# CVE-2026-18446: fast-uri vulnerable to host confusion via backslash authority introducer

> CVE-2026-18446: fast-uri vulnerable to host confusion via backslash authority introducer. CVSS 7.5 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-18446
Last updated: 2026-09-02T14:42:38Z

- Published: 2026-07-31 14:37 UTC · Updated: 2026-09-02 14:42 UTC · Assigner: openjs
- CVSS: 7.5 (CVSS 3.1) · Severity: High · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- EPSS: 0.38%, 32th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-436

## Description

fast-uri before 4.1.2, 3.1.5, and 2.4.4 requires a literal double forward slash to recognize a URI authority, so a reference that uses a backslash based introducer in place of it (backslash backslash, forward slash backslash, or backslash forward slash) is parsed with no authority and folds into the path. Node's native WHATWG URL parser instead treats a backslash as interchangeable with a forward slash for special schemes, so the two parsers extract different hosts from the same input. Applications that use fast-uri to enforce host based policy such as allowlists, SSRF filtering, or redirect validation before passing the same URL into Node's URL or fetch consumers can be steered to an unintended host. Upgrade to fast-uri 4.1.2, 3.1.5, or 2.4.4.

## Affected vendors and products

- fast-uri: fast-uri

## Tracked companies

- [Bitbucket](https://rewindex.com/company/bitbucket.md)
- [Jira](https://rewindex.com/company/jira.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-18446)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-18446)
- [https://cna.openjsf.org/security-advisories.html](https://cna.openjsf.org/security-advisories.html)
- [https://github.com/fastify/fast-uri/security/advisories/GHSA-7p8r-x3mc-p8w7](https://github.com/fastify/fast-uri/security/advisories/GHSA-7p8r-x3mc-p8w7)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-18446 · Markdown: https://rewindex.com/cve/CVE-2026-18446.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-18446 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:10:47.193Z