h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on Unrelated Prefix-Matching Routes_CVE-2026-33490

{
    "lastseen": "",
    "description": "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": "2026-03-26T18:23:39.653Z",
    "type": "cve",
    "title": "h3: Missing Path Segment Boundary Check in `mount()` Causes Middleware Execution on Unrelated Prefix-Matching Routes",
    "source": "GitHub_M",
    "references": "https://github.com/h3js/h3/security/advisories/GHSA-2j6q-whv2-gh6w",
    "id": "CVE-2026-33490",
    "bulletinFamily": "",
    "cwe": [
        "CWE-706"
    ],
    "cvelist": null,
    "sourceData": "h3js h3 >= 2.0.1-alpha.0, < 2.0.1-rc.17",
    "sourceHref": "",
    "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",
        "version": "3.1"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
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            "privilegesRequired": "",
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            "confidentialityImpact": "",
            "integrityImpact": "",
            "availabilityImpact": ""
        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "h3",
    "version": ">= 2.0.1-alpha.0, < 2.0.1-rc.17",
    "vendor": "h3js",
    "ai_description": "",
    "ai_severity": "",
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    "ai_score": 0
}