CVE-2026-33131

The record

H3 is a minimal H(TTP) framework. Versions 2.0.0-0 through 2.0.1-rc.14 contain a Host header spoofing vulnerability in the NodeRequestUrl (which extends FastURL) which allows middleware bypass. When event.url, event.url.hostname, or event.url._url is accessed, such as in a logging middleware, the _url getter constructs a URL from untrusted data, including the user-controlled Host header. Because H3's router resolves the route handler before middleware runs, an attacker can supply a crafted Host header (e.g., Host: localhost:3000/abchehe?) to make the middleware path check fail while the route handler still matches, effectively bypassing authentication or authorization middleware. This affects any application built on H3 (including Nitro/Nuxt) that accesses event.url properties in middleware guarding sensitive routes. The issue requires an immediate fix to prevent FastURL.href from being constructed with unsanitized, attacker-controlled input. Version 2.0.1-rc.15 contains a patch for this issue.

Affected packages

Related vulnerabilities

• GHSA-3vj8-jmxq-cgj5 h3 has a middleware bypass with one gadget Same vulnerability
• CVE-2026-33490 H3 is a minimal H(TTP) framework. Also affects h3
• GHSA-fp4x-ggrf-wmc6 H3 has an Open Redirect via Protocol-Relative Path in redirectBack() Referer Validation Also affects h3
• GHSA-q5pr-72pq-83v3 H3: Unbounded Chunked Cookie Count in Session Cleanup Loop may Lead to Denial of Service Also affects h3
• GHSA-4hxc-9384-m385 h3: SSE Event Injection via Unsanitized Carriage Return (`\r`) in EventStream Data and… Also affects h3
• GHSA-2j6q-whv2-gh6w h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on… Also affects h3
• GHSA-72gr-qfp7-vwhw h3: Double Decoding in `serveStatic` Bypasses `resolveDotSegments` Path Traversal… Also affects h3
• CVE-2026-33128 H3 is a minimal H(TTP) framework. Also affects h3