Vulnerability-Lookup

GHSA-5JGF-P345-68V8

Vulnerability from github – Published: 2026-09-02 15:44 – Updated: 2026-09-02 15:44

Summary

fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references

Details

Impact

fast-uri canonicalizes a host to its ASCII form only when the input carries an explicit scheme. When resolve() resolves a scheme-relative reference (//host/) against a scheme-bearing base, it still emits the host verbatim even though the effective scheme is known, so re-parsing the resolved URI yields a different host than the one resolve() returned. An application that resolves an untrusted reference with fast-uri and then checks or routes on the resulting host can make a policy decision on one host and reach another. This is an incomplete-fix variant of CVE-2026-13676, whose IDN canonicalization was applied only to the scheme-bearing form.

Patches

Upgrade to fast-uri 2.4.5, 3.1.6, or 4.1.3. resolve() now canonicalizes the host once the effective scheme is known, and fails closed if a raw non-ASCII host cannot be converted.

Workarounds

Resolve scheme-relative references against a base that carries a scheme before performing any host-policy or origin check.

Severity

7.5 (High)


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

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "fast-uri"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.4.2"
            },
            {
              "fixed": "2.4.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "fast-uri"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.1.3"
            },
            {
              "fixed": "3.1.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "fast-uri"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.0.1"
            },
            {
              "fixed": "4.1.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-75931"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-436"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-02T15:44:30Z",
    "nvd_published_at": "2026-08-24T10:16:40Z",
    "severity": "HIGH"
  },
  "details": "### Impact\n\n`fast-uri` canonicalizes a host to its ASCII form only when the input carries an explicit scheme. When `resolve()` resolves a scheme-relative reference (`//host/`) against a scheme-bearing base, it still emits the host verbatim even though the effective scheme is known, so re-parsing the resolved URI yields a different host than the one `resolve()` returned. An application that resolves an untrusted reference with `fast-uri` and then checks or routes on the resulting host can make a policy decision on one host and reach another. This is an incomplete-fix variant of CVE-2026-13676, whose IDN canonicalization was applied only to the scheme-bearing form.\n\n### Patches\n\nUpgrade to `fast-uri` 2.4.5, 3.1.6, or 4.1.3. `resolve()` now canonicalizes the host once the effective scheme is known, and fails closed if a raw non-ASCII host cannot be converted.\n\n### Workarounds\n\nResolve scheme-relative references against a base that carries a scheme before performing any host-policy or origin check.",
  "id": "GHSA-5jgf-p345-68v8",
  "modified": "2026-09-02T15:44:30Z",
  "published": "2026-09-02T15:44:30Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fast-uri/security/advisories/GHSA-5jgf-p345-68v8"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-75931"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fast-uri/commit/0256bc8d1f28b5d0ac657faf67e2411a189dfcb5"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fast-uri/commit/444ecdad447db2cc23c4d422acc6f0daa6fa8eef"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fast-uri/commit/4e4ebd8b245f6ca16e448203559eea3e545453a3"
    },
    {
      "type": "WEB",
      "url": "https://cna.openjsf.org/security-advisories.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/fastify/fast-uri"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fast-uri/releases/tag/v2.4.5"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fast-uri/releases/tag/v3.1.6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fast-uri/releases/tag/v4.1.3"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references"
}

CVE-2026-75931 (GCVE-0-2026-75931)

Vulnerability from cvelistv5 – Published: 2026-08-24 09:30 – Updated: 2026-08-24 16:28

Title

fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references

Summary

fast-uri is a URI parser for Node.js. It canonicalizes a host to its ASCII form only when the input carries an explicit scheme, so a scheme-relative reference such as a host preceded by two slashes is returned with its host verbatim and no error set. As a result fast-uri's own entry points disagree with each other: parse, resolve, normalize, and equal can yield different hosts for the same input depending only on whether a scheme is written out, and equal can return opposite verdicts for the same pair of hosts. An application that extracts a host with fast-uri to check it against a policy list and then resolves the same reference can make its decision on one host while the destination is another, enabling host confusion and policy bypass. The affected versions are 2.4.2 up to but not including 2.4.5, 3.1.3 up to but not including 3.1.6, and 4.0.1 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which canonicalize the host consistently across the resolve path. Users should upgrade to a patched version.

Severity

7.5 (High)


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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-08-24 16:28 UTC

CWE

CWE-436 - Interpretation Conflict

Assigner

openjs redhat root

References

2 references

URL	Tags
https://github.com/fastify/fast-uri/security/advi…
https://cna.openjsf.org/security-advisories.html

Impacted products

1 product

Vendor	Product	Version
fast-uri	fast-uri	Affected: 2.4.2 , < 2.4.5 (semver) Unaffected: 2.4.5 (semver) Affected: 3.1.3 , < 3.1.6 (semver) Unaffected: 3.1.6 (semver) Affected: 4.0.1 , < 4.1.3 (semver) Unaffected: 4.1.3 (semver)

Credits

baeseungwon1010 mcollina UlisesGascon

Show details on NVD website

JSON

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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.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.