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High

fast-uri vulnerable to host confusion via failed IDN canonicalization

  • Disclosed: 21.07.2026
  • Updated: 11.10.2026 10:22

Impact

fast-uri versions >= 2.3.1, <= 4.0.0 fail to canonicalize Unicode/IDN hostnames for HTTP-family URLs. The IDN conversion path calls URL.domainToASCII(...) on the global WHATWG URL constructor, where that helper does not exist. The resulting TypeError is silently routed into parsed.error, but parse(), normalize(), and equal() all return with the host left in its original Unicode form.

For example, http://127。0。0。1/ is treated by fast-uri as host 127。0。0。1, while Node's WHATWG URL parser and fetch() canonicalize the same input to 127.0.0.1.

Applications that use fast-uri to enforce host-based policy (denylists, loopback filtering, redirect validation, outbound proxy routing) before passing the same URL into Node's URL or fetch() consumers see a policy/use desync and can be steered to an unintended destination.

Patches

Upgrade to fast-uri v4.0.1, v3.1.3, or v2.4.2

Workarounds

None. Upgrade to the patched version.

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
npm package fast-uri >= 4.0.0, < 4.0.1, >= 3.0.0, < 3.1.3, >= 2.3.1, < 2.4.2 4.0.1, 3.1.3, 2.4.2

References

CVSS score 7.5/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness (CWE)
CWE-436, CWE-551
Platform
npm
Package
fast-uri
Disclosed
21.07.2026
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-4c8g-83qw-93j6 - CC BY 4.0

Vulnerability history: fast-uri

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (13) in the archive
Total entries
13
First → latest
05.2026 09.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • High 11
  • Medium 2

Disclosures per year

Severity:
  1. fast-uri vulnerable to authority injection via an unvalidated port in serialize
    High · 7.5 CVE-2026-84292 < 2.4.6, >= 3.0.0, < 3.1.7, >= 4.0.0, < 4.1.4 2.4.6, 3.1.7, 4.1.4
  2. fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority
    High · 7.5 CVE-2026-84394 >= 2.4.5, < 2.4.6, >= 3.1.6, < 3.1.7, >= 4.1.3, < 4.1.4 2.4.6, 3.1.7, 4.1.4
  3. fast-uri vulnerable to host confusion via skipped IDN canonicalization on scheme-relative references
    High · 7.5 CVE-2026-75931 >= 2.4.2, < 2.4.5, >= 3.1.3, < 3.1.6, >= 4.0.1, < 4.1.3 2.4.5, 3.1.6, 4.1.3
  4. fast-uri vulnerable to server-side request forgery via malformed IPv6 normalization
    High · 7.5 CVE-2026-75975 >= 2.3.1, < 2.4.5, >= 3.0.0, < 3.1.6, >= 4.0.0, < 4.1.3 2.4.5, 3.1.6, 4.1.3
  5. fast-uri vulnerable to server-side request forgery via repeated hostname percent-decoding
    High · 7.5 CVE-2026-75899 >= 2.4.1, < 2.4.5, >= 3.1.2, < 3.1.6, >= 4.0.0, < 4.1.3 2.4.5, 3.1.6, 4.1.3
  6. fast-uri vulnerable to host confusion via percent-encoded scheme normalization
    High · 7.5 CVE-2026-76172 >= 2.3.1, < 2.4.5, >= 3.0.0, < 3.1.6, >= 4.0.0, < 4.1.3 2.4.5, 3.1.6, 4.1.3
  7. fast-uri vulnerable to host confusion via backslash authority introducer
    High · 7.5 CVE-2026-18446 < 2.4.4, >= 3.0.0, < 3.1.5, >= 4.0.0, < 4.1.2 2.4.4, 3.1.5, 4.1.2
  8. fast-uri vulnerable to host confusion via literal backslash authority delimiter
    High · 7.5 CVE-2026-16221 >= 2.3.1, < 2.4.3, >= 3.0.0, < 3.1.4, >= 4.0.0, < 4.1.1 2.4.3, 3.1.4, 4.1.1
  9. fast-uri vulnerable to host confusion via failed IDN canonicalization this entry
    High · 7.5 CVE-2026-13676 >= 4.0.0, < 4.0.1, >= 3.0.0, < 3.1.3, >= 2.3.1, < 2.4.2 4.0.1, 3.1.3, 2.4.2
  10. fast-uri vulnerable to host confusion via percent-encoded authority delimiters
    High · 7.5 CVE-2026-6322 >= 3.0.0, < 3.1.2, < 2.4.1 3.1.2, 2.4.1
  11. fast-uri vulnerable to path traversal via percent-encoded dot segments
    High · 7.5 CVE-2026-6321 >= 3.0.0, < 3.1.1, < 2.4.1 3.1.1, 2.4.1

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