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CVE PROGRAM SOURCE RECORD7.5 High

CVE-2026-27959

Koa has Host Header Injection via `ctx.hostname`

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Status
Published
Published
Updated
Assigning organization
GitHub_M

Description

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 products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

koajs koa

  • >= 3.0.0, < 3.1.2affected
  • < 2.16.4affected

References