CVE-2026-13676: Fast uri Fast-uri Vulnerable To Host Confusion Vulnerability

HIGH
Advisory Identifier: GHSA-4c8g-83qw-93j6
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CVSS 7.5
CWE-436 CWE-551
Published
Advisory Summary

CVE-2026-13676 is a HIGH (CVSS 7.5) fast-uri vulnerable to host confusion vulnerability (CWE-436: Interpretation Conflict) affecting Fast uri libraries in the npm ecosystem. The issue involves fast-uri vulnerable to host confusion via failed idn canonicalization. Remediation is available by upgrading affected packages to version 4.0.1, 3.1.3, 2.4.2.

CVE-2026-13676 at a Glance

CVE Identifier CVE-2026-13676
GHSA Identifier GHSA-4c8g-83qw-93j6
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-436: Interpretation Conflict
Affected Product Fast uri
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity High (I:H)
Availability None (A:N)

How to Fix CVE-2026-13676

To remediate this vulnerability, upgrade all affected Fast uri dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

fast-uri fixed: 4.0.1 
npm install fast-uri@4.0.1
fast-uri fixed: 3.1.3 
npm install fast-uri@3.1.3
fast-uri fixed: 2.4.2 
npm install fast-uri@2.4.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls fast-uri

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-13676, inspect your project dependencies using npm:

npm ls fast-uri

Analyze the terminal output to locate any version of Fast uri in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.0.1), your application is affected.

Note: The npm ls fast-uri command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-436: Interpretation Conflict, where product a handles inputs or steps differently than product b, which causes a to perform incorrect actions based on its perception of b's state. In Fast uri, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact `fast-uri` versions `>= 2.3.1, <= 4.0.0` fail to canonicalize Unicode/IDN hostnames for HTTP-family URLs. The IDN conversion path calls `URL.domainToASCII(...)` on the global WHATWG `URL` constructor, where that helper does not exist. The resulting `TypeError` is silently routed into `parsed.error`, but `parse()`, `normalize()`, and `equal()` all return with the host left in its original Unicode form. For example, `http://127。0。0。1/` is treated by `fast-uri` as host `127。0。0。1`, while Node's WHATWG URL parser and `fetch()` canonicalize the same input to `127.0.0.1`. Applications that use `fast-uri` to enforce host-based policy (denylists, loopback filtering, redirect validation, outbound proxy routing) before passing the same URL into Node's URL or `fetch()` consumers see a policy/use desync and can be steered to an unintended destination. ### Patches Upgrade to `fast-uri` v4.0.1, v3.1.3, or v2.4.2 ### Workarounds None. Upgrade to the patched version.

CVE-2026-13676 Affected Fast uri Versions

3 component(s)
Fixed Versions:
4.0.13.1.32.4.2
Product / Package Ecosystem Affected Versions Fixed Version
fast-uri
npm/fast-uri
npm
≥ 4.0.0
< 4.0.1
4.0.1
fast-uri
npm/fast-uri
npm
≥ 3.0.0
< 3.1.3
3.1.3
fast-uri
npm/fast-uri
npm
≥ 2.3.1
< 2.4.2
2.4.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/fastify/fast-uri/security/advisories/GHSA-4c8g-83qw-93j6
NVD — CVE-2026-13676 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-13676
Fast uri Source Repository REPOSITORY
https://github.com/fastify/fast-uri/pull/188
Security Fix Commit FIX COMMIT
https://github.com/fastify/fast-uri/commit/2a6d357a18a68e6d812824379fd3388a1ae50d05
Security Fix Commit FIX COMMIT
https://github.com/fastify/fast-uri/commit/21ea1f9d70495c931f55dff893a8fa38f4f2e6bd
Security Fix Commit FIX COMMIT
https://github.com/fastify/fast-uri/commit/01db48010f594b98f7b323be18b393791c66ed1d
access.redhat.com/errata/rhsa-2026:63... WEB
https://access.redhat.com/errata/RHSA-2026:63371
access.redhat.com/errata/rhsa-2026:61... WEB
https://access.redhat.com/errata/RHSA-2026:61314
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https://access.redhat.com/errata/RHSA-2026:60520
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https://access.redhat.com/errata/RHSA-2026:60386
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https://access.redhat.com/errata/RHSA-2026:59593
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https://access.redhat.com/errata/RHSA-2026:57590
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https://access.redhat.com/errata/RHSA-2026:57194
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https://access.redhat.com/errata/RHSA-2026:57191
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https://access.redhat.com/errata/RHSA-2026:57013
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https://access.redhat.com/errata/RHSA-2026:56431
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https://access.redhat.com/errata/RHSA-2026:56366
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https://access.redhat.com/errata/RHSA-2026:66488
access.redhat.com/errata/rhsa-2026:66... WEB
https://access.redhat.com/errata/RHSA-2026:66545
Fast uri Security Information SECURITY
https://access.redhat.com/security/cve/CVE-2026-13676
bugzilla.redhat.com/show_bug.cgi WEB
https://bugzilla.redhat.com/show_bug.cgi?id=2494197
Fast uri Security Information SECURITY
https://cna.openjsf.org/security-advisories.html
Fast uri Source Repository REPOSITORY
https://github.com/fastify/fast-uri
Fast uri Release RELEASE
https://github.com/fastify/fast-uri/releases/tag/v2.4.2
Fast uri Release RELEASE
https://github.com/fastify/fast-uri/releases/tag/v3.1.3
Fast uri Release RELEASE
https://github.com/fastify/fast-uri/releases/tag/v4.0.1
Fast uri Security Information SECURITY
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-13676.json
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https://access.redhat.com/errata/RHSA-2026:37186
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https://access.redhat.com/errata/RHSA-2026:37585
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https://access.redhat.com/errata/RHSA-2026:37628
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https://access.redhat.com/errata/RHSA-2026:40118
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https://access.redhat.com/errata/RHSA-2026:40262
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https://access.redhat.com/errata/RHSA-2026:40765
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https://access.redhat.com/errata/RHSA-2026:40945
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https://access.redhat.com/errata/RHSA-2026:41066
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https://access.redhat.com/errata/RHSA-2026:41929
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https://access.redhat.com/errata/RHSA-2026:43038
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https://access.redhat.com/errata/RHSA-2026:44239
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https://access.redhat.com/errata/RHSA-2026:44268
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https://access.redhat.com/errata/RHSA-2026:47728
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https://access.redhat.com/errata/RHSA-2026:48124
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https://access.redhat.com/errata/RHSA-2026:48126
access.redhat.com/errata/rhsa-2026:49... WEB
https://access.redhat.com/errata/RHSA-2026:49642
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https://access.redhat.com/errata/RHSA-2026:50340
access.redhat.com/errata/rhsa-2026:50... WEB
https://access.redhat.com/errata/RHSA-2026:50479
access.redhat.com/errata/rhsa-2026:50... WEB
https://access.redhat.com/errata/RHSA-2026:50758
access.redhat.com/errata/rhsa-2026:51... WEB
https://access.redhat.com/errata/RHSA-2026:51196
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https://access.redhat.com/errata/RHSA-2026:51197
access.redhat.com/errata/rhsa-2026:51... WEB
https://access.redhat.com/errata/RHSA-2026:51342
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https://access.redhat.com/errata/RHSA-2026:51348
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https://access.redhat.com/errata/RHSA-2026:51349
access.redhat.com/errata/rhsa-2026:54... WEB
https://access.redhat.com/errata/RHSA-2026:54760

Frequently Asked Questions

What is CVE-2026-13676?
CVE-2026-13676 is a security vulnerability in Fast uri involving fast-uri vulnerable to host confusion via failed IDN canonicalization under CWE-436: Interpretation Conflict.
Which Fast uri versions are affected?
Affected versions include releases prior to 4.0.1, 3.1.3, 2.4.2 across affected packages: fast-uri.
What version fixes CVE-2026-13676?
Upgrading to 4.0.1, 3.1.3, 2.4.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is fast-uri affected?
Yes, fast-uri is affected in releases prior to 4.0.1, 3.1.3, 2.4.2. Upgrade your dependency to 4.0.1, 3.1.3, 2.4.2 or later.
What is the CVSS score of CVE-2026-13676?
CVE-2026-13676 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.
What CWE is associated with CVE-2026-13676?
CVE-2026-13676 is classified under CWE-436: Interpretation Conflict (Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.).
How can I check npm dependencies for CVE-2026-13676?
Run the dependency tree command: 'npm ls fast-uri'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
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  "id" : "GHSA-4c8g-83qw-93j6",
  "modified" : "2026-09-11T15:32:25Z",
  "published" : "2026-07-21T19:03:11Z",
  "aliases" : [ "CVE-2026-13676" ],
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  "details" : "### Impact\n\n`fast-uri` versions `>= 2.3.1, <= 4.0.0` fail to canonicalize Unicode/IDN hostnames for HTTP-family URLs. The IDN conversion path calls `URL.domainToASCII(...)` on the global WHATWG `URL` constructor, where that helper does not exist. The resulting `TypeError` is silently routed into `parsed.error`, but `parse()`, `normalize()`, and `equal()` all return with the host left in its original Unicode form.\n\nFor example, `http://127。0。0。1/` is treated by `fast-uri` as host `127。0。0。1`, while Node's WHATWG URL parser and `fetch()` canonicalize the same input to `127.0.0.1`.\n\nApplications that use `fast-uri` to enforce host-based policy (denylists, loopback filtering, redirect validation, outbound proxy routing) before passing the same URL into Node's URL or `fetch()` consumers see a policy/use desync and can be steered to an unintended destination.\n\n### Patches\n\nUpgrade to `fast-uri` v4.0.1, v3.1.3, or v2.4.2\n\n### Workarounds\n\nNone. Upgrade to the patched version.",
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}