{"id":"CVE-2026-27959","aliases":["GHSA-7gcc-r8m5-44qm"],"url":"https://o3.security/vulnerability/CVE-2026-27959","summary":"Koa has Host Header Injection via `ctx.hostname`","details":"Koa is middleware for Node.js using ES2017 async functions. Prior to versions 3.1.2 and 2.16.4, Koa's `ctx.hostname` API performs naive parsing of the HTTP Host header, extracting everything before the first colon without validating the input conforms to RFC 3986 hostname syntax. When a malformed Host header containing a `@` symbol is received, `ctx.hostname` returns `evil[.]com` - an attacker-controlled value. Applications using `ctx.hostname` for URL generation, password reset links, email verification URLs, or routing decisions are vulnerable to Host header injection attacks. Versions 3.1.2 and 2.16.4 fix the issue.","published":"2026-02-26T01:45:45.668Z","modified":"2026-07-16T03:31:09.649814721Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"koa","fixedVersion":"3.1.2"},{"ecosystem":"npm","name":"koa","fixedVersion":"2.16.4"}],"fix":{"url":"https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df","label":"koajs/koa@55ab9ba"},"references":[{"type":"WEB","url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27959.json"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:10184"},{"type":"ADVISORY","url":"https://access.redhat.com/errata/RHSA-2026:7249"},{"type":"ADVISORY","url":"https://access.redhat.com/security/cve/CVE-2026-27959"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27959.json"},{"type":"ADVISORY","url":"https://github.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-27959"},{"type":"REPORT","url":"https://bugzilla.redhat.com/show_bug.cgi?id=2442928"},{"type":"FIX","url":"https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df"},{"type":"FIX","url":"https://github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-07-16T03:31:09.649814721Z"}}