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        "cveId": "CVE-2026-76169",
        "assignerOrgId": "ce714d77-add3-4f53-aff5-83d477b104bb",
        "state": "PUBLISHED",
        "assignerShortName": "openjs",
        "dateReserved": "2026-08-19T09:33:54.670Z",
        "datePublished": "2026-09-04T09:51:03.556Z",
        "dateUpdated": "2026-09-04T16:20:02.318Z"
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                    "lang": "en",
                    "value": "fastify versions >= 4.0.0 and before 5.12.2 can route a malformed URL sent under one plugin prefix to the custom not-found handler of a different sibling plugin, and invoke it without the preHandler hook declared for that handler. The internal not-found router for encapsulated handlers dispatches malformed paths through a single shared handler pointer before URL decoding, ignoring the prefix and skipping the selected handler's normal lifecycle. An unauthenticated attacker can therefore reach an authentication-protected private fallback through an unrelated public prefix and read its full response, bypassing the authentication hook and breaking prefix encapsulation. Users should upgrade to fastify 5.12.2 or later.",
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                            "value": "fastify versions >= 4.0.0 and before 5.12.2 can route a malformed URL sent under one plugin prefix to the custom not-found handler of a different sibling plugin, and invoke it without the preHandler hook declared for that handler. The internal not-found router for encapsulated handlers dispatches malformed paths through a single shared handler pointer before URL decoding, ignoring the prefix and skipping the selected handler's normal lifecycle. An unauthenticated attacker can therefore reach an authentication-protected private fallback through an unrelated public prefix and read its full response, bypassing the authentication hook and breaking prefix encapsulation. Users should upgrade to fastify 5.12.2 or later."
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                }
            ],
            "affected": [
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                    "vendor": "fastify",
                    "product": "fastify",
                    "defaultStatus": "unaffected",
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                            "versionType": "semver",
                            "status": "affected",
                            "version": "4.0.0",
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                            "version": "5.12.2"
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                    "packageURL": "pkg:npm/fastify"
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            "references": [
                {
                    "url": "https://github.com/fastify/fastify/security/advisories/GHSA-p68q-wchp-6fh7"
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                {
                    "url": "https://cna.openjsf.org/security-advisories.html"
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            "title": "fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers",
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                        "version": "3.1",
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                        "baseScore": 7.5,
                        "baseSeverity": "HIGH"
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            "problemTypes": [
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                    "descriptions": [
                        {
                            "cweId": "CWE-288",
                            "lang": "en",
                            "description": "CWE-288: Authentication Bypass Using an Alternate Path or Channel",
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                                "timestamp": "2026-09-04T16:18:32.577097Z",
                                "id": "CVE-2026-76169",
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