h3 has a middleware bypass with one gadget

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.4 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

• CVE-2026-33131: 0.40% estimated exploitation activity in the next 30 days; percentile 33.76 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

H3 NodeRequestUrl bugs Vulnerable pieces of code : The middleware is super safe now with just a logger and a middleware to block internal access. But there's one problems here at the logger . When it log out the or or It will lead to trigger one specials method The NodeRequestUrl is extends from FastURL so when we just access or trying to dump all data of this class . This function will be triggered !! And as debugging , the this.#url is null and will reach to this code : Where is the this.href comes from ? Because the this.#url is still null so this.#href is built up by : Yeah and this is untrusted data go . An attacker can pollute the Host header from requests lead overwrite the event.url . Middleware bypass What can be done with overwriting the event.url? Audit the code we can easily realize that the routeHanlder is found before running any middlewares So the handleRoute is fixed but when checking with middleware it check with the spoofed one lead to MIDDLEWARE BYPASS We have this…

Published by the source

18 Mar 2026, 16:18 UTC

Last modified by the source

20 Mar 2026, 21:59 UTC

Source last checked

26 Oct 2026, 12:46 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-3vj8-jmxq-cgj5

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-3vj8-jmxq-cgj5

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# Patch Next advisory brief: CVE-2026-33131

Advisory: h3 has a middleware bypass with one gadget
IDs: CVE-2026-33131, GHSA-3vj8-jmxq-cgj5
Record: https://patchnext.com/advisories/cve-2026-33131 (revision 2, source checked 26 Oct 2026, 12:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: h3 2.0.1-rc.15. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm h3: affected >= 2.0.0-0, < 2.0.1-rc.15; fixed in 2.0.1-rc.15

## Suggested inspection (read-only)
- `npm ls h3 --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on h3.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-3vj8-jmxq-cgj5 (OSV record GHSA-3vj8-jmxq-cgj5 lists affected ranges: npm h3 >=2.0.0-0 <2.0.1-rc.15 (fixed))
- Verified: https://github.com/advisories/GHSA-3vj8-jmxq-cgj5 (GitHub-reviewed advisory GHSA-3vj8-jmxq-cgj5 lists affected ranges: npm h3 >=2.0.0-0 <2.0.1-rc.15)

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