{"id":"CVE-2026-110306","aliases":["GHSA-w74x-v6f9-j3xg"],"title":"fast-uri vulnerable to URI scheme spoofing via percent-encoded scheme decoding","summary":"fast-uri vulnerable to URI scheme spoofing via percent-encoded scheme decoding","severity":"medium","cvss":6.1,"cwe":["CWE-172","CWE-180","CWE-1286"],"vendor":"fast-uri","product":"fast-uri","ecosystem":"npm","affected":["fast-uri < 2.4.8","fast-uri >= 3.0.0, < 3.1.9","fast-uri >= 4.0.0, < 4.2.3"],"patched":["fast-uri 2.4.8","fast-uri 3.1.9","fast-uri 4.2.3"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T21:41:38Z","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-w74x-v6f9-j3xg","references":[{"url":"https://github.com/fastify/fast-uri/security/advisories/GHSA-w74x-v6f9-j3xg"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-110306"},{"url":"https://github.com/fastify/fast-uri/commit/39933a1f1422986f14e2d844f552238feb40f5d4"},{"url":"https://github.com/fastify/fast-uri/commit/597f254c86d151568511eeb9a1df761fd12520b3"},{"url":"https://github.com/fastify/fast-uri/commit/e60e716f41d1d73717e2d803d20b68d2c6d20a0f"},{"url":"https://cna.openjsf.org/security-advisories.html"},{"url":"https://github.com/fastify/fast-uri/releases/tag/v2.4.8"},{"url":"https://github.com/fastify/fast-uri/releases/tag/v3.1.9"},{"url":"https://github.com/fastify/fast-uri/releases/tag/v4.2.3"},{"url":"https://github.com/advisories/GHSA-w74x-v6f9-j3xg"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-110306.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-110306"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2556005"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-110306"}],"tags":["ghsa","npm","cve.org","csaf","vex","red-hat"],"epss":0.0025,"epssPercentile":0.16213,"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"partial","timestamp":"2026-10-20T19:14:03.847725Z"},"ingestedAt":"2026-10-20T07:55:43.638Z","slug":"CVE-2026-110306","body":"## Overview\n\n### Impact\n\n`fast-uri` percent-decodes the scheme component with the legacy global `unescape()` before validating it, so an input whose decoded scheme is a valid but dangerous token is emitted as a live scheme. RFC 3986 section 3.1 does not allow percent-encoding in a scheme, so no RFC or WHATWG parser treats such input as having that scheme, but `fast-uri` does.\n\nFor example, `normalize('%6Aavascript:alert(1)')` returns `javascript:alert(1)`, `resolve('https://a.example/', '%6Aavascript:alert(1)')` returns `javascript:alert(1)`, and `parse('%6Aavascript:alert(1)').scheme` returns `javascript`. The `%uXXXX` form (`%u006Aavascript:`) produces the same result, and `equal('%68ttp://a/', 'http://a/')` returns `true`.\n\nAn application that screens dangerous schemes on the raw input and then stores or renders `normalize(input)` or `resolve(base, input)` turns an inert string into an executable `javascript:`, `data:`, or `vbscript:` URL, a stored or reflected cross-site scripting vector in the consuming application. `equal()` also treats an encoded and a plain scheme as the same, which can bypass equality-based allowlists.\n\n### Patches\n\nUpgrade to `fast-uri` `2.4.8`, `3.1.9`, or `4.2.3`.\n\n### Workarounds\n\nReject input whose scheme part (before the first `:`, and before any `/`, `?`, or `#`) contains `%`. Alternatively, check `parse(x).scheme` against an allowlist after normalization and use that same parsed result rather than the raw string.\n\n## Affected packages\n\n- `fast-uri < 2.4.8`\n- `fast-uri >= 3.0.0, < 3.1.9`\n- `fast-uri >= 4.0.0, < 4.2.3`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `fast-uri 2.4.8`\n- `fast-uri 3.1.9`\n- `fast-uri 4.2.3`\n\n## Vendor advisories\n\n- **Red Hat VEX** · Moderate · affected: Cost Management On Premise, Cryostat 4, Migration Toolkit for Applications 8, Multicluster Engine for Kubernetes, Network Observability Operator, OpenShift Lightspeed, … · no fix planned: Red Hat Ansible Automation Platform 2, Red Hat Directory Server 11, Red Hat Directory Server 12, Red Hat Openshift Data Foundation 4, … · updated 2026-10-20 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-110306.json)","depth":"sunlit","depthScore":34,"depthScoreParts":{"impact":33.6,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}