{"schemaVersion":3,"id":"CVE-2026-33804","aliases":["GHSA-v9ww-2j6r-98q6"],"status":"published","duplicateOf":null,"title":null,"description":"@fastify/middie versions 9.3.1 and earlier are vulnerable to middleware bypass when the deprecated Fastify ignoreDuplicateSlashes option is enabled. The middleware path matching logic does not account for duplicate slash normalization performed by Fastify's router, allowing requests with duplicate slashes to bypass middleware authentication and authorization checks. This only affects applications using the deprecated ignoreDuplicateSlashes option. Upgrade to @fastify/middie 9.3.2 to fix this issue. There are no workarounds other than disabling the ignoreDuplicateSlashes option.","dates":{"published":"2026-04-16T13:56:56.176Z","modified":"2026-04-16T14:41:48.659Z","reserved":null,"kevAdded":[],"kevDue":[]},"cvss":{"headline":{"score":9.1,"severity":"critical","version":"3.1","versionLabel":"v3.1","source":"NVD","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","computed":false,"selection":"backend-summary"},"metrics":[{"version":"3.1","versionLabel":"v3.1","source":"CVE.org","score":7.4,"severity":"high","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","exploitability":null,"impact":null,"computed":false},{"version":"3.1","versionLabel":"v3.1","source":"OSV · Npm","score":7.4,"severity":"high","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","exploitability":5.6,"impact":8.7,"computed":true},{"version":"3.1","versionLabel":"v3.1","source":"NVD","score":9.1,"severity":"critical","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","exploitability":null,"impact":null,"computed":false}]},"epss":{"probability":0.00491,"percentile":0.4094,"severity":"low","asOf":"2026-10-20T00:00:00.000Z","change":{"pp":0.21300000000000005,"baselineDate":"2026-09-20T00:00:00.000Z","baselineScore":0.00278},"history":[{"date":"2026-09-14T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-15T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-16T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-17T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-18T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-19T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-20T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-21T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-22T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-20T00:00:00.000Z","score":0.00491,"percentile":0.4094}],"last30":[{"date":"2026-09-20T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-21T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-22T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.00278,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.00491,"percentile":null},{"date":"2026-10-20T00:00:00.000Z","score":0.00491,"percentile":0.4094}]},"kev":{"state":"not-listed","entries":[],"listedCount":0,"totalCatalogs":3,"catalogs":[{"source":"cisa","label":"CISA","listed":false,"entry":null},{"source":"enisa","label":"ENISA","listed":false,"entry":null},{"source":"circl","label":"CIRCL","listed":false,"entry":null}]},"ransomware":{"state":"none-recorded","sources":[]},"exploits":[],"exploitCount":0,"weaknesses":[{"id":"CWE-436","name":"Interpretation Conflict","description":"Product A handles inputs or steps differently than Product B, which causes A to perform incorrect actions based on its perception of B's state.","type":"weakness","status":"Incomplete","abstraction":"Class","likelihoodOfExploit":null,"url":"https://cwe.mitre.org/data/definitions/436.html"}],"affected":[{"vendor":"fastify","product":"fastify\\/middie","name":"fastify\\/middie","label":"fastify\\/middie","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"< 9.3.2","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 9.3.2","eol":null,"hubHref":"/vendor/fastify/fastifymiddie"},{"vendor":"@fastify/middie","product":"@fastify/middie","name":"@fastify/middie","label":"@fastify/middie","ecosystem":null,"cpePart":"a","purl":null,"purlType":null,"versions":[{"text":"< 9.3.2","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 9.3.2","eol":null,"hubHref":"/vendor/fastifymiddie/fastifymiddie"},{"vendor":"@fastify","product":"middie","name":"@fastify/middie","label":"middie","ecosystem":"Npm","cpePart":null,"purl":"pkg:npm/@fastify/middie","purlType":"npm","versions":[{"text":"< 9.3.2","noFixRecorded":false,"fixedIn":null}],"versionsText":"< 9.3.2","eol":null,"hubHref":null}],"affectedCount":3,"eol":{"hasEol":false,"count":0},"references":[{"url":"https://github.com/fastify/middie/security/advisories/GHSA-v9ww-2j6r-98q6","label":"github.com/fastify/middie/security/advisories/GHSA-v9ww-2j6r-98q6","hostname":"github.com","tags":["WEB","Mitigation","Vendor Advisory"]},{"url":"https://cna.openjsf.org/security-advisories.html","label":"cna.openjsf.org/security-advisories.html","hostname":"cna.openjsf.org","tags":["WEB","Vendor Advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33804","label":"nvd.nist.gov/vuln/detail/CVE-2026-33804","hostname":"nvd.nist.gov","tags":["Advisory"]},{"url":"https://github.com/fastify/middie","label":"github.com/fastify/middie","hostname":"github.com","tags":["PACKAGE"]}],"lineage":{"upstream":[],"downstream":[],"duplicates":[],"related":[]},"timeline":[{"kind":"published","date":"2026-04-16T13:56:56.176Z","label":"Published","detail":"Vulnerability first disclosed.","source":null},{"kind":"modified","date":"2026-04-16T14:41:48.659Z","label":"Last modified","detail":"Vulnerability information updated.","source":null}],"risk":{"score":70,"level":"high","profile":"Default","thresholds":{"critical":75,"high":50,"medium":25,"low":10}},"meta":{"dataAsOf":"2026-10-20T20:56:38.450Z","stale":false,"partial":false}}