CVE-2026-27959

HIGH

7.5

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.

CVE Details

CVSS v3.1 Score7.5

SeverityHIGH

CVSS VectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Attack VectorNETWORK

ComplexityLOW

Privileges RequiredNONE

User InteractionNONE

Published2/26/2026

Last Modified2/28/2026

Sourcenvd

Honeypot Sightings0

Affected Products

koajs:koa

Weaknesses (CWE)

CWE-20

References

https://github.com/koajs/koa/commit/55ab9bab044ead4e82c70a30a4f9dc0fc9c1b6df(security-advisories@github.com)

https://github.com/koajs/koa/commit/b76ddc01fdb703e51652b0fd131d16394cadcfeb(security-advisories@github.com)

https://github.com/koajs/koa/security/advisories/GHSA-7gcc-r8m5-44qm(security-advisories@github.com)

IOC Correlations

No correlations recorded

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