CVE-2026-27959
Koa has Host Header Injection via `ctx.hostname`
HIGH 8.2EPSS 0.5%
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.
- Affected
- koajs · koa
- CVSS v3.1 CNA
- 8.2 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N - CVSS v3.1 GITHUB
- 7.5 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N - EPSS
- 0.53% chance of exploitation in the next 30 days, 44th percentile
- Published
- 2026-02-26
- Updated
- 2026-07-15
Proof-of-concept exploits (1)
Security advisories
- koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm
- koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df