CVE-2026-86472Medium· 4.8▾ Sunlitfast-uri is a dependency-free RFC 3986 URI parser for Node.js, used by Fastify and ajv. In versions before 2.4.7, from 3.0.0 through 3.1.7, and from 4.0.0 through 4.1.4, fast-uri folds the host to lowercase before it percent-decodes the …
▾ Sunlit zone — Low / medium · no exploitation signal
impact 26.4 · likelihood 0.1 · exploitation 0
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Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake.
Exploit-prediction probability, daily snapshots since Sep 19.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
Last analysed / modified upstream
0.2%
0.2% → 0.3%
fast-uri is a dependency-free RFC 3986 URI parser for Node.js, used by Fastify and ajv. In versions before 2.4.7, from 3.0.0 through 3.1.7, and from 4.0.0 through 4.1.4, fast-uri folds the host to lowercase before it percent-decodes the host, so a percent-encoded uppercase octet such as %41 decodes to a literal A that is never folded. For a scheme-relative reference such as //host there is no scheme, so the host canonicalization that would normally repair this does not run, and parse, normalize, and equal then disagree on the same host. An application that makes a case-sensitive host decision on fast-uri output, for example a host allowlist or denylist that compares the parsed host or uses equal, can be steered past the check with a percent-encoded uppercase octet, and because hostnames are case-insensitive in DNS and HTTP the evading spelling still reaches the host the check meant to gate. The issue is fixed in fast-uri 2.4.7, 3.1.8, and 4.1.5, and users should upgrade to one of those versions or later. As a workaround, compare hosts case-insensitively by lowercasing the parsed host before any allowlist or denylist decision.
Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Affected packages:
fast-uri < 2.4.7fast-uri >= 3.0.0, < 3.1.8fast-uri >= 4.0.0, < 4.1.5Patched in:
fast-uri 2.4.7fast-uri 3.1.8fast-uri 4.1.5Connected by shared product, vendor, weakness, or advisory.
CVE-2026-86818Medium· 4.8fast-uri is a dependency-free RFC 3986 URI parser for Node.js, used by Fastify and ajv, that added a mailto scheme parser in version 4.1.3
CVE-2026-110095Low· 3.7fast-uri vulnerable to improper path equivalence in relative reference normalization
CVE-2026-110180Medium· 4.8fast-uri vulnerable to host confusion via unchecked WHATWG host canonicalization
CVE-2026-110725Low· 3.7fast-uri vulnerable to scheme injection via an unescaped first-segment colon in suffix references
CVE-2026-110306Medium· 6.1fast-uri vulnerable to URI scheme spoofing via percent-encoded scheme decoding
CVE-2026-84292High· 7.5fast-uri serializes the port component of a URI without validating it