# CVE-2026-84292: fast-uri authority injection via unvalidated port in serialize

Source: https://junglewise.ai/threats/cve-2026-84292-fast-uri-authority-injection-via-unvalidated-port-in-serialize  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-02. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-84292 · Severity: high · CVSS 7.5 · Published 2026-09-02

fast-uri is a JavaScript library for parsing, normalizing, and serializing URIs. An attacker can inject malicious authority components (hostname redirects) by passing an unvalidated port value containing special characters to the serialize, normalize, or equal functions. This allows an attacker to redirect traffic intended for a legitimate host to an attacker-controlled server without the application detecting the change.

Technologies: [fast-uri (npm)](https://junglewise.ai/threats/technologies/npm-fast-uri). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-84292 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-84292 being exploited in the wild.

**How severe is CVE-2026-84292?** High severity, with a CVSS score of 7.5, published 2 September 2026.

**Which products and versions are affected?** fast-uri (npm) SEMVER:introduced=0,fixed=2.4.6.

**Is there a fix for CVE-2026-84292?** Yes. fast-uri (npm): upgrade to 2.4.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-84292 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-84292?** Check whether you run fast-uri (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- fast-uri (npm): upgrade to 2.4.6 or later

  ```sh
  npm install fast-uri@2.4.6
  ```


## Technical details

The vulnerability is an improper encoding/escaping issue (CWE-116) in fast-uri's recomposeAuthority function. When serializing a URI, the library properly escapes userinfo and host components but concatenates the port value verbatim without validating that it contains only digits per RFC 3986. An attacker can inject authority delimiters (such as @) in the port parameter, which reorders the URI structure—demoting the intended host to the userinfo section and inserting an attacker-controlled host as the actual authority. The attack is network-reachable with no authentication or user interaction required and affects applications that construct URIs from untrusted port values via serialize(), normalize(), or equal() methods. Patches are available in fast-uri 2.4.6, 3.1.7, and 4.1.4, which now validate that the port is a digit sequence.

## Affected products

- OpenJS Foundation fast-uri before 2.4.6, 3.0.0 before 3.1.7, 4.0.0 before 4.1.4

## Identifiers

- CVE-2026-84292
- GHSA-qw65-cvwx-89v3

## Timeline

- 2026-09-02: disclosed: CVE-2026-84292 published
- 2026-09-02: patched: Patches released in versions 2.4.6, 3.1.7, and 4.1.4

## References

- [https://cna.openjsf.org/security-advisories.html](https://cna.openjsf.org/security-advisories.html)
- [https://github.com/fastify/fast-uri/security/advisories/GHSA-qw65-cvwx-89v3](https://github.com/fastify/fast-uri/security/advisories/GHSA-qw65-cvwx-89v3)

## Related threats

- [fast-uri vulnerable to scheme injection via an unescaped first-segment colon in suffix references](https://junglewise.ai/threats/cve-2026-110725-fast-uri-is-a-dependency-free-rfc-3986-uri-parser-and-serializer)
- [fast-uri URI scheme spoofing via percent-encoded scheme](https://junglewise.ai/threats/cve-2026-110306-fast-uri-is-a-dependency-free-rfc-3986-uri-parser-and-serializer)
- [fast-uri host confusion via unchecked WHATWG canonicalization](https://junglewise.ai/threats/cve-2026-110180-fast-uri-is-a-dependency-free-rfc-3986-uri-parser-and-serializer)
- [fast-uri vulnerable to improper path equivalence in relative reference normalization](https://junglewise.ai/threats/cve-2026-110095-fast-uri-is-a-dependency-free-rfc-3986-uri-parser-and-serializer)
- [fast-uri mailto header injection via percent-encoded field-name desynchronization](https://junglewise.ai/threats/cve-2026-86818-fast-uri-mailto-header-injection-via-percent-encoded-field-name)