{"id":"EUVD-2026-78403","revision":null,"records":[{"revision":"720761dc798247988475730566eaa96a","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-86818","aliases":[],"title":"fast-uri vulnerable to mailto header injection via percent-encoded field-name desynchronization","description":"fast-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.","state":0,"publishedAt":"2026-09-15T10:40:38.461+00:00","modifiedAt":"2026-09-15T12:31:55.631+00:00","affected":[{"ecosystem":"Vendor product","name":"fast-uri","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"fast-uri\",\n                    \"product\": \"fast-uri\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"versions\": [\n                        {\n                            \"versionType\": \"semver\",\n                            \"status\": \"affected\",\n                            \"version\": \"4.1.3\",\n                            \"lessThan\": \"4.1.5\"\n                        },\n                        {\n                            \"versionType\": \"semver\",\n                            \"status\": \"unaffected\",\n                            \"version\": \"4.1.5\"\n                        }\n                    ],\n                    \"packageURL\": \"pkg:npm/fast-uri\"\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N","score":4.8,"severity":"MEDIUM"}],"references":["https://github.com/fastify/fast-uri/security/advisories/GHSA-jvvf-x445-j334","https://cna.openjsf.org/security-advisories.html"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-86818","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-86818","identifiers":["CVE-2026-86818"]},"retained":false,"historicalAffected":[]},{"revision":"7e3059cbf08942ed9166e8e39cb700c2","observedAt":"2026-11-11T17:02:44.279+00:00","statement":{"source":"euvd","id":"EUVD-2026-78403","aliases":["CVE-2026-86818","GHSA-jvvf-x445-j334"],"title":"fast-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 …","description":"fast-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.","state":0,"publishedAt":null,"modifiedAt":null,"affected":[],"metrics":[{"system":"EUVD CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N","score":4.8,"severity":null}],"references":["https://github.com/fastify/fast-uri/security/advisories/GHSA-jvvf-x445-j334","https://cna.openjsf.org/security-advisories.html"],"sourceUrl":"https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-78403","license":"ENISA EUVD · source terms and attribution apply","enrichment":{"sourceStatus":null,"weaknesses":[],"productCriteria":[],"sourceDates":{"datePublished":"Sep 15, 2026, 10:40:38 AM","dateUpdated":"Sep 15, 2026, 12:31:55 PM"},"relatedAdvisories":[],"note":"EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON."},"key":"euvd:EUVD-2026-78403","identifiers":["EUVD-2026-78403","CVE-2026-86818","GHSA-jvvf-x445-j334"]},"retained":false,"historicalAffected":[]},{"revision":"8d41aa4728b4494facacb9be49bc802e","observedAt":"2026-10-25T16:19:16.24+00:00","statement":{"source":"nvd","id":"CVE-2026-86818","aliases":[],"title":"fast-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 …","description":"fast-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.","state":0,"publishedAt":"2026-09-15T11:17:12.453+00:00","modifiedAt":"2026-09-16T19:40:00.317+00:00","affected":[],"metrics":[{"system":"CVSS 3.1 · ce714d77-add3-4f53-aff5-83d477b104bb · Secondary","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N","score":4.8,"severity":"MEDIUM"}],"references":["https://cna.openjsf.org/security-advisories.html","https://github.com/fastify/fast-uri/security/advisories/GHSA-jvvf-x445-j334"],"sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-86818","license":"NIST NVD usage terms; underlying source attribution retained","enrichment":{"sourceStatus":"Awaiting Analysis","weaknesses":["CWE-172","CWE-436"],"productCriteria":[],"sourceDates":{"published":"2026-09-15T11:17:12.453","lastModified":"2026-09-16T19:40:00.317"},"relatedAdvisories":[],"note":"NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON."},"key":"nvd:CVE-2026-86818","identifiers":["CVE-2026-86818"]},"retained":false,"historicalAffected":[]},{"revision":"4f1d6142ba7f418ba4f9f63f19c3e8fa","observedAt":"2026-10-24T13:17:17.793+00:00","statement":{"source":"osv","id":"GHSA-jvvf-x445-j334","aliases":["CVE-2026-86818"],"title":"fast-uri vulnerable to mailto header injection via percent-encoded field-name desynchronization","description":"### Impact\n\n`fast-uri`'s `mailto` scheme parser compares each query field name to the reserved names (`to`, `subject`, `body`) while the name is still percent-encoded, and only percent-decodes it when storing it as a generic header. On serialize, the decoded name is re-emitted, so a field name such as `%74o` (percent-encoded `to`) is not recognized as a recipient at parse time (`parse().to` shows only the legitimate recipient) but materializes as a literal `to=` field after `serialize()`, and reparsing then treats it as a recipient. The same technique smuggles `subject` and `body` through `%73ubject` and `%62ody`.\n\nAn application that parses an untrusted mailto URI, makes a display, allowlist, or logging decision on `parse().to`, then re-serializes the result and passes the serialized string to a mail client or an outbound send path can gain an attacker-chosen recipient, subject, or body that was not visible when the recipient list was checked. A scanner inspecting the raw input for an extra `to=` sees nothing, because the injected field appears only after `fast-uri` serializes.\n\n### Patches\n\nUpgrade to `fast-uri` 4.1.5.\n\n### Workarounds\n\nPercent-decode and compare mailto field names case-insensitively before trusting `parse().to`, or re-check the recipient list on the serialized output rather than only on the initial parse, until upgrading.","state":0,"publishedAt":"2026-09-29T23:51:16+00:00","modifiedAt":"2026-09-30T00:00:03.8545188+00:00","affected":[{"ecosystem":"npm","name":"fast-uri","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"4.1.3"},{"kind":"fixed","version":"4.1.5"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"MODERATE"}],"references":["https://github.com/fastify/fast-uri/security/advisories/GHSA-jvvf-x445-j334","https://nvd.nist.gov/vuln/detail/CVE-2026-86818","https://github.com/fastify/fast-uri/commit/f40a88f33e684a46faec3f5b820bcbb1e85add64","https://cna.openjsf.org/security-advisories.html","https://github.com/fastify/fast-uri","https://github.com/fastify/fast-uri/releases/tag/v4.1.5"],"sourceUrl":"https://github.com/advisories/GHSA-jvvf-x445-j334","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-jvvf-x445-j334","identifiers":["GHSA-jvvf-x445-j334","CVE-2026-86818"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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