# CVE-2026-110306: fast-uri vulnerable to URI scheme spoofing via percent-encoded scheme decoding


- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 20 Oct 2026
- **Updated:** 20 Oct 2026
- **Also known as:** CLSA-2026-1792517925, CLSA-2026-1792523667, CLSA-2026-1792574767, CLSA-2026-1793097094, DEBIAN-CVE-2026-110306, ECHO-30a5-67ec-a694, GHSA-w74x-v6f9-j3xg, MINI-56q8-hcwx-p424, MINI-59jm-cxgr-fjjw, MINI-6jhg-3fm2-g98h, MINI-6vf9-qv49-2qvc, MINI-8jp6-rjx7-q8rm, MINI-m7fh-6732-xgxw, MINI-qf3g-7fp3-gm7p, MINI-v7g7-4j48-9x4h, UBUNTU-CVE-2026-110306

## 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.

Weakness: CWE-180 (Incorrect Behavior Order: Validate Before Canonicalize), CWE-172 (Improper Encoding or Decoding of Data)

## Which versions are affected by CVE-2026-110306?

6 open source packages ship an affected version, including fast-uri.


| Package | Ecosystem | 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-110306 and fix it if it is affected.

What it is: CVE-2026-110306 is a medium-severity vulnerability in fast-uri, published on 20 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-110306 in the wild and no public exploit code.

Affected packages and fixed versions:
- fast-uri (npm): affected all versions; fixed in 2.4.8
- fast-uri (npm): affected all versions; fixed in 2.4.8
- fast-uri (npm): affected from 3.0.0; fixed in 3.1.9
- fast-uri (npm): affected from 3.0.0; fixed in 3.1.9
- fast-uri (npm): affected from 4.0.0; fixed in 4.2.3
- fast-uri (npm): affected from 4.0.0; fixed in 4.2.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-110306/ (Markdown: https://insights.sbomify.com/CVE-2026-110306/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-110306
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-110306
- OSV: https://osv.dev/vulnerability/CVE-2026-110306

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-110306/
Summaries are generated and may contain mistakes; the official description above is the record.