CVE-2026-27959
Koa has Host Header Injection via `ctx.hostname`
- State
- Published
- Severity
- 7.5 High
- Published
- Feb 26, 2026
- Updated
- Jul 15, 2026
- Reserved
- Feb 25, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 7.5 High | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N | GitHub_M |
| 3.1 | 8.2 High | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N | redhat-SADP |
Weaknesses
- CWE-20 Improper Input Validation
Affected Products
| Product | Versions |
|---|---|
koakoajs |
|
References
- https://github.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm
- https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df
- https://github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb
- https://access.redhat.com/security/cve/CVE-2026-27959vdb-entry
- RHBZ#2442928issue-tracking
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-27959.json
- https://access.redhat.com/errata/RHSA-2026:10184vendor-advisory
- https://access.redhat.com/errata/RHSA-2026:7249vendor-advisory
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