{"id":"GHSA-8j4g-w8fx-2239","summary":"Hono: ReDoS in CORS middleware via Access-Control-Request-Headers","details":"### Summary\n\nThe built-in CORS middleware (`hono/cors`) parses the attacker-controlled `Access-Control-Request-Headers` request header during a preflight (`OPTIONS`) request using a regular expression whose running time is quadratic in the input length. A single request carrying a long run of whitespace can consume seconds of CPU, and repeated requests can render the service unresponsive. This parsing runs under the default configuration.\n\n### Details\n\nOn a CORS preflight, when `allowHeaders` is not configured - the default - the middleware reflects and parses the `Access-Control-Request-Headers` value. The parser used a whitespace-tolerant regular expression whose backtracking makes the work grow quadratically (O(n²)) with the length of the value when it contains a long whitespace sequence without a delimiter.\n\nBecause the header value is bounded only by the deployment's maximum HTTP header size, a single preflight can block request processing for a noticeable amount of time; on runtimes that share one execution thread across requests, this stalls concurrent requests as well. No authentication, special origin, or user interaction is required.\n\nThis issue arises for any application using `cors()` with the default (or an empty) `allowHeaders`. Applications that set a non-empty `allowHeaders` do not reach the affected path.\n\n### Impact\n\nAn unauthenticated attacker can send preflight requests that each consume disproportionate CPU relative to their size, degrading or denying service. This is a denial-of-service issue only; it does not expose or modify data.","aliases":["CVE-2026-69207"],"modified":"2026-08-03T20:41:10.342578Z","published":"2026-08-03T20:23:30Z","database_specific":{"github_reviewed_at":"2026-08-03T20:23:30Z","nvd_published_at":null,"cwe_ids":["CWE-1333"],"severity":"MODERATE","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/honojs/hono/security/advisories/GHSA-8j4g-w8fx-2239"},{"type":"WEB","url":"https://github.com/honojs/hono/commit/93fc250d8b4df58ea542cb945171de8013d5e6d5"},{"type":"PACKAGE","url":"https://github.com/honojs/hono"},{"type":"WEB","url":"https://github.com/honojs/hono/releases/tag/v4.12.34"}],"affected":[{"package":{"name":"hono","ecosystem":"npm","purl":"pkg:npm/hono"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"4.12.34"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-8j4g-w8fx-2239/GHSA-8j4g-w8fx-2239.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"}]}