{"schema":"threatline.record/2","record":{"id":"CVE-2026-86818","aliases":["GHSA-jvvf-x445-j334"],"summary":"fast-uri vulnerable to mailto header injection via percent-encoded field-name desynchronization","details":"### 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.","categories":["Libraries & packages"],"product":"fast-uri","vendor":"fast-uri","ecosystem":"npm","affected_ranges":[{"source":"GitHub Advisory Database","source_url":"https://github.com/advisories/GHSA-jvvf-x445-j334","source_modified_at":"2026-09-29T23:51:17Z","fetched_at":"2026-10-23T18:42:43.628194Z","package":{"ecosystem":"npm","name":"fast-uri"},"range":">= 4.1.3, < 4.1.5"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-86818","source_modified_at":"2026-09-15T12:31:55.631Z","fetched_at":"2026-10-23T18:45:31.882637Z","product":"fast-uri","vendor":"fast-uri","versions":[{"lessThan":"4.1.5","status":"affected","version":"4.1.3","versionType":"semver"},{"status":"unaffected","version":"4.1.5","versionType":"semver"}],"defaultStatus":"unaffected"},{"source":"OSV","source_url":"https://osv.dev/vulnerability/GHSA-jvvf-x445-j334","source_modified_at":"2026-09-30T00:00:03.854518772Z","fetched_at":"2026-10-23T18:48:36.087640Z","package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"4.1.3"},{"fixed":"4.1.5"}]}],"versions":[]}],"fixed_versions":[{"source":"GitHub Advisory Database","source_url":"https://github.com/advisories/GHSA-jvvf-x445-j334","source_modified_at":"2026-09-29T23:51:17Z","fetched_at":"2026-10-23T18:42:43.628194Z","package":{"ecosystem":"npm","name":"fast-uri"},"version":"4.1.5"},{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-86818","source_modified_at":"2026-09-15T12:31:55.631Z","fetched_at":"2026-10-23T18:45:31.882637Z","package":{"name":"fast-uri","ecosystem":null},"version":"4.1.5","basis":"first unaffected version stated in the CVE record"},{"source":"OSV","source_url":"https://osv.dev/vulnerability/GHSA-jvvf-x445-j334","source_modified_at":"2026-09-30T00:00:03.854518772Z","fetched_at":"2026-10-23T18:48:36.087640Z","package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"version":"4.1.5"}],"cvss":4.8,"severity":"Medium","kev":{"listed":false},"epss":{"probability":0.00253,"percentile":0.15841,"score_date":"2026-10-23"},"published_at":"2026-09-15T10:40:38.461Z","modified_at":"2026-09-30T00:00:03.854518772Z","provenance":[{"source":"GitHub Advisory Database","url":"https://github.com/advisories/GHSA-jvvf-x445-j334","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-09-29T23:51:17Z"},{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-86818","fetched_at":"2026-10-23T18:45:31.882637Z","source_modified_at":"2026-09-15T12:31:55.631Z"},{"source":"OSV","url":"https://osv.dev/vulnerability/GHSA-jvvf-x445-j334","fetched_at":"2026-10-23T18:48:36.087640Z","source_modified_at":"2026-09-30T00:00:03.854518772Z"},{"source":"EPSS","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-86818","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23"}],"sources":["GitHub Advisory Database","CVE List","OSV","EPSS"],"references":[{"source":"CVE List","url":"https://github.com/fastify/fast-uri/security/advisories/GHSA-jvvf-x445-j334"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-86818","source":"GitHub Advisory Database"},{"url":"https://github.com/fastify/fast-uri/commit/f40a88f33e684a46faec3f5b820bcbb1e85add64","source":"GitHub Advisory Database"},{"source":"CVE List","url":"https://cna.openjsf.org/security-advisories.html"},{"url":"https://github.com/fastify/fast-uri/releases/tag/v4.1.5","source":"GitHub Advisory Database"},{"url":"https://github.com/advisories/GHSA-jvvf-x445-j334","source":"GitHub Advisory Database"}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","ssvc":{"exploitation":"none","automatable":"no","technical_impact":"partial","assessed_at":"2026-09-15T12:31:36.232672Z"},"classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":"ecosystem","confidence":"heuristic","reviewed":false},"change_timestamp":"2026-09-30T00:00:03.854518772Z","content_hash":"c8f3ff1ee87c24c27d5d2c60159b0b6342d24f10d234c4b8afe9415c4abd0ff3"}}