{"id":"CVE-2026-71848","aliases":["GHSA-54fx-42gc-7vw4"],"url":"https://o3.security/vulnerability/CVE-2026-71848","summary":"Hono: Algorithmic Complexity DoS in Language Middleware","details":"### Summary\n\nThe `languageDetector` middleware is vulnerable to algorithmic complexity denial of service when processing a crafted language tag containing a large number of hyphen-separated subtags.\n\n### Details\n\nTo implement progressive language-tag truncation, `normalizeLanguage()` repeatedly calls `parts.slice(0, i).join('-')` for every possible prefix. The total amount of string processing grows quadratically with the number of subtags.\n\nLanguage values may come from a query parameter, cookie, `Accept-Language` header, or URL path, depending on the detector configuration. The default detector order enables query-string, cookie, and header detection, so applications using `languageDetector()` may expose this processing to unauthenticated requests.\n\nRequest-size limits reduce the maximum cost of a single request but do not eliminate the issue. Inputs accepted by common JavaScript runtimes can still cause noticeable synchronous event-loop blocking.\n\n### Impact\n\nAn attacker may repeatedly send requests containing long, hyphen-separated language tags, causing excessive CPU consumption and preventing unrelated requests from being processed.\n\nThe practical impact depends on the runtime's request-size limits, reverse-proxy configuration, and the detectors enabled by the application.\n\n### Resolution\n\nThe progressive lookup should avoid reconstructing every shorter prefix. The implementation can instead inspect the configured supported languages and select the longest value that matches the input at a hyphen boundary.","published":"2026-08-07T18:36:16.872Z","modified":"2026-09-11T03:48:34.650935697Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"hono","fixedVersion":"4.12.34"}],"fix":{"url":"https://github.com/honojs/hono/commit/f70e2c31684387b3231cc38512a31df6ca76a1c7","label":"honojs/hono@f70e2c3"},"references":[{"type":"WEB","url":"https://github.com/honojs/hono/releases/tag/v4.12.34"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/71xxx/CVE-2026-71848.json"},{"type":"ADVISORY","url":"https://github.com/honojs/hono/security/advisories/GHSA-54fx-42gc-7vw4"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-71848"},{"type":"FIX","url":"https://github.com/honojs/hono/commit/f70e2c31684387b3231cc38512a31df6ca76a1c7"},{"type":"PACKAGE","url":"https://github.com/honojs/hono"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-11T03:48:34.650935697Z"}}