{"id":"CVE-2026-49860","aliases":["GHSA-83pc-3rw9-qpwj"],"url":"https://o3.security/vulnerability/CVE-2026-49860","summary":"Deno: WebSocket API sandbox bypass via missing post-DNS check","details":"## Summary\n\nWhen a WebSocket connection was opened, Deno checked the destination hostname\nagainst `--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 connect to hosts that the user intended\nto block. In practice this means network isolation rules — for example,\nblocking access to `localhost` or internal services — could be silently\ncircumvented by a malicious or compromised dependency.\n\n`Deno.connect` and `fetch()` were not affected by this specific issue (a\ncompanion advisory covers `fetch()`).\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.","published":"2026-06-23T17:15:05.749Z","modified":"2026-10-28T02:30:22.014454758Z","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":0.03722,"asOf":"2026-09-01"},"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-2026-49860.json"},{"type":"ADVISORY","url":"https://github.com/denoland/deno/security/advisories/GHSA-83pc-3rw9-qpwj"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-49860"},{"type":"PACKAGE","url":"https://github.com/denoland/deno"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:22.014454758Z"}}