{"id":"CVE-2026-33490","aliases":["GHSA-2j6q-whv2-gh6w"],"url":"https://o3.security/vulnerability/CVE-2026-33490","summary":"h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on Unrelated Prefix-Matching Routes","details":"H3 is a minimal H(TTP) framework. In versions 2.0.0-0 through 2.0.1-rc.16, the `mount()` method in h3 uses a simple `startsWith()` check to determine whether incoming requests fall under a mounted sub-application's path prefix. Because this check does not verify a path segment boundary (i.e., that the next character after the base is `/` or end-of-string), middleware registered on a mount like `/admin` will also execute for unrelated routes such as `/admin-public`, `/administrator`, or `/adminstuff`. This allows an attacker to trigger context-setting middleware on paths it was never intended to cover, potentially polluting request context with unintended privilege flags. Version 2.0.2-rc.17 contains a patch.","published":"2026-03-26T17:19:15.956Z","modified":"2026-07-15T01:48:53.060007478Z","cvss":{"score":3.7,"severity":"LOW","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"h3","fixedVersion":"2.0.1-rc.17"}],"fix":null,"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33490.json"},{"type":"ADVISORY","url":"https://github.com/h3js/h3/security/advisories/GHSA-2j6q-whv2-gh6w"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33490"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-15T01:48:53.060007478Z"}}