CVE-2026-75931 PUBLISHED

fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references

Assigner: openjs
Reserved: 18.08.2026 Published: 24.08.2026 Updated: 24.08.2026

fast-uri is a URI parser for Node.js. It canonicalizes a host to its ASCII form only when the input carries an explicit scheme, so a scheme-relative reference such as a host preceded by two slashes is returned with its host verbatim and no error set. As a result fast-uri's own entry points disagree with each other: parse, resolve, normalize, and equal can yield different hosts for the same input depending only on whether a scheme is written out, and equal can return opposite verdicts for the same pair of hosts. An application that extracts a host with fast-uri to check it against a policy list and then resolves the same reference can make its decision on one host while the destination is another, enabling host confusion and policy bypass. The affected versions are 2.4.2 up to but not including 2.4.5, 3.1.3 up to but not including 3.1.6, and 4.0.1 up to but not including 4.1.3. The issue is fixed in 2.4.5, 3.1.6, and 4.1.3, which canonicalize the host consistently across the resolve path. Users should upgrade to a patched version.

Metrics

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CVSS Score: 7.5

Product Status

Vendor fast-uri
Product fast-uri
Versions Default: unaffected
  • affected from 2.4.2 to 2.4.5 (excl.)
  • Version 2.4.5 is unaffected
  • affected from 3.1.3 to 3.1.6 (excl.)
  • Version 3.1.6 is unaffected
  • affected from 4.0.1 to 4.1.3 (excl.)
  • Version 4.1.3 is unaffected

Credits

  • baeseungwon1010 reporter
  • mcollina remediation developer
  • UlisesGascon remediation reviewer

References

Problem Types

  • CWE-436: Interpretation Conflict CWE