fast-uri vulnerable to scheme injection via an unescaped first-segment colon in suffix references

Summary

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.

Timeline

1. Oct 20, 2026, 7:06 AM UTCCVE published
2. Oct 20, 2026, 7:14 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Oct 20, 2026, 7:14 PM UTCRecord last updated
4. Oct 22, 2026, 9:34 PM UTCFirst seen by cve.now

Affected versions

• fast-uri 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-urinpm

  fixed in 2.4.8

• fast-urinpm

  From 3.0.0 · fixed in 3.1.9

• fast-urinpm

  From 4.0.0 · fixed in 4.2.3

References 2