fast-uri vulnerable to improper path equivalence in relative reference normalization

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, the normalize() and serialize() functions apply RFC 3986 dot-segment removal to the path of a relative-path reference, even though that algorithm is defined only for the merged target path during resolution, so a leading parent-directory segment can be dropped and a document-relative reference can become root-relative. An application that normalizes an attacker-supplied or user-supplied relative reference and then resolves it, or uses it as a cache, deduplication, or authorization key, can have the reference escape its intended directory and point at a different resource. 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, resolve a relative reference against its absolute base first and normalize the absolute result instead of normalizing the reference beforehand.

Timeline

1. Oct 20, 2026, 6:56 AM UTCCVE published
2. Oct 20, 2026, 4:07 PM UTCCISA SSVC assessment

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

3. Oct 20, 2026, 4:07 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