fast-uri vulnerable to mailto header injection via percent-encoded field-name desynchronization

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-86818
StatePUBLISHED
Assigneropenjs
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-15 11:17:12 UTC
Updated2026-09-15 13:16:44 UTC
Descriptionfast-uri is a dependency-free RFC 3986 URI parser for Node.js, used by Fastify and ajv, that added a mailto scheme parser in version 4.1.3. In versions 4.1.3 and 4.1.4, the mailto parser compares each query field name to the reserved names to, subject, and body while the name is still percent-encoded, and decodes it only when storing it as a generic header, so a percent-encoded spelling of a reserved field name is not recognized as that field at parse time but is re-emitted as the literal field name when the parsed URI is serialized. An application that validates, logs, or displays the recipient list from the first parse and then serializes the URI and sends it can silently gain an attacker-chosen recipient, and the subject and body fields can be smuggled across the same roundtrip. The issue is fixed in fast-uri 4.1.5, and users should upgrade to 4.1.5 or later. As a workaround, do not act on a mailto URI that fast-uri has re-serialized without first decoding and re-validating its recipient, subject, and body fields.

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-172 | CWE-436 | CWE-172 CWE-172: Encoding Error | CWE-436 CWE-436: Interpretation Conflict

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 4.1.3 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-jvvf-x445-j334 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: manus-use (en)

CNA: mcollina (en)

CNA: UlisesGascon (en)

CNA: manus-pi (en)

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