Vulnerability-Lookup

CVE-2026-49859 (GCVE-0-2026-49859)

Vulnerability from cvelistv5 – Published: 2026-06-23 17:14 – Updated: 2026-06-23 17:14

Title

Deno: `fetch()` API sandbox bypass via missing DNS resolution check

Summary

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

5.2 (Medium)


                        
                          CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

CWE

CWE-693 - Protection Mechanism Failure
CWE-918 - Server-Side Request Forgery (SSRF)

Assigner

GitHub_M

References

1 reference

URL	Tags
https://github.com/denoland/deno/security/advisor…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version
denoland	deno	Affected: < 2.8.1

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "deno",
          "vendor": "denoland",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 2.8.1"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "NONE",
            "baseScore": 5.2,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "LOW",
            "integrityImpact": "LOW",
            "privilegesRequired": "LOW",
            "scope": "CHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-693",
              "description": "CWE-693: Protection Mechanism Failure",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-918",
              "description": "CWE-918: Server-Side Request Forgery (SSRF)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-06-23T17:14:16.888Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/denoland/deno/security/advisories/GHSA-cpgj-f7g3-2pp2",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/denoland/deno/security/advisories/GHSA-cpgj-f7g3-2pp2"
        }
      ],
      "source": {
        "advisory": "GHSA-cpgj-f7g3-2pp2",
        "discovery": "UNKNOWN"
      },
      "title": "Deno: `fetch()` API sandbox bypass via missing DNS resolution check"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-49859",
    "datePublished": "2026-06-23T17:14:16.888Z",
    "dateReserved": "2026-06-01T22:03:19.640Z",
    "dateUpdated": "2026-06-23T17:14:16.888Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-49859",
      "date": "2026-06-14",
      "epss": "0.00021",
      "percentile": "0.06167"
    }
  }
}

GHSA-CPGJ-F7G3-2PP2

Vulnerability from github – Published: 2026-06-16 19:02 – Updated: 2026-06-16 19:02

Summary

Deno: `fetch()` API sandbox bypass via missing DNS resolution check

Details

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.

Severity

5.2 (Medium)


                  
                    CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

Show details on source website

JSON

To clipboard

{
  "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-2026-49859"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-693",
      "CWE-918"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-16T19:02:55Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "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 \u2014 for example, blocking\naccess to `localhost` or internal services \u2014 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.",
  "id": "GHSA-cpgj-f7g3-2pp2",
  "modified": "2026-06-16T19:02:55Z",
  "published": "2026-06-16T19:02:55Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/denoland/deno/security/advisories/GHSA-cpgj-f7g3-2pp2"
    },
    {
      "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: `fetch()` API sandbox bypass via missing DNS resolution 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.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-49859 (GCVE-0-2026-49859)

GHSA-CPGJ-F7G3-2PP2

Summary

Impact

Who is affected

Workaround

Fix

Tags

Sightings

Nomenclature