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High

fast-uri vulnerable to host confusion via percent-encoded authority delimiters

  • Disclosed: 08.05.2026
  • Updated: 11.10.2026 10:22

Impact

fast-uri v3.1.1 and earlier decodes percent-encoded authority delimiters (%40 as @, %3A as :) inside the host component and serializes them back as raw characters. This changes the URI structure, turning a hostname into userinfo plus a different host.

For example, http://trusted.com%40evil.com/ normalizes to http://trusted.com@evil.com/, which reparses as host evil.com with userinfo trusted.com.

Applications that normalize untrusted URLs before host allowlist checks, redirect validation, or outbound request routing can be steered to a different authority than the original URL appeared to contain.

Patches

Upgrade to fast-uri >= 3.1.2, or if you are in the v2.x release line, v2.4.1

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 >= 3.0.0, < 3.1.2, < 2.4.1 3.1.2, 2.4.1

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-140, CWE-436
Platform
npm
Package
fast-uri
Disclosed
08.05.2026
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-v39h-62p7-jpjc - 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
    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 this entry
    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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