{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-16732","assignerOrgId":"ce714d77-add3-4f53-aff5-83d477b104bb","state":"PUBLISHED","assignerShortName":"openjs","dateReserved":"2026-07-23T07:30:53.415Z","datePublished":"2026-08-18T20:30:22.592Z","dateUpdated":"2026-08-19T13:16:06.497Z"},"containers":{"cna":{"providerMetadata":{"orgId":"ce714d77-add3-4f53-aff5-83d477b104bb","shortName":"openjs","dateUpdated":"2026-08-18T20:30:22.592Z"},"descriptions":[{"lang":"en","value":"fastify is a fast and low overhead web framework for Node.js. Impact: the fix for CVE-2026-3635 added a guard on the forwarded-header reads used to derive the request host, protocol, hostname, ip, and ips values, checking the connecting address. That guard closes the IP, CIDR, and custom-function forms of trustProxy correctly, because those forms compile to predicates that inspect the connecting address. The hop-count form, where trustProxy is set to a number, compiles to a predicate that structurally ignores the address, so the guard is always satisfied for any hop count of one or more. Applications configured with a numeric trustProxy value, such as trustProxy set to 1 for a single reverse proxy, remain vulnerable: an attacker who can reach the Fastify origin directly, bypassing the front-facing proxy, can spoof the forwarded request fields exactly as in the unpatched version. The impact class matches the parent CVE-2026-3635, including host injection in generated URLs, HTTPS-enforcement bypass, secure-cookie and CSRF-origin bypass, and host-based routing and cache poisoning. Affected versions are fastify from 5.8.3 up to but not including 5.12.1. Patches: patched in fastify 5.12.1, where the numeric form of trustProxy is disabled at runtime and removed from the TypeScript type union. Workarounds: migrate to an IP, CIDR, or custom-function trustProxy value that validates the connecting address, and ensure the Fastify origin is only reachable through the trusted proxy chain.","supportingMedia":[{"type":"text/html","base64":false,"value":"fastify is a fast and low overhead web framework for Node.js. Impact: the fix for CVE-2026-3635 added a guard on the forwarded-header reads used to derive the request host, protocol, hostname, ip, and ips values, checking the connecting address. That guard closes the IP, CIDR, and custom-function forms of trustProxy correctly, because those forms compile to predicates that inspect the connecting address. The hop-count form, where trustProxy is set to a number, compiles to a predicate that structurally ignores the address, so the guard is always satisfied for any hop count of one or more. Applications configured with a numeric trustProxy value, such as trustProxy set to 1 for a single reverse proxy, remain vulnerable: an attacker who can reach the Fastify origin directly, bypassing the front-facing proxy, can spoof the forwarded request fields exactly as in the unpatched version. The impact class matches the parent CVE-2026-3635, including host injection in generated URLs, HTTPS-enforcement bypass, secure-cookie and CSRF-origin bypass, and host-based routing and cache poisoning. Affected versions are fastify from 5.8.3 up to but not including 5.12.1. Patches: patched in fastify 5.12.1, where the numeric form of trustProxy is disabled at runtime and removed from the TypeScript type union. Workarounds: migrate to an IP, CIDR, or custom-function trustProxy value that validates the connecting address, and ensure the Fastify origin is only reachable through the trusted proxy chain."}]}],"affected":[{"vendor":"fastify","product":"fastify","defaultStatus":"unaffected","versions":[{"versionType":"semver","status":"affected","version":"5.8.3","lessThan":"5.12.1"},{"versionType":"semver","status":"unaffected","version":"5.12.1"}],"packageURL":"pkg:npm/fastify"}],"references":[{"url":"https://github.com/fastify/fastify/security/advisories/GHSA-3m5p-2c4r-xxw2"},{"url":"https://cna.openjsf.org/security-advisories.html"}],"credits":[{"lang":"en","type":"reporter","value":"alimony"},{"lang":"en","type":"remediation developer","value":"mcollina"},{"lang":"en","type":"remediation reviewer","value":"climba03003"},{"lang":"en","type":"remediation reviewer","value":"UlisesGascon"}],"title":"fastify vulnerable to X-Forwarded-* spoofing under trustProxy hop-count","metrics":[{"format":"CVSS","cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:N/A:N","baseScore":6.1,"baseSeverity":"MEDIUM"},"scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-348","lang":"en","description":"CWE-348: Use of Less Trusted Source","type":"CWE"}]}],"x_generator":{"engine":"cve-kit 1.0.0"}},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-19T13:15:46.091425Z","id":"CVE-2026-16732","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-08-19T13:16:06.497Z"}}]}}