2,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.00141,"percentile":0.0348,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-693","CWE-918"],"published":"2026-06-16T19:02:55Z","modified":"2026-10-28T02:30:26Z","fixes":[{"ecosystem":"crates.io","package":"deno","fixed_in":["2.8.1"],"sources":["ghsa","osv"]},{"ecosystem":"Julia","package":"Deno_jll","fixed_in":["2.8.1+0"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"crates.io","package":"deno","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"2.8.0"},{"fixed":"2.8.1"}]}]},{"source":"osv","ecosystem":"crates.io","package":"deno","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.8.1"}]}]},{"source":"osv","ecosystem":"Julia","package":"Deno_jll","ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.8.1+0"}]}]}],"products":[{"vendor":"deno","product":"deno"},{"vendor":"denoland","product":"deno"}],"references":[{"url":"https://github.com/denoland/deno/security/advisories/GHSA-cpgj-f7g3-2pp2","tags":["x_refsource_CONFIRM","Vendor Advisory","advisory","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-49859","tags":["advisory","web"]},{"url":"https://github.com/advisories/GHSA-cpgj-f7g3-2pp2","tags":["web"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/49xxx/CVE-2026-49859.json","tags":["advisory"]},{"url":"https://github.com/denoland/deno","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2026-49859","title":"Deno: `fetch()` API sandbox bypass via missing DNS resolution check","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.","status":"published","published":"2026-06-23T17:14:16.888Z","modified":"2026-06-24T14:23:09.068Z","cvss":[{"version":"3.1","score":5.2,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-693","CWE-918"],"updated_at":"2026-11-02T13:34:59.78118Z"}],"euvd":[{"id":"EUVD-2026-38541","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.","status":"published","published":"2026-06-23T17:14:16Z","modified":"2026-06-24T14:23:09Z","cvss":[{"version":"3.1","score":5.2,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T18:20:30.642628Z"}],"ghsa":[{"id":"GHSA-cpgj-f7g3-2pp2","title":"Deno: `fetch()` API sandbox bypass via missing DNS resolution check","description":"## 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.","status":"published","published":"2026-06-16T19:02:55Z","modified":"2026-07-20T21:01:14Z","cvss":[{"version":"3.1","score":5.2,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-693","CWE-918"],"updated_at":"2026-11-02T14:40:47.245721Z"}],"nvd":[{"id":"CVE-2026-49859","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.","status":"published","published":"2026-06-23T18:18:03.927Z","modified":"2026-10-25T23:10:00.167Z","cvss":[{"version":"3.1","score":5.2,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N","level":"medium","assessor":"secondary"}],"cwes":["CWE-693","CWE-918"],"updated_at":"2026-11-02T14:12:25.288279Z"}],"osv":[{"id":"CVE-2026-49859","title":"Deno: `fetch()` API sandbox bypass via missing DNS resolution check","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.","status":"published","published":"2026-06-23T17:14:16.888Z","modified":"2026-10-28T02:30:26.902548051Z","cvss":[{"version":"3.1","score":5.2,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-693","CWE-918"],"updated_at":"2026-11-02T15:45:07.060148Z"},{"id":"GHSA-cpgj-f7g3-2pp2","title":"Deno: `fetch()` API sandbox bypass via missing DNS resolution check","description":"## 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.","status":"published","published":"2026-06-16T19:02:55Z","modified":"2026-07-20T21:15:27.259698816Z","cvss":[{"version":"3.1","score":5.2,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-693","CWE-918"],"updated_at":"2026-11-02T15:46:45.28161Z"},{"id":"JLSEC-2026-1164","title":"Deno: `fetch()` API sandbox bypass via missing DNS resolution check","description":"## 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.","status":"published","published":"2026-08-05T18:20:40.259Z","modified":"2026-08-05T18:37:02.708842313Z","cvss":[{"version":"3.1","score":5.2,"vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N","level":"medium"}],"updated_at":"2026-11-02T15:47:18.159338Z"}]}}