{"id":"CVE-2026-39409","aliases":["GHSA-xpcf-pg52-r92g"],"url":"https://o3.security/vulnerability/CVE-2026-39409","summary":"Hono has incorrect IP matching in ipRestriction() for IPv4-mapped IPv6 addresses","details":"## Summary\n\n`ipRestriction()` does not canonicalize IPv4-mapped IPv6 client addresses (e.g. `::ffff:127.0.0.1`) before applying IPv4 allow or deny rules. In environments such as Node.js dual-stack, this can cause IPv4 rules to fail to match, leading to unintended authorization behavior.\n\n## Details\n\nThe middleware classifies client addresses based on their textual form. Addresses containing \"`:`\" are treated as IPv6, including IPv4-mapped IPv6 addresses such as `::ffff:127.0.0.1`. These addresses are not normalized to IPv4 before matching.\n\nAs a result:\n\n* IPv4 static rules (e.g. `127.0.0.1`) do not match because the raw string differs\n* IPv4 CIDR rules (e.g. `127.0.0.0/8`, `10.0.0.0/8`) are skipped because the address is treated as IPv6\n\nFor example, with:\n\n`denyList: ['127.0.0.1']`\n\na request from `127.0.0.1` may be represented as `::ffff:127.0.0.1` and bypass the deny rule.\n\nThis behavior commonly occurs in Node.js environments where IPv4 clients are exposed as IPv4-mapped IPv6 addresses.\n\n## Impact\n\nApplications that rely on IPv4-based `ipRestriction()` rules may incorrectly allow or deny requests.\n\nIn affected deployments, a denied IPv4 client may bypass access restrictions. Conversely, legitimate clients may be rejected when using IPv4 allow lists.","published":"2026-04-08T14:43:36.476Z","modified":"2026-08-12T03:51:41.994017423Z","cvss":null,"epss":{"score":0.00343,"percentile":0.2771,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"hono","fixedVersion":"4.12.12"}],"fix":{"url":"https://github.com/honojs/hono/commit/48fa2233bc092f650119f42df043050737cabf39","label":"honojs/hono@48fa223"},"references":[{"type":"WEB","url":"https://github.com/honojs/hono/releases/tag/v4.12.12"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/39xxx/CVE-2026-39409.json"},{"type":"ADVISORY","url":"https://github.com/honojs/hono/security/advisories/GHSA-xpcf-pg52-r92g"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-39409"},{"type":"FIX","url":"https://github.com/honojs/hono/commit/48fa2233bc092f650119f42df043050737cabf39"},{"type":"PACKAGE","url":"https://github.com/honojs/hono"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:41.994017423Z"}}