GHSA-83PC-3RW9-QPWJ
Vulnerability from github – Published: 2026-06-16 19:04 – Updated: 2026-06-16 19:04Summary
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.
Impact
Code running under --deny-net could connect to hosts that the user intended
to block. In practice this means network isolation rules — for example,
blocking access to localhost or internal services — could be silently
circumvented by a malicious or compromised dependency.
Deno.connect and fetch() were not affected by this specific issue (a
companion advisory covers fetch()).
Who is affected
Users who:
- run untrusted or third-party code with
deno run, and - rely on
--deny-netto restrict which hosts that code can reach.
If you do not use --deny-net, or if you only run fully trusted code, you are
not affected.
Workaround
No workaround is available short of upgrading. If upgrading immediately is not
possible, avoid granting --allow-net to untrusted code that also has
--deny-net restrictions you depend on for security.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 2.8.0"
},
"package": {
"ecosystem": "crates.io",
"name": "deno"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2.8.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-49860"
],
"database_specific": {
"cwe_ids": [
"CWE-918"
],
"github_reviewed": true,
"github_reviewed_at": "2026-06-16T19:04:07Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"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 \u2014 for example,\nblocking access to `localhost` or internal services \u2014 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.",
"id": "GHSA-83pc-3rw9-qpwj",
"modified": "2026-06-16T19:04:08Z",
"published": "2026-06-16T19:04:07Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/denoland/deno/security/advisories/GHSA-83pc-3rw9-qpwj"
},
{
"type": "PACKAGE",
"url": "https://github.com/denoland/deno"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N",
"type": "CVSS_V3"
}
],
"summary": "Deno: WebSocket API sandbox bypass via missing post-DNS check"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.