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CVE-2026-27959

CVE-2026-27959 · Koa has Host Header Injection via `ctx.hostname`

This page contains facts from public vulnerability sources. Check the original advisory before updating.

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.

CVSS 7.5 · High · EPSS 0.4% · Fix available

Published
Updated

Stack: node

Affected products and versions

  • koa

    Versions
    • >= 3.0.0, < 3.1.2: Affected
    • < 2.16.4: Affected

    No fix published

  • koa npm

    Affected ranges
    • SEMVER: ≥ 3.0.0, < 3.1.2

    Update to 3.1.2

  • koa npm

    Affected ranges
    • SEMVER: < 2.16.4

    Update to 2.16.4

Original sources

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