CVE-2026-110306 fast-uri vulnerable to URI scheme spoofing via percent-encoded scheme decoding
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-110306?
CVE-2026-110306 is a medium-severity vulnerability in fast-uri, published on 20 Oct 2026.
Official description
fast-uri is a dependency-free RFC 3986 URI parser and serializer for Node.js. In versions before 2.4.8, from 3.0.0 through 3.1.8, and from 4.0.0 through 4.2.2, fast-uri percent-decodes the scheme component with the legacy global unescape() function before validating it, so an input whose decoded scheme is a dangerous token is emitted as a live scheme even though RFC 3986 does not allow percent-encoding in a scheme and no other parser accepts it. An application that screens dangerous schemes on the raw input and then stores or renders the normalized or resolved result can turn an inert string into an executable javascript, data, or vbscript URL, producing a stored or reflected cross-site scripting vector, and the equal() comparison treats an encoded and a plain scheme as the same, which can bypass equality-based allowlists. The issue is fixed in fast-uri 2.4.8, 3.1.9, and 4.2.3, and users should upgrade to one of these versions or later. As a workaround, reject input whose scheme part contains a percent sign, or check the parsed scheme against an allowlist after normalization and use that same parsed result rather than the raw string.
Which versions are affected by CVE-2026-110306?
6 open source packages ship an affected version, including fast-uri.
| Package | Affected | Fixed in |
|---|---|---|
fast-uri npm | All versions | 2.4.8 |
fast-uri npm | All versions | 2.4.8 |
fast-uri npm | From 3.0.0 | 3.1.9 |
fast-uri npm | From 3.0.0 | 3.1.9 |
fast-uri npm | From 4.0.0 | 4.2.3 |
fast-uri npm | From 4.0.0 | 4.2.3 |
How do I fix CVE-2026-110306?
Upgrade fast-uri to a fixed version for your release line: 2.4.8, 3.1.9 or 4.2.3.
Is CVE-2026-110306 being exploited?
There is no known exploitation of CVE-2026-110306 in the wild and no public exploit code.
Sources
Also known as CLSA-2026-1792517925, CLSA-2026-1792523667, CLSA-2026-1792574767, CLSA-2026-1793097094, DEBIAN-CVE-2026-110306, ECHO-30a5-67ec-a694 and 10 more.