fast-uri vulnerable to host confusion via backslash authority introducer

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-18446
StatePUBLISHED
Assigneropenjs
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-31 15:16:27 UTC
Updated2026-07-31 18:17:13 UTC
Descriptionfast-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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from ce714d77-add3-4f53-aff5-83d477b104bb

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

Problem Types: CWE-436 | CWE-436 CWE-436: Interpretation Conflict

VersionSourceTypeScoreSeverityVector
3.1ce714d77-add3-4f53-aff5-83d477b104bbSecondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
3.1CNACVSS7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Fast-uri Fast-uri affected 4.0.0 4.1.2 semver Not specified
CNA Fast-uri Fast-uri unaffected 4.1.2 semver Not specified
CNA Fast-uri Fast-uri affected 3.0.0 3.1.5 semver Not specified
CNA Fast-uri Fast-uri unaffected 3.1.5 semver Not specified
CNA Fast-uri Fast-uri affected 2.4.4 semver Not specified
CNA Fast-uri Fast-uri unaffected 2.4.4 semver Not specified

References

ReferenceSourceLinkTags
cna.openjsf.org/security-advisories.html ce714d77-add3-4f53-aff5-83d477b104bb cna.openjsf.org
github.com/fastify/fast-uri/security/advisories/GHSA-7p8r-x3mc-p8w7 ce714d77-add3-4f53-aff5-83d477b104bb github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: alanturing881 (en)

CNA: mcollina (en)

CNA: UlisesGascon (en)

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