fast-uri vulnerable to scheme injection via an unescaped first-segment colon in suffix references
CVE-2026-110725
Impact fast-uri's serialize(), normalize(), and resolve(), when called with the non-default option reference: 'suffix' on a reference that has no authority, emit a relative reference whose first path segment contains a bare colon without escaping it. RFC 3986 section 3.3 requires the first segment of a path-noscheme reference not to contain a colon, precisely because a bare colon makes the string reparse as an absolute URI with a scheme. fast-uri's default serialization escapes that colon, but the suffix path does not. For example, normalize('javascript:alert(1)', { reference: 'suffix' }) returns javascript:alert(1), which reparses as a live javascript: scheme; data: and vbscript: behave the same. Applications that serialize or normalize a relative reference with reference: 'suffix' and then treat the result as a URI can turn inert input into a live javascript:, data:, or vbscript: URL (a cross-site scripting vector), and equal() can conflate a scheme-bearing reference with a relative one. Exposure is limited to applications that use the non-default reference: 'suffix' option. Patches Upgrade to fast-uri 2.4.8, 3.1.9, or 4.2.3. Workarounds Do not use the reference: 'suffix' option…
Assessment
- CVSS
- 3.7 (v3.1)
- Severity
- Low
- EPSS
- 0.00302% chance of exploitation in the next 30 days
- Known exploited
- Not listed in CISA KEV
- Exploit availability
- Nothing found in Exploit-DB, Metasploit, Nuclei or public PoC repositories
- Published
- 23 October 2026
- Last updated
- 23 October 2026
- Affected
- npm · fast-uri
- Weakness
- CWE-116, CWE-41
CVSS vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
At the source
References
- https://github.com/fastify/fast-uri/security/advisories/GHSA-333x-w4r6-6crp
- https://nvd.nist.gov/vuln/detail/CVE-2026-110725
- https://github.com/fastify/fast-uri/commit/39e6493c1356f30a0084171627eb266786e1620e
- https://github.com/fastify/fast-uri/commit/a9b8d67353630aab053cd727cf629023dd018d2b
- https://cna.openjsf.org/security-advisories.html
- https://github.com/fastify/fast-uri/releases/tag/v2.4.8
- https://github.com/fastify/fast-uri/releases/tag/v3.1.9
- https://github.com/fastify/fast-uri/releases/tag/v4.2.3
- https://github.com/advisories/GHSA-333x-w4r6-6crp
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