Deno: `fetch()` API sandbox bypass via missing DNS resolution check
Exact source revision recorded 24 Oct 2026 13:19:54 UTC. It does not establish the source's current position. Latest evidence.
osv · GHSA-cpgj-f7g3-2pp2
Published## Summary 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. ## Impact Code running under `--deny-net` could reach 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. A companion advisory covers the same class of issue in the WebSocket API. ## Who is affected Users who: - run untrusted or third-party code with `deno run`, and - rely on `--deny-net` to 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. ## Fix The `fetch()` DNS resolver now performs a post-resolution check on every IP address before passing it to the HTTP connector, consistent with how `Deno.connect` already behaved.
- Source published
- 16 Jun 2026 19:02:55 UTC
- Source modified
- 20 Jul 2026 21:15:27 UTC
- Observed here
- 24 Oct 2026 13:19:54 UTC
- Source terms
- GitHub Advisory Database · CC-BY-4.0
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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.
CVSS_V3 · CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
Publisher rating · MODERATE