GHSA-7p8r-x3mc-p8w7 CVE-2026-18446
fast-uri vulnerable to host confusion via backslash authority introducer
- Severity
- 7.5 / 10
- High · CVSS 3.1
- Exploit chance (EPSS)
- 0.38%
- Chance of exploitation in the next 30 days. Higher than 32.01% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-436 Interpretation Conflict
- Fix
2.4.4- Upgrade fast-uri to this version or later
Description
Impact
fast-uri v4.1.1 and earlier require a literal // to recognize a URI authority, so a reference that uses \\, /\, or \/ as the authority introducer (in place of //, after an optional scheme) is parsed with no authority: the sequence and everything after it fold into the path. Node's native WHATWG URL (used by fetch(), undici, and Node's http/https clients) instead treats \ as interchangeable with / for special schemes (http, https, ws, wss, ftp, file), so the two parsers extract different hosts from the same input.
For example, fast-uri resolves \\evil.com/path against base https://allowed.com/ to https://allowed.com/%5C%5Cevil.com/path (confined to the trusted host), while Node's WHATWG URL resolves the same reference to https://evil.com/path.
Applications that use fast-uri to enforce host-based policy (allowlists, denylists, loopback/SSRF 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 v4.1.2, v3.1.5, v2.4.4.
Workarounds
None. Upgrade to the patched version.
Affected versions
npm
| Package | Vulnerable | Fixed in |
|---|---|---|
| fast-uri | < 2.4.4 |
2.4.4 |
| fast-uri | >= 3.0.0, < 3.1.5 |
3.1.5 |
| fast-uri | >= 4.0.0, < 4.1.2 |
4.1.2 |
| fast-uri | < 2.4.4 |
2.4.4 |
| fast-uri | >= 3.0.0, < 3.1.5 |
3.1.5 |
| fast-uri | >= 4.0.0, < 4.1.2 |
4.1.2 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
fast-uri npm → 2.4.4
- npm
npm install fast-uri@2.4.4- yarn
yarn add fast-uri@2.4.4- pnpm
pnpm add fast-uri@2.4.4
Severity breakdown
CVSS 3.1 7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
Weakness
CWE-436: Interpretation Conflict
Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.
References
Advisories
Fixes and patches
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-333x-w4r6-6crp fast-uri vulnerable to scheme injection via an unescaped first-segment colon in suffix references | Low | Also affects fast-uri |
| GHSA-w74x-v6f9-j3xg fast-uri vulnerable to URI scheme spoofing via percent-encoded scheme decoding | Medium | Also affects fast-uri |
| GHSA-wjr9-j795-jxcr fast-uri vulnerable to host confusion via unchecked WHATWG host canonicalization | Medium | Also affects fast-uri |
| GHSA-xhq7-xmqj-769h fast-uri vulnerable to improper path equivalence in relative reference normalization | Low | Also affects fast-uri |
| GHSA-jvvf-x445-j334 fast-uri vulnerable to mailto header injection via percent-encoded field-name desynchronization | Medium | Also affects fast-uri |
| GHSA-hrr3-gc8f-f4qj fast-uri vulnerable to inconsistent host case normalization via percent-encoded octets | Medium | Also affects fast-uri |
| GHSA-58mr-gqgx-xq4g fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority | High | Also affects fast-uri |
| GHSA-qw65-cvwx-89v3 fast-uri vulnerable to authority injection via an unvalidated port in serialize | High | Also affects fast-uri |
Credits: UlisesGascon, iaohkut-from-NightWolf-Team, mcollina
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