Vulnerability-Lookup

GHSA-JQFF-G426-HQXP

Vulnerability from github – Published: 2026-09-02 15:41 – Updated: 2026-09-02 15:41

Summary

fast-uri vulnerable to host confusion via percent-encoded scheme normalization

Details

Impact

fast-uri decodes percent-encoded characters in the scheme component with the legacy global unescape() and serializes the result back as raw characters, without re-escaping it or validating it as a scheme. A scheme that decodes to characters outside the RFC 3986 scheme grammar can therefore introduce structure the original input did not contain.

For example, %2f%2fevil.example:/pwn parses with no authority (parse().host is undefined), but resolve() and normalize() return //evil.example:/pwn, which reparses with host evil.example. The %uXXXX form (%u002f%u002fevil.example:/pwn) produces the same result, and a scheme containing %0d%0a reaches the output as a raw CR LF.

Applications that normalize or resolve untrusted URLs before a redirect check, host allowlist, or outbound request decision, especially ones that treat a missing authority as same-origin, can be steered to an attacker-chosen authority, and a normalized URI placed in a response header can carry an injected CR LF.

Patches

Upgrade to fast-uri >= 4.1.3, or >= 3.1.6 in the v3.x release line, or >= 2.4.5 in the v2.x release line.

Workarounds

None. Upgrade to the 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

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "fast-uri"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.3.1"
            },
            {
              "fixed": "2.4.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "fast-uri"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "3.1.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "fast-uri"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.0.0"
            },
            {
              "fixed": "4.1.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-76172"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-177"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-02T15:41:53Z",
    "nvd_published_at": "2026-08-24T11:16:40Z",
    "severity": "HIGH"
  },
  "details": "### Impact\n\n`fast-uri` decodes percent-encoded characters in the scheme component with the legacy global `unescape()` and serializes the result back as raw characters, without re-escaping it or validating it as a scheme. A scheme that decodes to characters outside the RFC 3986 scheme grammar can therefore introduce structure the original input did not contain.\n\nFor example, `%2f%2fevil.example:/pwn` parses with no authority (`parse().host` is `undefined`), but `resolve()` and `normalize()` return `//evil.example:/pwn`, which reparses with host `evil.example`. The `%uXXXX` form (`%u002f%u002fevil.example:/pwn`) produces the same result, and a scheme containing `%0d%0a` reaches the output as a raw CR LF.\n\nApplications that normalize or resolve untrusted URLs before a redirect check, host allowlist, or outbound request decision, especially ones that treat a missing authority as same-origin, can be steered to an attacker-chosen authority, and a normalized URI placed in a response header can carry an injected CR LF.\n\n### Patches\n\nUpgrade to `fast-uri` \u003e= 4.1.3, or \u003e= 3.1.6 in the v3.x release line, or \u003e= 2.4.5 in the v2.x release line.\n\n### Workarounds\n\nNone. Upgrade to the patched version.",
  "id": "GHSA-jqff-g426-hqxp",
  "modified": "2026-09-02T15:41:53Z",
  "published": "2026-09-02T15:41:53Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fast-uri/security/advisories/GHSA-jqff-g426-hqxp"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-76172"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fast-uri/commit/37f3417c82994279656854f83ce938acd81c3862"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fast-uri/commit/a941e626411f576f8d90883231e57b6c9d0ff98b"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fastify/fast-uri/commit/c6a74bfd9d8c6b0df5362b3c7ae88d8021cb1e39"
    },
    {
      "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 percent-encoded scheme normalization"
}

CVE-2026-76172 (GCVE-0-2026-76172)

Vulnerability from cvelistv5 – Published: 2026-08-24 10:07 – Updated: 2026-08-24 14:29

Title

fast-uri vulnerable to host confusion via percent-encoded scheme normalization

Summary

fast-uri is a URI parser for Node.js. During parsing it runs a legacy decoding pass over the scheme component and never re-escapes the result, and serialization writes the scheme back out verbatim, unlike the host component which is re-escaped. As a result an input whose scheme carries percent-encoded slashes parses as a scheme with no authority, so the parsed host and error are both undefined, yet resolving or normalizing that same input emits a network-path reference whose authority is attacker-chosen and re-parses to that host. An application that allowlists on the parsed host, or treats a reference with no authority as safe to resolve against its base, gets the opposite of what it checked, giving an off-site redirect, server-side request forgery, or address-policy bypass. The legacy decoder also expands non-standard escape forms, widening the issue past upstream filters, and control characters in the scheme can reach the output as raw carriage return and line feed. The affected versions are 2.3.1 up to but not including 2.4.5, 3.0.0 up to but not including 3.1.6, and 4.0.0 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which reject a scheme that is not valid after decoding. 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 14:29 UTC

CWE

CWE-177 - Improper Handling of URL Encoding (Hex Encoding)

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: 2.3.1 , < 2.4.5 (semver) Unaffected: 2.4.5 (semver) Affected: 3.0.0 , < 3.1.6 (semver) Unaffected: 3.1.6 (semver) Affected: 4.0.0 , < 4.1.3 (semver) Unaffected: 4.1.3 (semver)

Credits

YashvantHange 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.