fast-uri vulnerable to inconsistent host case normalization via percent-encoded octets

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-86472
StatePUBLISHED
Assigneropenjs
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-15 11:17:12 UTC
Updated2026-09-15 13:16:43 UTC
Descriptionfast-uri is a dependency-free RFC 3986 URI parser for Node.js, used by Fastify and ajv. In versions before 2.4.7, from 3.0.0 through 3.1.7, and from 4.0.0 through 4.1.4, fast-uri folds the host to lowercase before it percent-decodes the host, so a percent-encoded uppercase octet such as %41 decodes to a literal A that is never folded. For a scheme-relative reference such as //host there is no scheme, so the host canonicalization that would normally repair this does not run, and parse, normalize, and equal then disagree on the same host. An application that makes a case-sensitive host decision on fast-uri output, for example a host allowlist or denylist that compares the parsed host or uses equal, can be steered past the check with a percent-encoded uppercase octet, and because hostnames are case-insensitive in DNS and HTTP the evading spelling still reaches the host the check meant to gate. The issue is fixed in fast-uri 2.4.7, 3.1.8, and 4.1.5, and users should upgrade to one of those versions or later. As a workaround, compare hosts case-insensitively by lowercasing the parsed host before any allowlist or denylist decision.

Risk And Classification

Primary CVSS: v3.1 4.8 MEDIUM from ce714d77-add3-4f53-aff5-83d477b104bb

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

Problem Types: CWE-178 | CWE-178 CWE-178: Improper Handling of Case Sensitivity

VersionSourceTypeScoreSeverityVector
3.1ce714d77-add3-4f53-aff5-83d477b104bbSecondary4.8MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
3.1CNACVSS4.8MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS v3.1 Breakdown

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

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Fast-uri Fast-uri affected 2.4.7 semver Not specified
CNA Fast-uri Fast-uri unaffected 2.4.7 semver Not specified
CNA Fast-uri Fast-uri affected 3.0.0 3.1.8 semver Not specified
CNA Fast-uri Fast-uri unaffected 3.1.8 semver Not specified
CNA Fast-uri Fast-uri affected 4.0.0 4.1.5 semver Not specified
CNA Fast-uri Fast-uri unaffected 4.1.5 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-hrr3-gc8f-f4qj 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: fg0x0 (en)

CNA: mcollina (en)

CNA: UlisesGascon (en)

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