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CVE-2026-33131— h3 has a middleware bypass with one gadget

Quick assessment

Affected
h3js h3
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

H3是H3开源的一个HTTP框架。 H3 2.0.0-0至2.0.1-rc.14版本存在安全漏洞，该漏洞源于NodeRequestUrl存在Host标头欺骗，可能导致中间件绕过。

CVSS 7.4 · High EPSS 0.44% · P36
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I. Basic Information for CVE-2026-33131

Vulnerability Information
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Vulnerability Title
h3 has a middleware bypass with one gadget
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
使用欺骗进行的认证绕过
Source: CVE Program / CVE List V5
Vulnerability Title
H3 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
H3是H3开源的一个HTTP框架。 H3 2.0.0-0至2.0.1-rc.14版本存在安全漏洞，该漏洞源于NodeRequestUrl存在Host标头欺骗，可能导致中间件绕过。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
h3js h3 >= 2.0.0-0, < 2.0.1-rc.15 -

II. Public POCs for CVE-2026-33131

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III. Intelligence Information for CVE-2026-33131

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Vendor Advisories for CVE-2026-33131 (1)

Same Patch Batch · h3js · 2026-03-20 · 3 CVEs total

CVE-2026-33128 7.5 HIGH h3 has a Server-Sent Events Injection via Unsanitized Newlines in Event Stream Fields
CVE-2026-33129 5.9 MEDIUM h3 has an observable timing discrepancy in basic auth utils

IV. Related Vulnerabilities

Same product: h3
Same vendor: h3js
Same weakness: CWE-290

V. Comments for CVE-2026-33131

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